Use optionally computed content type from CompareConfiguration

Detected content type id could be retrieved now from the
CompareConfiguration with the CONTENT_TYPE key (see
eclipse-platform/eclipse.platform#1294).

Use this value (if available) as fallbackContentTypes in
ExtensionBasedTextViewerConfiguration.

The allows GenericEditorMergeViewer to know for which content type
was it actually created and so use that in cases where the content type
can't be derived from the input (like data from git revisions
that don't have regular files or buffers associated to the viewer).

Fixes eclipse-platform#1747

bundles/org.eclipse.ui.genericeditor/META-INF/MANIFEST.MF

@@ -15,7 +15,7 @@ Require-Bundle: org.eclipse.ui.workbench.texteditor;bundle-version="3.10.0",
  org.eclipse.ui.ide;bundle-version="3.12.0",
  org.eclipse.core.resources;bundle-version="3.11.0",
  org.eclipse.core.expressions;bundle-version="3.6.0",
- org.eclipse.compare;resolution:=optional
+ org.eclipse.compare;bundle-version="3.11.0";resolution:=optional
 Export-Package: org.eclipse.ui.internal.genericeditor;x-internal:=true,
  org.eclipse.ui.internal.genericeditor.hover;x-internal:=true,
  org.eclipse.ui.internal.genericeditor.markers;x-internal:=true,

bundles/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/ExtensionBasedTextViewerConfiguration.java

@@ -19,6 +19,9 @@
  *******************************************************************************/
 package org.eclipse.ui.internal.genericeditor;
 
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.LinkedHashMap;
@@ -138,7 +141,27 @@ public Set<IContentType> getContentTypes(IDocument documentParam) {
 				}
 			}
 		}
-		return this.resolvedContentTypes.isEmpty() ? fallbackContentTypes : resolvedContentTypes;
+		// Try to guess content type based on the content itself, if we don't
+		// have neither a resource, nor file name and no fallback contentTypes
+		if (documentParam != null && this.resolvedContentTypes.isEmpty() && this.fallbackContentTypes.isEmpty()) {
+			String content = documentParam.get();
+			if (content != null && !content.isBlank()) {
+				try (InputStream is = new ByteArrayInputStream(content.getBytes())) {
+					IContentType type = Platform.getContentTypeManager().findContentTypeFor(is, null);
+					while (type != null) {
+						this.resolvedContentTypes.add(type);
+						type = type.getBaseType();
+					}
+				} catch (IOException e) {
+					// silently ignore
+				}
+			}
+		}
+
+		if (this.resolvedContentTypes.isEmpty()) {
+			this.resolvedContentTypes.addAll(this.fallbackContentTypes);
+		}
+		return this.resolvedContentTypes;
 	}
 
 	private static ITextFileBuffer getCurrentBuffer(IDocument document) {
@@ -317,12 +340,17 @@ public IInformationPresenter getInformationPresenter(ISourceViewer sourceViewer)
 				editor, getContentTypes(sourceViewer.getDocument()));
 
 		InformationPresenter presenter = new InformationPresenter(new CompositeInformationControlCreator(hovers));
-		// By default the InformationPresented is set to take the focus when visible,
-		// which makes the Browser to overtake all the focus/mouse etc. control over the
+		// By default the InformationPresented is set to take the focus when
+		// visible,
+		// which makes the Browser to overtake all the focus/mouse etc. control
+		// over the
 		// 'org.eclipse.jface.text.information.InformationPresenter.Closer`.
-		// As we want to make t possible to close the information presenter by clicking
-		// outside of the information control or resizing the editor etc. - we need to
-		// disable such focus overtake by calling `takesFocusWhenVisible(false)` on the
+		// As we want to make t possible to close the information presenter by
+		// clicking
+		// outside of the information control or resizing the editor etc. - we
+		// need to
+		// disable such focus overtake by calling `takesFocusWhenVisible(false)`
+		// on the
 		// presenter.
 		//
 		presenter.takesFocusWhenVisible(false);
@@ -414,8 +442,8 @@ protected IInformationControl doCreateInformationControl(Shell parent) {
 	}
 
 	/**
-	 * Set content-types that will be considered is no content-type can be deduced
-	 * from the document (eg document is not backed by a FileBuffer)
+	 * Set content-types that will be considered is no content-type can be
+	 * deduced from the document (eg document is not backed by a FileBuffer)
 	 */
 	public void setFallbackContentTypes(Set<IContentType> contentTypes) {
 		this.fallbackContentTypes = (contentTypes == null ? Set.of() : contentTypes);

bundles/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/compare/GenericEditorMergeViewer.java

@@ -18,6 +18,7 @@
 
 import org.eclipse.compare.CompareConfiguration;
 import org.eclipse.compare.contentmergeviewer.TextMergeViewer;
+import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.content.IContentType;
 import org.eclipse.jface.preference.IPreferenceStore;
 import org.eclipse.jface.text.IDocument;
@@ -40,6 +41,16 @@ public class GenericEditorMergeViewer extends TextMergeViewer {
 
 	public GenericEditorMergeViewer(Composite parent, CompareConfiguration configuration) {
 		super(parent, configuration);
+		if (configuration != null) {
+			Object id = configuration.getProperty(CompareConfiguration.CONTENT_TYPE);
+			if (id instanceof String contentTypeId) {
+				IContentType contentType = Platform.getContentTypeManager().getContentType(contentTypeId);
+				while (contentType != null) {
+					fallbackContentTypes.add(contentType);
+					contentType = contentType.getBaseType();
+				}
+			}
+		}
 	}
 
 	@Override
@@ -48,8 +59,10 @@ protected SourceViewer createSourceViewer(Composite parent, int textOrientation)
 		res.addTextInputListener(new ITextInputListener() {
 			@Override
 			public void inputDocumentChanged(IDocument oldInput, IDocument newInput) {
-				fallbackContentTypes
-						.addAll(new ExtensionBasedTextViewerConfiguration(null, null).getContentTypes(newInput));
+				if (fallbackContentTypes.isEmpty()) {
+					fallbackContentTypes
+							.addAll(new ExtensionBasedTextViewerConfiguration(null, null).getContentTypes(newInput));
+				}
 				configureTextViewer(res);
 			}