Add basic support for c++17 deduction guides

core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/CModelBuilder2.java

@@ -57,6 +57,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTAliasDeclaration;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTCompositeTypeSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTCompositeTypeSpecifier.ICPPASTBaseSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclSpecifier;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTElaboratedTypeSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTExplicitTemplateInstantiation;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTFunctionDeclarator;
@@ -544,7 +545,10 @@ public class CModelBuilder2 implements IContributedModelBuilder {
 			return createTypeDef(parent, declSpecifier, declarator);
 		}
 		IASTDeclarator typeRelevant = ASTQueries.findTypeRelevantDeclarator(declarator);
-		if (typeRelevant instanceof IASTFunctionDeclarator) {
+		if (typeRelevant instanceof ICPPASTDeductionGuide) {
+			// TODO [cmodel] deduction guide
+			return null;
+		} else if (typeRelevant instanceof IASTFunctionDeclarator) {
 			return createFunctionDeclaration(parent, declSpecifier, (IASTFunctionDeclarator) typeRelevant, isTemplate);
 		}
 		return createVariable(parent, declSpecifier, declarator, isTemplate);

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/IScope.java

@@ -118,6 +118,7 @@ public interface IScope {
 		private boolean fPrefixLookup;
 		private boolean fIgnorePointOfDeclaration;
 		private boolean fArgumentDependent;
+		private boolean fDeductionGuidesOnly = false;
 
 		public ScopeLookupData(IASTName name, boolean resolve, boolean prefixLookup) {
 			if (name == null)
@@ -172,6 +173,11 @@ public interface IScope {
 			fArgumentDependent = argumentDependent;
 		}
 
+		/** @since 8.1 */
+		public final void setDeductionGuidesOnly(boolean deductionGuidesOnly) {
+			fDeductionGuidesOnly = deductionGuidesOnly;
+		}
+
 		public final void setLookupKey(char[] key) {
 			fLookupKey = key;
 		}
@@ -201,6 +207,11 @@ public interface IScope {
 			return fArgumentDependent;
 		}
 
+		/** @since 8.1 */
+		public final boolean isDeductionGuidesOnly() {
+			return fDeductionGuidesOnly;
+		}
+
 		public final IIndexFileSet getIncludedFiles() {
 			return fTu == null ? IIndexFileSet.EMPTY : fTu.getIndexFileSet();
 		}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPASTDeductionGuide.java

@@ -0,0 +1,25 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.dom.ast.cpp;
+
+/**
+ * Deduction guide, introduced in C++17.
+ *
+ * @since 8.1
+ * @noextend This interface is not intended to be extended by clients.
+ * @noimplement This interface is not intended to be implemented by clients.
+ */
+
+public interface ICPPASTDeductionGuide extends ICPPASTFunctionDeclarator {
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPClassConstructorDeductionGuide.java

@@ -0,0 +1,24 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.dom.ast.cpp;
+
+/**
+ * Marker for deduction guide synthesized from class constructor
+ *
+ * @since 8.1
+ * @noextend This interface is not intended to be extended by clients.
+ * @noimplement This interface is not intended to be implemented by clients.
+ */
+public interface ICPPClassConstructorDeductionGuide {
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPClassConstructorTemplateDeductionGuide.java

@@ -0,0 +1,24 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.dom.ast.cpp;
+
+/**
+ * Marker for deduction guide synthesized from class constructor template
+ *
+ * @since 8.1
+ * @noextend This interface is not intended to be extended by clients.
+ * @noimplement This interface is not intended to be implemented by clients.
+ */
+public interface ICPPClassConstructorTemplateDeductionGuide {
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPCopyDeductionCandidate.java

@@ -0,0 +1,24 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.dom.ast.cpp;
+
+/**
+ * Marker for copy deduction candidate used with Class Template Argument Deduction, introduced in C++17.
+ *
+ * @since 8.1
+ * @noextend This interface is not intended to be extended by clients.
+ * @noimplement This interface is not intended to be implemented by clients.
+ */
+public interface ICPPCopyDeductionCandidate {
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPDeductionGuide.java

@@ -0,0 +1,27 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.dom.ast.cpp;
+
+/**
+ * Deduction guide, introduced in C++17.
+ *
+ * @since 8.1
+ * @noextend This interface is not intended to be extended by clients.
+ * @noimplement This interface is not intended to be implemented by clients.
+ */
+public interface ICPPDeductionGuide extends ICPPBinding {
+	public static final ICPPDeductionGuide[] EMPTY_BINDING_ARRAY = {};
+
+	public ICPPFunction getFunctionBinding();
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPNodeFactory.java

@@ -253,6 +253,11 @@ public interface ICPPNodeFactory extends INodeFactory {
 	public ICPPASTFoldExpression newFoldExpression(int opToken, boolean isComma, IASTExpression lhs,
 			IASTExpression rhs);
 
+	/**
+	 * @since 8.1
+	 */
+	public ICPPASTDeductionGuide newDeductionGuide();
+
 	public ICPPASTLinkageSpecification newLinkageSpecification(String literal);
 
 	@Override

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/dom/ast/cpp/ICPPUserDefinedDeductionGuide.java

@@ -0,0 +1,24 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.dom.ast.cpp;
+
+/**
+ * Marker for user-defined deduction guide for Class Template Argument Deduction, introduced in C++17.
+ *
+ * @since 8.1
+ * @noextend This interface is not intended to be extended by clients.
+ * @noimplement This interface is not intended to be implemented by clients.
+ */
+public interface ICPPUserDefinedDeductionGuide {
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPASTDeductionGuide.java

@@ -0,0 +1,35 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.internal.core.dom.parser.cpp;
+
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeductionGuide;
+
+/**
+ * Implementation for deduction guide.
+ */
+public class CPPASTDeductionGuide extends CPPASTFunctionDeclarator implements ICPPASTDeductionGuide {
+	public CPPASTDeductionGuide() {
+	}
+
+	@Override
+	public CPPASTDeductionGuide copy() {
+		return copy(CopyStyle.withoutLocations);
+	}
+
+	@Override
+	public CPPASTDeductionGuide copy(CopyStyle style) {
+		CPPASTDeductionGuide copy = new CPPASTDeductionGuide();
+		return super.copy(copy, style);
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPASTFunctionDeclarator.java

@@ -73,13 +73,17 @@ public class CPPASTFunctionDeclarator extends CPPASTDeclarator implements ICPPAS
 	@Override
 	public CPPASTFunctionDeclarator copy(CopyStyle style) {
 		CPPASTFunctionDeclarator copy = new CPPASTFunctionDeclarator();
-		copy.varArgs = varArgs;
-		copy.pureVirtual = pureVirtual;
-		copy.isVolatile = isVolatile;
-		copy.isConst = isConst;
-		copy.isMutable = isMutable;
-		copy.refQualifier = refQualifier;
-		copy.isConstexpr = isConstexpr;
+		return copy(copy, style);
+	}
+
+	protected <T extends CPPASTFunctionDeclarator> T copy(T copy, CopyStyle style) {
+		copy.setVarArgs(varArgs);
+		copy.setPureVirtual(pureVirtual);
+		copy.setVolatile(isVolatile);
+		copy.setConst(isConst);
+		copy.setMutable(isMutable);
+		copy.setRefQualifier(refQualifier);
+		copy.setConstexpr(isConstexpr);
 
 		for (IASTParameterDeclaration param : getParameters()) {
 			copy.addParameterDeclaration(param == null ? null : param.copy(style));
@@ -97,7 +101,7 @@ public class CPPASTFunctionDeclarator extends CPPASTDeclarator implements ICPPAS
 		for (ICPPASTVirtSpecifier virtSpecifier : getVirtSpecifiers()) {
 			copy.addVirtSpecifier(virtSpecifier.copy(style));
 		}
-		return copy(copy, style);
+		return super.copy(copy, style);
 	}
 
 	@Override

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPDeductionGuide.java

@@ -0,0 +1,87 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.internal.core.dom.parser.cpp;
+
+import org.eclipse.cdt.core.dom.ILinkage;
+import org.eclipse.cdt.core.dom.ast.DOMException;
+import org.eclipse.cdt.core.dom.ast.IASTDeclarator;
+import org.eclipse.cdt.core.dom.ast.IASTName;
+import org.eclipse.cdt.core.dom.ast.IBinding;
+import org.eclipse.cdt.core.dom.ast.IScope;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPVisitor;
+import org.eclipse.core.runtime.PlatformObject;
+
+/**
+ * Represents c++17 deduction guide.
+ */
+public class CPPDeductionGuide extends PlatformObject implements ICPPDeductionGuide {
+	protected IASTDeclarator definition;
+	protected ICPPFunction functionBinding;
+
+	public CPPDeductionGuide(IASTDeclarator fnDecl, ICPPFunction functionBinding) {
+		this.definition = fnDecl;
+		this.functionBinding = functionBinding;
+	}
+
+	@Override
+	public ICPPFunction getFunctionBinding() {
+		return functionBinding;
+	}
+
+	@Override
+	public String[] getQualifiedName() throws DOMException {
+		return functionBinding.getQualifiedName();
+	}
+
+	@Override
+	public char[][] getQualifiedNameCharArray() throws DOMException {
+		return functionBinding.getQualifiedNameCharArray();
+	}
+
+	@Override
+	public boolean isGloballyQualified() throws DOMException {
+		return functionBinding.isGloballyQualified();
+	}
+
+	@Override
+	public String getName() {
+		return functionBinding.getName();
+	}
+
+	@Override
+	public char[] getNameCharArray() {
+		return functionBinding.getNameCharArray();
+	}
+
+	@Override
+	public ILinkage getLinkage() {
+		return functionBinding.getLinkage();
+	}
+
+	@Override
+	public IBinding getOwner() {
+		return functionBinding.getOwner();
+	}
+
+	protected IASTName getASTName() {
+		return definition.getName().getLastName();
+	}
+
+	@Override
+	public IScope getScope() throws DOMException {
+		return CPPVisitor.getContainingScope(getASTName());
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPNodeFactory.java

@@ -77,6 +77,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTConversionName;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclarator;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDecltypeSpecifier;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeleteExpression;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDesignatedInitializer;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTElaboratedTypeSpecifier;
@@ -577,6 +578,11 @@ public class CPPNodeFactory extends NodeFactory implements ICPPNodeFactory {
 		return new CPPASTFoldExpression(operator, fIsComma, lhs, rhs);
 	}
 
+	@Override
+	public ICPPASTDeductionGuide newDeductionGuide() {
+		return new CPPASTDeductionGuide();
+	}
+
 	@Override
 	public ICPPASTLinkageSpecification newLinkageSpecification(String literal) {
 		return new CPPASTLinkageSpecification(literal);

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPScope.java

@@ -31,6 +31,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTNamespaceDefinition;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTQualifiedName;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTTemplateId;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassScope;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPEnumScope;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPNamespace;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPNamespaceScope;
@@ -226,6 +227,12 @@ abstract public class CPPScope implements ICPPASTInternalScope {
 						CCorePlugin.log(e);
 					}
 				}
+
+				// Deduction guides are not visible to ordinary name lookup
+				if (result.length > 0) {
+					result = ArrayUtil.filter(result, lookup.isDeductionGuidesOnly() ? CPPSemantics.opIsDeductionGuide
+							: CPPSemantics.opIsNotDeductionGuide);
+				}
 			}
 		}
 
@@ -313,6 +320,11 @@ abstract public class CPPScope implements ICPPASTInternalScope {
 			binding = (IBinding) candidate;
 		}
 
+		// Deduction guides are not visible to ordinary name lookup
+		if (lookup.isDeductionGuidesOnly() ^ binding instanceof ICPPDeductionGuide) {
+			return result;
+		}
+
 		if (binding != null)
 			result = ArrayUtil.append(result, binding);
 		return result;

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/GNUCPPSourceParser.java

@@ -94,6 +94,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTConversionName;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclarator;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDecltypeSpecifier;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeleteExpression;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDesignatedInitializer;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDesignator;
@@ -2443,7 +2444,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 		}
 
 		if (LT(1) == IToken.tLPAREN) {
-			ICPPASTFunctionDeclarator dtor = functionDeclarator(true);
+			ICPPASTFunctionDeclarator dtor = functionDeclarator((IASTName) null, (IASTDeclSpecifier) null, true);
 			lambdaExpr.setDeclarator(dtor);
 			if (LT(1) == IToken.tEOC)
 				return setRange(lambdaExpr, offset, calculateEndOffset(dtor));
@@ -4292,7 +4293,10 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 	private void verifyDtor(IASTDeclSpecifier declspec, IASTDeclarator dtor, DeclarationOptions opt)
 			throws BacktrackException {
 		if (CPPVisitor.doesNotSpecifyType(declspec)) {
-			if (ASTQueries.findTypeRelevantDeclarator(dtor) instanceof IASTFunctionDeclarator) {
+			if (ASTQueries.findTypeRelevantDeclarator(dtor) instanceof IASTFunctionDeclarator typeRelevantDtor) {
+				if (typeRelevantDtor instanceof ICPPASTDeductionGuide) {
+					return;
+				}
 				boolean isQualified = false;
 				IASTName name = ASTQueries.findInnermostDeclarator(dtor).getName();
 				if (name instanceof ICPPASTQualifiedName) {
@@ -4373,7 +4377,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 	 */
 	private IASTDeclarator initDeclarator(DtorStrategy strategy, IASTDeclSpecifier declspec, DeclarationOptions option)
 			throws EndOfFileException, BacktrackException, FoundAggregateInitializer {
-		final IASTDeclarator dtor = declarator(strategy, option);
+		final IASTDeclarator dtor = declarator(strategy, declspec, option);
 		if (option.fAllowInitializer) {
 			final IASTDeclarator typeRelevantDtor = ASTQueries.findTypeRelevantDeclarator(dtor);
 			if (option != DeclarationOptions.PARAMETER && typeRelevantDtor instanceof IASTFunctionDeclarator) {
@@ -4767,7 +4771,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 	 * @throws BacktrackException
 	 *			 request a backtrack
 	 */
-	protected IASTDeclarator declarator(DtorStrategy strategy, DeclarationOptions option)
+	protected IASTDeclarator declarator(DtorStrategy strategy, IASTDeclSpecifier declspec, DeclarationOptions option)
 			throws EndOfFileException, BacktrackException {
 		final int startingOffset = LA(1).getOffset();
 		int endOffset = startingOffset;
@@ -4810,7 +4814,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 			final IASTName declaratorName = !option.fRequireSimpleName ? qualifiedName() : identifier();
 			endOffset = calculateEndOffset(declaratorName);
 			return declarator(pointerOps, hasEllipsis, declaratorName, null, startingOffset, endOffset, strategy,
-					option, attributes);
+					declspec, option, attributes);
 		}
 
 		if (lt1 == IToken.tLPAREN) {
@@ -4821,7 +4825,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 				final IToken mark = mark();
 				try {
 					cand1 = declarator(pointerOps, hasEllipsis, getNodeFactory().newName(), null, startingOffset,
-							endOffset, strategy, option, attributes);
+							endOffset, strategy, declspec, option, attributes);
 					if (option.fRequireAbstract || !option.fAllowNested || hasEllipsis)
 						return cand1;
 
@@ -4835,7 +4839,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 			if (!option.fAllowNested || hasEllipsis) {
 				if (option.fAllowAbstract) {
 					return declarator(pointerOps, hasEllipsis, getNodeFactory().newName(), null, startingOffset,
-							endOffset, strategy, option, attributes);
+							endOffset, strategy, declspec, option, attributes);
 				}
 				throwBacktrack(LA(1));
 			}
@@ -4846,10 +4850,10 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 				if (LT(1) == IToken.tRPAREN)
 					throwBacktrack(LA(1));
 
-				final IASTDeclarator nested = declarator(DtorStrategy.PREFER_FUNCTION, option);
+				final IASTDeclarator nested = declarator(DtorStrategy.PREFER_FUNCTION, declspec, option);
 				endOffset = consume(IToken.tRPAREN).getEndOffset();
 				final IASTDeclarator cand2 = declarator(pointerOps, hasEllipsis, getNodeFactory().newName(), nested,
-						startingOffset, endOffset, strategy, option, attributes);
+						startingOffset, endOffset, strategy, declspec, option, attributes);
 				if (cand1 == null || cand1End == null)
 					return cand2;
 				final IToken cand2End = LA(1);
@@ -4877,7 +4881,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 				throwBacktrack(LA(1));
 		}
 		return declarator(pointerOps, hasEllipsis, getNodeFactory().newName(), null, startingOffset, endOffset,
-				strategy, option, attributes);
+				strategy, declspec, option, attributes);
 	}
 
 	/**
@@ -5000,15 +5004,15 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 
 	private IASTDeclarator declarator(List<? extends IASTPointerOperator> pointerOps, boolean hasEllipsis,
 			IASTName declaratorName, IASTDeclarator nestedDeclarator, int startingOffset, int endOffset,
-			DtorStrategy strategy, DeclarationOptions option, List<IASTAttributeSpecifier> attributes)
-			throws EndOfFileException, BacktrackException {
+			DtorStrategy strategy, IASTDeclSpecifier declspec, DeclarationOptions option,
+			List<IASTAttributeSpecifier> attributes) throws EndOfFileException, BacktrackException {
 		ICPPASTDeclarator result = null;
 		loop: while (true) {
 			final int lt1 = LTcatchEOF(1);
 			switch (lt1) {
 			case IToken.tLPAREN:
 				if (option.fAllowFunctions && strategy == DtorStrategy.PREFER_FUNCTION) {
-					result = functionDeclarator(false);
+					result = functionDeclarator(declaratorName, declspec, false);
 					setDeclaratorID(result, hasEllipsis, declaratorName, nestedDeclarator);
 				}
 				break loop;
@@ -5086,16 +5090,47 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 		declarator.setDeclaresParameterPack(hasEllipsis);
 	}
 
+	/**
+	 * Parse a function declarator or a deduction guide, starting with the left parenthesis.
+	 */
+	private ICPPASTFunctionDeclarator functionDeclarator(IASTName declaratorName, IASTDeclSpecifier declspec,
+			boolean isLambdaDeclarator) throws EndOfFileException, BacktrackException {
+		final IToken mark = mark();
+
+		ICPPASTFunctionDeclarator fc = getNodeFactory().newFunctionDeclarator(null);
+		functionDeclarator(fc, isLambdaDeclarator);
+
+		// Test if this is a deduction guide and retry with correct object type
+		final IASTTypeId typeId = fc.getTrailingReturnType();
+		if (!isLambdaDeclarator && typeId != null && CPPVisitor.doesNotSpecifyType(declspec) && declaratorName != null
+				&& typeId.getDeclSpecifier() instanceof IASTNamedTypeSpecifier namedTypeSpec
+				&& namedTypeSpec.getName() instanceof ICPPASTTemplateId templateId) {
+
+			if (CharArrayUtils.equals(templateId.getTemplateName().getLookupKey(), declaratorName.getLookupKey())) {
+				if (declspec instanceof ICPPASTSimpleDeclSpecifier simpleDeclSpecifier) {
+					// TODO: This enables auto type resolution from return type, validate implementation in CreateType()
+					simpleDeclSpecifier.setType(IASTSimpleDeclSpecifier.t_auto);
+				}
+
+				backup(mark);
+
+				fc = getNodeFactory().newDeductionGuide();
+				functionDeclarator(fc, isLambdaDeclarator);
+			}
+		}
+
+		return fc;
+	}
+
 	/**
 	 * Parse a function declarator starting with the left parenthesis.
 	 */
-	private ICPPASTFunctionDeclarator functionDeclarator(boolean isLambdaDeclarator)
+	private void functionDeclarator(final ICPPASTFunctionDeclarator fc, boolean isLambdaDeclarator)
 			throws EndOfFileException, BacktrackException {
 		IToken last = consume(IToken.tLPAREN);
 		final int startOffset = last.getOffset();
 		int endOffset = last.getEndOffset();
 
-		final ICPPASTFunctionDeclarator fc = getNodeFactory().newFunctionDeclarator(null);
 		ICPPASTParameterDeclaration pd = null;
 		paramLoop: while (true) {
 			switch (LT(1)) {
@@ -5245,7 +5280,7 @@ public class GNUCPPSourceParser extends AbstractGNUSourceCodeParser {
 			endOffset = calculateEndOffset(typeId);
 		}
 
-		return setRange(fc, startOffset, endOffset);
+		setRange(fc, startOffset, endOffset);
 	}
 
 	/**

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPSemantics.java

@@ -157,12 +157,16 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTWhileStatement;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPAliasTemplate;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPBase;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPBlockScope;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassConstructorDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassConstructorTemplateDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassScope;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassSpecialization;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassTemplate;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassTemplatePartialSpecialization;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassType;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPConstructor;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPCopyDeductionCandidate;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeferredFunction;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPField;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
@@ -188,6 +192,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPTemplateParameter;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPTemplateScope;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPTemplateTemplateParameter;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPTemplateTypeParameter;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPUserDefinedDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPUsingDeclaration;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPUsingDirective;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPVariable;
@@ -224,10 +229,14 @@ import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPBuiltinParameter;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPCompositeBinding;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPDeferredConstructor;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPDeferredFunction;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPFunction;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPFunctionTemplate;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPFunctionType;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPImplicitConstructor;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPImplicitFunction;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPNamespace;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPNamespaceScope;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPParameter;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPPointerType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPReferenceType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPScope;
@@ -274,6 +283,13 @@ public class CPPSemantics {
 	private static final char[] CALL_FUNCTION = "call-function".toCharArray(); //$NON-NLS-1$
 	private static final ICPPEvaluation[] NO_INITCLAUSE_EVALUATION = {};
 
+	public static final IUnaryPredicate<IBinding> opIsDeductionGuide = (argument) -> {
+		return argument instanceof ICPPDeductionGuide;
+	};
+	public static final IUnaryPredicate<IBinding> opIsNotDeductionGuide = (argument) -> {
+		return !(argument instanceof ICPPDeductionGuide);
+	};
+
 	// Set to true for debugging.
 	public static boolean traceBindingResolution = false;
 	public static int traceIndent = 0;
@@ -399,6 +415,289 @@ public class CPPSemantics {
 		return postResolution(binding, data);
 	}
 
+	private static IBinding doClassTemplateArgumentDeduction(ICPPClassTemplate classTemplate, LookupData data) {
+		// Implementation common to all candidate function non-templates
+		class CTADDeductionCandidateProbeFunction extends CPPFunction {
+			ICPPFunction method;
+			ICPPFunctionType functionType;
+
+			public CTADDeductionCandidateProbeFunction(ICPPFunction method) {
+				super(null);
+				this.method = method;
+			}
+
+			@Override
+			public char[] getNameCharArray() {
+				return method.getNameCharArray();
+			}
+
+			@Override
+			public ICPPFunctionType getType() {
+				if (functionType == null) {
+					ICPPFunctionType ft = method.getType();
+					functionType = new CPPFunctionType(ft.getReturnType(), ft.getParameterTypes(),
+							ft.getNoexceptSpecifier(), ft.isConst(), ft.isVolatile(), ft.hasRefQualifier(),
+							ft.isRValueReference(), ft.takesVarArgs());
+				}
+
+				return functionType;
+			}
+
+			@Override
+			public IType[] getExceptionSpecification() {
+				return method.getExceptionSpecification();
+			}
+
+			@Override
+			public ICPPParameter[] getParameters() {
+				return method.getParameters();
+			}
+
+			@Override
+			public boolean takesVarArgs() {
+				return method.takesVarArgs();
+			}
+
+			@Override
+			public boolean hasParameterPack() {
+				return method.hasParameterPack();
+			}
+		}
+
+		// Implementation common to all candidate function templates
+		class CTADDeductionCandidateProbeFunctionTemplate extends CPPFunctionTemplate {
+			ICPPClassTemplate classTemplate;
+			ICPPFunction method;
+			boolean isClassConstructor;
+			private ICPPTemplateParameter[] deductionTemplateParameters;
+			ICPPFunctionType functionType;
+
+			private final void resetCachedValues() {
+				deductionTemplateParameters = null;
+				functionType = null;
+			}
+
+			public CTADDeductionCandidateProbeFunctionTemplate(ICPPClassTemplate classTemplate) {
+				super(null);
+				this.classTemplate = classTemplate;
+			}
+
+			public CTADDeductionCandidateProbeFunctionTemplate(ICPPClassTemplate classTemplate, ICPPFunction method,
+					boolean isClassConstructor) {
+				this(classTemplate);
+				setMethod(method);
+				setIsClassConstructor(isClassConstructor);
+			}
+
+			protected void setMethod(ICPPFunction method) {
+				this.method = method;
+				resetCachedValues(); // Force recalculation of type and template args
+			}
+
+			protected void setIsClassConstructor(boolean isClassConstructor) {
+				this.isClassConstructor = isClassConstructor;
+				resetCachedValues(); // Force recalculation of type and template args
+			}
+
+			@Override
+			public char[] getNameCharArray() {
+				return method.getNameCharArray();
+			}
+
+			@Override
+			public ICPPFunctionType getType() {
+				if (functionType == null) {
+					ICPPFunctionType ft = method.getType();
+					IType returnType;
+					if (isClassConstructor) {
+						returnType = (ICPPClassType) classTemplate.asDeferredInstance();
+					} else {
+						returnType = ft.getReturnType();
+					}
+					functionType = new CPPFunctionType(returnType, ft.getParameterTypes(), ft.getNoexceptSpecifier(),
+							ft.isConst(), ft.isVolatile(), ft.hasRefQualifier(), ft.isRValueReference(),
+							ft.takesVarArgs());
+				}
+
+				return functionType;
+			}
+
+			@Override
+			public IType[] getExceptionSpecification() {
+				//return method.getExceptionSpecification();
+				// TODO: this requires class owner; see if exception specification is required to implement CTAD
+				return IType.EMPTY_TYPE_ARRAY;
+			}
+
+			@Override
+			public ICPPParameter[] getParameters() {
+				return method.getParameters();
+			}
+
+			@Override
+			public boolean takesVarArgs() {
+				return method.takesVarArgs();
+			}
+
+			@Override
+			public boolean hasParameterPack() {
+				return method.hasParameterPack();
+			}
+
+			@Override
+			public ICPPTemplateParameter[] getTemplateParameters() {
+				// TODO: make sure template parameter identifiers are consistent with where parameters are coming from
+				// Maybe need to re-instantiate all of them?
+				if (deductionTemplateParameters == null) {
+					ICPPTemplateParameter[] candParams = ICPPTemplateParameter.EMPTY_TEMPLATE_PARAMETER_ARRAY;
+					if (isClassConstructor) {
+						candParams = ArrayUtil.addAll(candParams, classTemplate.getTemplateParameters());
+					}
+					if (method instanceof ICPPTemplateDefinition ctorTemplate) {
+						candParams = ArrayUtil.addAll(candParams, ctorTemplate.getTemplateParameters());
+					}
+					deductionTemplateParameters = ArrayUtil.trim(candParams);
+				}
+				return deductionTemplateParameters;
+			}
+		}
+
+		// Implementation for candidate function synthesized from constructor non-template
+		class CTADGuideFromConstructor extends CTADDeductionCandidateProbeFunctionTemplate
+				implements ICPPClassConstructorDeductionGuide {
+
+			public CTADGuideFromConstructor(ICPPClassTemplate classTemplate, ICPPFunction method) {
+				super(classTemplate, method, true);
+			}
+		}
+
+		// Implementation for candidate function synthesized from constructor template
+		class CTADGuideFromConstructorTemplate extends CTADDeductionCandidateProbeFunctionTemplate
+				implements ICPPClassConstructorTemplateDeductionGuide {
+
+			public CTADGuideFromConstructorTemplate(ICPPClassTemplate classTemplate, ICPPFunction method) {
+				super(classTemplate, method, true);
+			}
+		}
+
+		// Implementation for candidate function from user-defined template deduction guide
+		class CTADUserDefinedGuideTemplate extends CTADDeductionCandidateProbeFunctionTemplate
+				implements ICPPUserDefinedDeductionGuide {
+
+			public CTADUserDefinedGuideTemplate(ICPPClassTemplate classTemplate, ICPPTemplateDefinition method) {
+				super(classTemplate, (ICPPFunction) method, false);
+			}
+		}
+
+		// Implementation for candidate function from user-defined non-template deduction guide
+		class CTADUserDefinedGuide extends CTADDeductionCandidateProbeFunction
+				implements ICPPUserDefinedDeductionGuide {
+
+			public CTADUserDefinedGuide(ICPPFunction method) {
+				super(method);
+			}
+		}
+
+		// Implementation for "copy deduction candidate" synthesized from hypothetical constructor C(C)
+		class CTADCopyDeductionCandidate extends CTADDeductionCandidateProbeFunctionTemplate
+				implements ICPPCopyDeductionCandidate {
+
+			public CTADCopyDeductionCandidate(ICPPClassTemplate classTemplate) {
+				super(classTemplate);
+
+				char[] className = classTemplate.getNameCharArray();
+
+				ICPPParameter[] copyDeductionCandidateParams = new ICPPParameter[] {
+						new CPPParameter((ICPPClassType) classTemplate.asDeferredInstance(), 0) };
+				ICPPMethod copyDeductionCandidate = new CPPImplicitConstructor(
+						(ICPPClassScope) classTemplate.getCompositeScope(), className, copyDeductionCandidateParams,
+						null);
+
+				setMethod(copyDeductionCandidate);
+				setIsClassConstructor(true);
+			}
+		}
+
+		final IASTName lookupName = data.getLookupName();
+		if (lookupName == null)
+			return classTemplate;
+
+		char[] className = lookupName.getLookupKey();
+
+		ICPPConstructor[] ctors = classTemplate.getConstructors();
+
+		ICPPFunction[] deductionGuideCandidateFunctions = new ICPPFunction[ctors.length + 1];
+
+		if (ctors.length > 0) {
+			// Add template probe functions synthesized from class constructors
+			for (ICPPConstructor ctor : ctors) {
+				if (ctor instanceof ICPPTemplateDefinition ctorTemplate) {
+					deductionGuideCandidateFunctions = ArrayUtil.append(deductionGuideCandidateFunctions,
+							new CTADGuideFromConstructorTemplate(classTemplate, ctor));
+				} else {
+					deductionGuideCandidateFunctions = ArrayUtil.append(deductionGuideCandidateFunctions,
+							new CTADGuideFromConstructor(classTemplate, ctor));
+				}
+			}
+		} else {
+			// If class is not defined or does not declare any constructors, add hypothetical constructor C()
+			ICPPMethod defaultConstructor = new CPPImplicitConstructor(
+					(ICPPClassScope) classTemplate.getCompositeScope(), className,
+					ICPPParameter.EMPTY_CPPPARAMETER_ARRAY, null);
+
+			deductionGuideCandidateFunctions = ArrayUtil.append(deductionGuideCandidateFunctions,
+					new CTADDeductionCandidateProbeFunctionTemplate(classTemplate, defaultConstructor, true));
+		}
+
+		deductionGuideCandidateFunctions = ArrayUtil.append(deductionGuideCandidateFunctions,
+				new CTADCopyDeductionCandidate(classTemplate));
+
+		// Add user-defined deduction guides
+		try {
+			// TODO: add support for lookup in containing class scope of classTemplate
+			IScope lookupScope = getContainingNamespaceScope(classTemplate, data.getTranslationUnit());
+
+			if (lookupScope instanceof ICPPASTInternalScope internalScope) {
+
+				LookupData guideLookupData = new LookupData(className, null, lookupName);
+				guideLookupData.setDeductionGuidesOnly(true);
+
+				IBinding[] bindings = getBindingsFromScope(internalScope, guideLookupData);
+
+				for (IBinding binding : bindings) {
+					if (binding instanceof ICPPDeductionGuide guide) {
+						IBinding guideBinding = guide.getFunctionBinding();
+
+						if (guideBinding instanceof ICPPTemplateDefinition guideFunctionTemplate) {
+							deductionGuideCandidateFunctions = ArrayUtil.append(deductionGuideCandidateFunctions,
+									new CTADUserDefinedGuideTemplate(classTemplate, guideFunctionTemplate));
+						} else if (guideBinding instanceof ICPPFunction guideFunction) {
+							deductionGuideCandidateFunctions = ArrayUtil.append(deductionGuideCandidateFunctions,
+									new CTADUserDefinedGuide(guideFunction));
+						}
+					}
+				}
+			}
+		} catch (DOMException e) {
+		}
+
+		// Perform overload resolution for initializer clause.
+		// Deduced class type is the return type of the function selected by overload resolution.
+		try {
+			IBinding resolved = resolveFunction(data, deductionGuideCandidateFunctions, true, false);
+
+			if (resolved instanceof ICPPFunction selected) {
+				if (selected.getType().getReturnType() instanceof IBinding binding) {
+					return binding;
+				}
+			}
+		} catch (DOMException e) {
+		}
+
+		// Not deduced
+		return null;
+	}
+
 	private static IBinding postResolution(IBinding binding, LookupData data) {
 		final IASTName lookupName = data.getLookupName();
 		if (lookupName == null)
@@ -468,17 +767,61 @@ public class CPPSemantics {
 		 */
 		if (binding instanceof ICPPClassTemplate && !(binding instanceof ICPPClassSpecialization)
 				&& !(binding instanceof ICPPTemplateParameter) && !(lookupName instanceof ICPPASTTemplateId)) {
+
 			ASTNodeProperty prop = lookupName.getPropertyInParent();
-			if (prop != ICPPASTTemplateId.TEMPLATE_NAME && !lookupName.isQualified()) {
+			if (prop != ICPPASTTemplateId.TEMPLATE_NAME) {
+				if (!lookupName.isQualified()) {
 					// You cannot use a class template name outside of the class template scope,
-				// mark it as a problem.
+					// mark it as a problem - unless Class Template Argument Deduction needs to be done
 					IBinding user = CPPTemplates.isUsedInClassTemplateScope((ICPPClassTemplate) binding, lookupName);
 					if (user instanceof ICPPClassTemplate) {
 						binding = ((ICPPClassTemplate) user).asDeferredInstance();
 					} else if (user != null) {
 						binding = user;
 					} else {
+						// Attempt class template argument deduction if appropriate
+						if (data.getTranslationUnit().getEnableClassTemplateArgumentDeduction()) {
+							if (lookupName.getParent() instanceof IASTIdExpression idExpression
+									&& idExpression.getPropertyInParent() == IASTFunctionCallExpression.FUNCTION_NAME) {
+
+								// Class name for class type argument deduction is a type
+								return doClassTemplateArgumentDeduction((ICPPClassTemplate) binding, data);
+							}
+						}
 						boolean ok = false;
+						// Attempt class template argument deduction if appropriate
+						if (data.getTranslationUnit().getEnableClassTemplateArgumentDeduction()
+								&& lookupName.getParent() instanceof IASTNamedTypeSpecifier namedTypeSpecifier
+								&& namedTypeSpecifier.getPropertyInParent() == IASTSimpleDeclaration.DECL_SPECIFIER
+								&& namedTypeSpecifier.getParent() instanceof IASTSimpleDeclaration declaration) {
+
+							IASTDeclarator[] declarators = declaration.getDeclarators();
+							if (declarators != null && declarators.length > 0) {
+								IASTDeclarator declarator = declarators[0];
+
+								// Cannot deduce pointer or reference class template argument
+								if (declarator.getPointerOperators().length == 0) {
+									// Class name for class type argument deduction is a type
+									ICPPASTInitializerClause initializerClause = CPPVisitor
+											.getAutoInitClauseForDeclarator(declarator);
+									if (initializerClause != null) {
+										data.setFunctionArguments(false,
+												new ICPPASTInitializerClause[] { initializerClause });
+									} else {
+										data.setFunctionArguments(false, NO_INITCLAUSE_EVALUATION);
+									}
+									IBinding b = doClassTemplateArgumentDeduction((ICPPClassTemplate) binding, data);
+
+									if (b != null) {
+										// Deduced class template arguments
+										binding = b;
+										// No need to check other cases
+										ok = true;
+									}
+								}
+							}
+						}
+
 						IASTNode node = lookupName.getParent();
 						while (node != null && !ok) {
 							if (node instanceof ICPPASTTemplateId
@@ -504,6 +847,41 @@ public class CPPSemantics {
 									data.getFoundBindings());
 						}
 					}
+
+				} else {
+					// Name is qualified-name
+					// Attempt class template argument deduction if appropriate
+					if (data.getTranslationUnit().getEnableClassTemplateArgumentDeduction()
+							&& lookupName.getParent() instanceof ICPPASTQualifiedName qualifiedName
+							&& qualifiedName.getParent() instanceof IASTNamedTypeSpecifier namedTypeSpecifier
+							&& namedTypeSpecifier.getPropertyInParent() == IASTSimpleDeclaration.DECL_SPECIFIER
+							&& namedTypeSpecifier.getParent() instanceof IASTSimpleDeclaration declaration) {
+
+						IASTDeclarator[] declarators = declaration.getDeclarators();
+						if (declarators != null && declarators.length > 0) {
+							IASTDeclarator declarator = declarators[0];
+
+							// Cannot deduce pointer or reference class template argument
+							if (declarator.getPointerOperators().length == 0) {
+								// Class name for class type argument deduction is a type
+								ICPPASTInitializerClause initializerClause = CPPVisitor
+										.getAutoInitClauseForDeclarator(declarator);
+								if (initializerClause != null) {
+									data.setFunctionArguments(false,
+											new ICPPASTInitializerClause[] { initializerClause });
+								} else {
+									data.setFunctionArguments(false, NO_INITCLAUSE_EVALUATION);
+								}
+								IBinding b = doClassTemplateArgumentDeduction((ICPPClassTemplate) binding, data);
+
+								if (b != null) {
+									// Deduced class template arguments
+									binding = b;
+								}
+							}
+						}
+					}
+				}
 			}
 		} else if (binding instanceof ICPPDeferredClassInstance) {
 			// Try to replace binding by the one pointing to the enclosing template declaration.
@@ -1442,6 +1820,12 @@ public class CPPSemantics {
 			});
 		}
 
+		// Deduction guides are not visible to ordinary name lookup
+		if (bindings.length > 0) {
+			bindings = ArrayUtil.filter(bindings,
+					data.isDeductionGuidesOnly() ? opIsDeductionGuide : opIsNotDeductionGuide);
+		}
+
 		return expandUsingDeclarationsAndRemoveObjects(bindings, data);
 	}
 
@@ -1863,8 +2247,9 @@ public class CPPSemantics {
 						declarator = declarator.getNestedDeclarator();
 					}
 					if (innermost != null) {
-						IASTName declaratorName = innermost.getName();
-						ASTInternal.addName(scope, declaratorName);
+						// NOTE This now may include deduction guides which are filtered later during lookup
+						IASTName declaratorOrDeductionGuideName = innermost.getName();
+						ASTInternal.addName(scope, declaratorOrDeductionGuideName);
 					}
 				}
 			}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java

@@ -117,6 +117,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTConstructorInitializer;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTConversionName;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeclarator;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTElaboratedTypeSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTEnumerationSpecifier;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTExplicitTemplateInstantiation;
@@ -212,6 +213,7 @@ import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPClassType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPClosureType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPConstructor;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPConstructorTemplate;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPDeductionGuide;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPEnumeration;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPEnumerator;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPField;
@@ -883,6 +885,7 @@ public class CPPVisitor extends ASTQueries {
 			binding = scope.getBinding(name, forceResolve);
 		}
 
+		boolean isDeductionGuide = false;
 		boolean isFunction = false;
 		if (parent instanceof ICPPASTFunctionDefinition) {
 			isFunction = true;
@@ -908,6 +911,9 @@ public class CPPVisitor extends ASTQueries {
 				binding = td;
 			} else if (typeRelevantDtor instanceof IASTFunctionDeclarator) {
 				// Function declaration via function declarator.
+				if (typeRelevantDtor instanceof ICPPASTDeductionGuide) {
+					isDeductionGuide = true;
+				}
 				isFunction = true;
 			} else {
 				// Looks like a variable declaration.
@@ -991,11 +997,17 @@ public class CPPVisitor extends ASTQueries {
 			} else {
 				binding = template ? (ICPPFunction) new CPPFunctionTemplate(name) : new CPPFunction(typeRelevantDtor);
 			}
+
+			if (isDeductionGuide) {
+				binding = new CPPDeductionGuide(typeRelevantDtor, (ICPPFunction) binding);
+			} else {
 				binding = CPPSemantics.checkDeclSpecifier(binding, name, parent);
+
 				if (isFriendDecl && scope instanceof IASTInternalScope) {
 					((IASTInternalScope) scope).addBinding(binding);
 				}
 			}
+		}
 
 		return binding;
 	}
@@ -2473,7 +2485,7 @@ public class CPPVisitor extends ASTQueries {
 		return autoInitClause;
 	}
 
-	private static ICPPASTInitializerClause getAutoInitClauseForDeclarator(IASTDeclarator declarator) {
+	protected static ICPPASTInitializerClause getAutoInitClauseForDeclarator(IASTDeclarator declarator) {
 		IASTInitializer initClause = declarator.getInitializer();
 		return getInitClauseForInitializer(initClause);
 	}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/FunctionCost.java

@@ -28,12 +28,16 @@ import org.eclipse.cdt.core.dom.ast.IASTTranslationUnit;
 import org.eclipse.cdt.core.dom.ast.IBinding;
 import org.eclipse.cdt.core.dom.ast.IFunction;
 import org.eclipse.cdt.core.dom.ast.IType;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassConstructorDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassConstructorTemplateDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassType;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPCopyDeductionCandidate;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunctionTemplate;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunctionType;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPMethod;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPSpecialization;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPUserDefinedDeductionGuide;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.OverloadableOperator;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPTemplates.TypeSelection;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.Cost.DeferredUDC;
@@ -195,6 +199,10 @@ class FunctionCost {
 			if (cmp != 0)
 				return cmp;
 
+			cmp = compareAsDeductionGuides(f1, f2);
+			if (cmp != 0)
+				return cmp;
+
 			// At this point prefer non-index bindings
 			return -CPPSemantics.compareByRelevance(tu, f1, f2);
 		}
@@ -205,6 +213,43 @@ class FunctionCost {
 		return 1;
 	}
 
+	private int compareAsDeductionGuides(ICPPFunction f1, ICPPFunction f2) {
+		ICPPFunction deductionCandidate = asTemplate(f1);
+		if (deductionCandidate == null) {
+			deductionCandidate = f1;
+		}
+		ICPPFunction otherDeductionCandidate = asTemplate(f2);
+		if (otherDeductionCandidate == null) {
+			otherDeductionCandidate = f2;
+		}
+
+		// 16.3.3-1.12 F1 is generated from a deduction-guide and F2 is not
+		final boolean isUserDefinedDeductionGuide = deductionCandidate instanceof ICPPUserDefinedDeductionGuide;
+		final boolean otherUserDefinedDeductionGuide = otherDeductionCandidate instanceof ICPPUserDefinedDeductionGuide;
+
+		if (isUserDefinedDeductionGuide != otherUserDefinedDeductionGuide) {
+			return isUserDefinedDeductionGuide ? -1 : 1;
+		}
+
+		// 16.3.3-1.13 F1 is the copy deduction candidate and F2 is not
+		final boolean isCopyDeductionCandidate = deductionCandidate instanceof ICPPCopyDeductionCandidate;
+		final boolean otherCopyDeductionCandidate = otherDeductionCandidate instanceof ICPPCopyDeductionCandidate;
+
+		if (isCopyDeductionCandidate != otherCopyDeductionCandidate) {
+			return isCopyDeductionCandidate ? -1 : 1;
+		}
+
+		// 16.3.3-1.14 F1 is generated from a non-template constructor and F2 is generated from a constructor template
+		final boolean isFromNonTemplateConstructor = deductionCandidate instanceof ICPPClassConstructorDeductionGuide;
+		final boolean otherFromTemplateConstructor = otherDeductionCandidate instanceof ICPPClassConstructorTemplateDeductionGuide;
+
+		if (isFromNonTemplateConstructor && otherFromTemplateConstructor) {
+			return -1;
+		}
+
+		return 0;
+	}
+
 	private int overridesUsingDeclaration(ICPPFunction f1, ICPPFunction f2) {
 		if (f1.takesVarArgs() != f2.takesVarArgs())
 			return 0;

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/IIndexCPPBindingConstants.java

@@ -77,4 +77,6 @@ public interface IIndexCPPBindingConstants {
 	int CPP_FIELD_TEMPLATE_PARTIAL_SPECIALIZATION = IIndexBindingConstants.LAST_CONSTANT + 60;
 	int CPP_DEFERRED_VARIABLE_INSTANCE = IIndexBindingConstants.LAST_CONSTANT + 61;
 	int CPP_ALIAS_TEMPLATE_SPECIALIZATION = IIndexBindingConstants.LAST_CONSTANT + 62;
+	int CPP_DEDUCTION_GUIDE = IIndexBindingConstants.LAST_CONSTANT + 63;
+	int CPP_DEDUCTION_GUIDE_TEMPLATE = IIndexBindingConstants.LAST_CONSTANT + 64;
 }

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/composite/cpp/CPPCompositesFactory.java

@@ -36,6 +36,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassTemplatePartialSpecialization;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassTemplatePartialSpecializationSpecialization;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassType;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPConstructor;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPEnumScope;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPEnumeration;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPField;
@@ -753,6 +754,8 @@ public class CPPCompositesFactory extends AbstractCompositeFactory {
 					return new CompositeCPPConstructorTemplate(this, (ICPPConstructor) binding);
 				} else if (binding instanceof ICPPMethod) {
 					return new CompositeCPPMethodTemplate(this, (ICPPMethod) binding);
+				} else if (binding instanceof ICPPDeductionGuide guide) {
+					return new CompositeCPPDeductionGuideTemplate(this, guide);
 				} else if (binding instanceof ICPPFunctionTemplate) {
 					return new CompositeCPPFunctionTemplate(this, (ICPPFunction) binding);
 				} else if (binding instanceof ICPPAliasTemplate) {
@@ -810,6 +813,8 @@ public class CPPCompositesFactory extends AbstractCompositeFactory {
 			} else if (binding instanceof ICPPEnumeration) {
 				ICPPEnumeration def = (ICPPEnumeration) findOneBinding(binding);
 				result = def == null ? null : new CompositeCPPEnumeration(this, def);
+			} else if (binding instanceof ICPPDeductionGuide guide) {
+				result = new CompositeCPPDeductionGuide(this, guide);
 			} else if (binding instanceof ICPPFunction) {
 				result = new CompositeCPPFunction(this, (ICPPFunction) binding);
 			} else if (binding instanceof ICPPInternalEnumerator) {

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/composite/cpp/CompositeCPPDeductionGuide.java

@@ -0,0 +1,29 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.internal.core.index.composite.cpp;
+
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
+import org.eclipse.cdt.internal.core.index.composite.ICompositesFactory;
+
+public class CompositeCPPDeductionGuide extends CompositeCPPFunction implements ICPPDeductionGuide {
+	public CompositeCPPDeductionGuide(ICompositesFactory cf, ICPPDeductionGuide rbinding) {
+		super(cf, rbinding.getFunctionBinding());
+	}
+
+	@Override
+	public ICPPFunction getFunctionBinding() {
+		return this;
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/composite/cpp/CompositeCPPDeductionGuideTemplate.java

@@ -0,0 +1,29 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.internal.core.index.composite.cpp;
+
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
+import org.eclipse.cdt.internal.core.index.composite.ICompositesFactory;
+
+public class CompositeCPPDeductionGuideTemplate extends CompositeCPPFunctionTemplate implements ICPPDeductionGuide {
+	public CompositeCPPDeductionGuideTemplate(ICompositesFactory cf, ICPPDeductionGuide rbinding) {
+		super(cf, rbinding.getFunctionBinding());
+	}
+
+	@Override
+	public ICPPFunction getFunctionBinding() {
+		return this;
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPDeductionGuide.java

@@ -0,0 +1,43 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.internal.core.pdom.dom.cpp;
+
+import org.eclipse.cdt.core.dom.ast.DOMException;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
+import org.eclipse.cdt.internal.core.index.IIndexCPPBindingConstants;
+import org.eclipse.cdt.internal.core.pdom.dom.PDOMLinkage;
+import org.eclipse.cdt.internal.core.pdom.dom.PDOMNode;
+import org.eclipse.core.runtime.CoreException;
+
+public class PDOMCPPDeductionGuide extends PDOMCPPFunction implements ICPPDeductionGuide {
+	public PDOMCPPDeductionGuide(PDOMLinkage linkage, long bindingRecord) {
+		super(linkage, bindingRecord);
+	}
+
+	public PDOMCPPDeductionGuide(PDOMCPPLinkage linkage, PDOMNode parent, ICPPDeductionGuide guide)
+			throws CoreException, DOMException {
+		super(linkage, parent, guide.getFunctionBinding(), true);
+	}
+
+	@Override
+	public int getNodeType() {
+		return IIndexCPPBindingConstants.CPP_DEDUCTION_GUIDE;
+	}
+
+	@Override
+	public ICPPFunction getFunctionBinding() {
+		return this;
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPDeductionGuideTemplate.java

@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Igor V. Kovalenko.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Igor V. Kovalenko - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.internal.core.pdom.dom.cpp;
+
+import org.eclipse.cdt.core.dom.ast.DOMException;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunctionTemplate;
+import org.eclipse.cdt.internal.core.index.IIndexCPPBindingConstants;
+import org.eclipse.cdt.internal.core.pdom.dom.PDOMLinkage;
+import org.eclipse.cdt.internal.core.pdom.dom.PDOMNode;
+import org.eclipse.core.runtime.CoreException;
+
+public class PDOMCPPDeductionGuideTemplate extends PDOMCPPFunctionTemplate implements ICPPDeductionGuide {
+	public PDOMCPPDeductionGuideTemplate(PDOMLinkage linkage, long bindingRecord) {
+		super(linkage, bindingRecord);
+	}
+
+	public PDOMCPPDeductionGuideTemplate(PDOMCPPLinkage linkage, PDOMNode parent, ICPPDeductionGuide guide)
+			throws CoreException, DOMException {
+		super(linkage, parent, (ICPPFunctionTemplate) guide.getFunctionBinding());
+	}
+
+	@Override
+	public int getNodeType() {
+		return IIndexCPPBindingConstants.CPP_DEDUCTION_GUIDE_TEMPLATE;
+	}
+
+	@Override
+	public ICPPFunction getFunctionBinding() {
+		return this;
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPLinkage.java

@@ -60,6 +60,7 @@ import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassTemplate;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassTemplatePartialSpecialization;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPClassType;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPConstructor;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPDeductionGuide;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPEnumeration;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPField;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPFieldTemplate;
@@ -851,6 +852,12 @@ class PDOMCPPLinkage extends PDOMLinkage implements IIndexCPPBindingConstants {
 			if (parent instanceof PDOMCPPClassType || parent instanceof PDOMCPPClassSpecialization) {
 				pdomBinding = new PDOMCPPMethod(this, parent, (ICPPMethod) binding);
 			}
+		} else if (binding instanceof ICPPDeductionGuide guide) {
+			if (guide.getFunctionBinding() instanceof ICPPFunctionTemplate) {
+				pdomBinding = new PDOMCPPDeductionGuideTemplate(this, parent, guide);
+			} else {
+				pdomBinding = new PDOMCPPDeductionGuide(this, parent, guide);
+			}
 		} else if (binding instanceof ICPPFunction) {
 			pdomBinding = new PDOMCPPFunction(this, parent, (ICPPFunction) binding, true);
 		} else if (binding instanceof ICPPNamespaceAlias) {
@@ -1137,6 +1144,12 @@ class PDOMCPPLinkage extends PDOMLinkage implements IIndexCPPBindingConstants {
 		} else if (binding instanceof ICPPMethod) {
 			// this must be before functions
 			return CPPMETHOD;
+		} else if (binding instanceof ICPPDeductionGuide guide) {
+			if (guide.getFunctionBinding() instanceof ICPPFunctionTemplate) {
+				return CPP_DEDUCTION_GUIDE_TEMPLATE;
+			} else {
+				return CPP_DEDUCTION_GUIDE;
+			}
 		} else if (binding instanceof ICPPFunction) {
 			return CPPFUNCTION;
 		} else if (binding instanceof ICPPUnknownBinding) {
@@ -1403,6 +1416,10 @@ class PDOMCPPLinkage extends PDOMLinkage implements IIndexCPPBindingConstants {
 			return new PDOMCPPFieldTemplatePartialSpecialization(this, record);
 		case CPP_ALIAS_TEMPLATE_SPECIALIZATION:
 			return new PDOMCPPAliasTemplateSpecialization(this, record);
+		case CPP_DEDUCTION_GUIDE:
+			return new PDOMCPPDeductionGuide(this, record);
+		case CPP_DEDUCTION_GUIDE_TEMPLATE:
+			return new PDOMCPPDeductionGuideTemplate(this, record);
 		}
 		assert false : "nodeid= " + nodeType; //$NON-NLS-1$
 		return null;