Bug 562452: Avoid using .C for C++ files when calculating specs

Change-Id: I0fe24a8343e73d501ae09e8bf3721e3d310a696d

build/org.eclipse.cdt.managedbuilder.core/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: %pluginName
 Bundle-SymbolicName: org.eclipse.cdt.managedbuilder.core; singleton:=true
-Bundle-Version: 8.8.0.qualifier
+Bundle-Version: 8.9.0.qualifier
 Bundle-Activator: org.eclipse.cdt.managedbuilder.core.ManagedBuilderCorePlugin
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin

build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/language/settings/providers/AbstractBuiltinSpecsDetector.java

@@ -26,6 +26,7 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Optional;
 import java.util.Set;
 
 import org.eclipse.cdt.core.CCorePlugin;
@@ -894,23 +895,41 @@ public abstract class AbstractBuiltinSpecsDetector extends AbstractLanguageSetti
 	 * @return file extension associated with the language or {@code null} if not found.
 	 */
 	protected String getSpecFileExtension(String languageId) {
-		String ext = null;
+		Optional<String> extension = Optional.empty();
 		ILanguageDescriptor langDescriptor = LanguageManager.getInstance().getLanguageDescriptor(languageId);
 		if (langDescriptor != null) {
 			IContentType[] contentTypes = langDescriptor.getContentTypes();
 			if (contentTypes != null && contentTypes.length > 0) {
 				String[] fileExtensions = contentTypes[0].getFileSpecs(IContentType.FILE_EXTENSION_SPEC);
-				if (fileExtensions != null && fileExtensions.length > 0) {
+				if (fileExtensions != null) {
-					ext = fileExtensions[0];
+					List<String> extensions = Arrays.asList(fileExtensions);
+					extension = selectBestSpecFileExtension(extensions);
 				}
 			}
 		}
 
-		if (ext == null) {
+		if (!extension.isPresent()) {
 			ManagedBuilderCorePlugin.log(new Status(IStatus.ERROR, ManagedBuilderCorePlugin.PLUGIN_ID,
 					"Unable to find file extension for language " + languageId)); //$NON-NLS-1$
+			return null;
 		}
-		return ext;
+		return extension.get();
+	}
+
+	/**
+	 * Return the best extension to use for calculating spec file from a list of extensions.
+	 * @param extensions list of possible extensions to choose from
+	 * @return one of the extensions deemed the best one to use from the list
+	 * @since 8.9
+	 */
+	protected Optional<String> selectBestSpecFileExtension(List<String> extensions) {
+		return extensions.stream().filter(s -> s != null && !s.isEmpty()).findFirst().map(ext -> {
+			// Bug 562452: Special case where we prefer not to use .C for c++ files.
+			if ("C".equals(ext) && extensions.contains("cpp")) { //$NON-NLS-1$//$NON-NLS-2$
+				return "cpp"; //$NON-NLS-1$
+			}
+			return ext;
+		});
 	}
 
 	/**

build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/language/settings/providers/ToolchainBuiltinSpecsDetector.java

@@ -16,6 +16,7 @@
 package org.eclipse.cdt.managedbuilder.language.settings.providers;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -139,19 +140,17 @@ public abstract class ToolchainBuiltinSpecsDetector extends AbstractBuiltinSpecs
 
 	@Override
 	protected String getSpecFileExtension(String languageId) {
-		Optional<String> found = languageTool(languageId)//
+		Optional<String[]> optionalExtensions = languageTool(languageId)
-				.flatMap(t -> Optional.of(t.getAllInputExtensions()))//
+				.flatMap(t -> Optional.of(t.getAllInputExtensions()));
-				.flatMap(e -> Arrays.asList(e).stream().findFirst());
+		List<String> extensions = optionalExtensions.map(Arrays::asList).orElseGet(() -> Collections.emptyList());
-		if (!found.isPresent()) {
+		Optional<String> extension = selectBestSpecFileExtension(extensions);
+
+		if (!extension.isPresent()) {
+			//this looks like either invalid configuration settings or API issue
 			ManagedBuilderCorePlugin.error(NLS.bind("Unable to find file extension for language {0}", languageId)); //$NON-NLS-1$
 			return null;
 		}
-		String firstInput = found.get();
+		return extension.get();
-		if (firstInput == null || firstInput.isEmpty()) {
-			//this looks like either invalid configuration settings or API issue
-			ManagedBuilderCorePlugin.error(NLS.bind("Unable to find file extension for language {0}", languageId)); //$NON-NLS-1$
-		}
-		return firstInput;
 	}
 
 	@Override