restore cache when content type has been modified

- all opened files in the LSP based editor are added to cache again if
the content is still a C/C++ content.
- clean up API of CLanguageServerEnableCache

bundles/org.eclipse.cdt.lsp/src/org/eclipse/cdt/lsp/internal/server/CLanguageServerEnableCache.java

@@ -43,15 +43,15 @@ public final class CLanguageServerEnableCache implements IContentTypeChangeListe
 
 	private class Data {
 		boolean enable = false;
-		int counter = 0; // reflects the opened LSP based C/C++ Editors for this URI
+		int opened = 0; // reflects the opened LSP based C/C++ Editors for this URI
 
 		private Data(boolean enable) {
 			this.enable = enable;
 		}
 
-		private Data(boolean enable, int counter) {
+		private Data(boolean enable, int opened) {
 			this.enable = enable;
-			this.counter = counter;
+			this.opened = opened;
 		}
 	}
 
@@ -88,10 +88,6 @@ public static void stop() {
 		clearAll();
 	}
 
-	public static void clear() {
-		clearAll();
-	}
-
 	public static synchronized CLanguageServerEnableCache getInstance() {
 		if (instance == null) {
 			instance = new CLanguageServerEnableCache();
@@ -104,8 +100,8 @@ public Boolean get(URI uri) {
 		return data != null ? data.enable : null;
 	}
 
-	public void put(URI uri, boolean value) {
-		cache.put(uri, new Data(value));
+	public void disable(URI uri) {
+		cache.put(uri, new Data(false));
 	}
 
 	@Override
@@ -114,6 +110,15 @@ public void contentTypeChanged(ContentTypeChangeEvent event) {
 		if (C_SOURCE.contentEquals(id) || CXX_SOURCE.contentEquals(id) || C_HEADER.contentEquals(id)
 				|| CXX_HEADER.contentEquals(id)) {
 			clearAll();
+			// add all opened files again if content type is still a C/C++ source or header:
+			LspUtils.getFilesInLspBasedEditor().stream().forEach(uri -> {
+				var data = cache.get(uri);
+				if (data != null) {
+					++data.opened;
+				} else {
+					cache.put(uri, new Data(true, 1));
+				}
+			});
 		}
 	}
 
@@ -134,7 +139,7 @@ public void partClosed(IWorkbenchPart part) {
 			Optional.ofNullable(LSPEclipseUtils.toUri(editor.getEditorInput())).ifPresent(uri -> {
 				var data = cache.get(uri);
 				if (data != null) {
-					if (--data.counter <= 0) {
+					if (--data.opened <= 0) {
 						cache.remove(uri);
 					}
 				}
@@ -154,7 +159,7 @@ public void partOpened(IWorkbenchPart part) {
 				var data = cache.get(uri);
 				if (data != null) {
 					data.enable = true;
-					++data.counter;
+					++data.opened;
 				} else {
 					cache.put(uri, new Data(true, 1));
 				}

bundles/org.eclipse.cdt.lsp/src/org/eclipse/cdt/lsp/internal/server/HasLanguageServerPropertyTester.java

@@ -57,7 +57,7 @@ public boolean test(Object receiver, String property, Object[] args, Object expe
 					return value.booleanValue();
 				}
 				if (!validContentType(uri)) {
-					cache.put(uri, false);
+					cache.disable(uri);
 					return false;
 				}
 				// when getProject is empty, it's an external file: Check if the file is already opened, if not check the active editor:

bundles/org.eclipse.cdt.lsp/src/org/eclipse/cdt/lsp/util/LspUtils.java

@@ -19,7 +19,6 @@
 import java.util.Optional;
 
 import org.eclipse.cdt.lsp.plugin.LspPlugin;
-import org.eclipse.core.internal.content.ContentTypeManager;
 import org.eclipse.core.resources.IFile;
 import org.eclipse.core.resources.IProject;
 import org.eclipse.core.resources.IWorkspace;
@@ -84,6 +83,32 @@ public static boolean isFileOpenedInLspEditor(URI uri) {
 		return false;
 	}
 
+	public static List<URI> getFilesInLspBasedEditor() {
+		var uris = new ArrayList<URI>();
+		var editors = getEditors();
+		if (!editors.isEmpty()) {
+			for (IEditorReference editor : editors) {
+				if (LspPlugin.LSP_C_EDITOR_ID.equals(editor.getId())) {
+					IEditorInput editorInput = null;
+					try {
+						editorInput = editor.getEditorInput();
+					} catch (PartInitException e) {
+						Platform.getLog(LspUtils.class).error(e.getMessage(), e);
+						continue;
+					}
+					if (checkForCContentType(editorInput)) {
+						if (editorInput instanceof IURIEditorInput uriEditorInput) {
+							uris.add(uriEditorInput.getURI());
+						} else if (editorInput instanceof FileEditorInput fileEditorInput) {
+							uris.add(fileEditorInput.getFile().getLocationURI());
+						}
+					}
+				}
+			}
+		}
+		return uris;
+	}
+
 	public static boolean isFileOpenedInLspEditor(IEditorInput editorInput, IContentType contentType) {
 		if (editorInput == null) {
 			return false;
@@ -145,11 +170,9 @@ public static boolean checkForCContentType(IEditorInput editorInput) {
 		} else if (editorInput instanceof FileStoreEditorInput fileStore) {
 			File file = fileStore.getAdapter(File.class);
 			if (file != null) {
-				var contentTypes = ContentTypeManager.getInstance().findContentTypesFor(file.getName());
-				for (var contentType : contentTypes) {
-					if (isCContentType(contentType.getId())) {
-						return true;
-					}
+				var contentType = Platform.getContentTypeManager().findContentTypeFor(file.getName());
+				if (contentType != null) {
+					return isCContentType(contentType.getId());
 				}
 			}
 		}