Issue 638 - This is a more comprehensive change to avoid adding dupli…

…cate completions. The real issue is that WordCompletionContributor is invoked automatically by TextMateCompletionContributor, and very often LSP languages are hosted in TextMate-based editors. Now we try to disable WordCompletionContributor by setting a process-level user data value temporarily while collecting completions from other contributors, and the original value is reliably restored (though since the process is transient, that's probably not necessary). If we're able to disable WordCompletionContributor, we just run all remaining completion contributors; if not, we run all remaining completion contributors filtering added completions to exclude duplicate lookup strings. That allow the behavior to degrade gracefully while still yielding an improved signal-to-noise ratio on added completions.

src/main/java/com/redhat/devtools/lsp4ij/features/completion/LSPCompletionContributor.java

@@ -10,15 +10,14 @@
  ******************************************************************************/
 package com.redhat.devtools.lsp4ij.features.completion;
 
-import com.intellij.codeInsight.completion.CompletionContributor;
-import com.intellij.codeInsight.completion.CompletionParameters;
-import com.intellij.codeInsight.completion.CompletionResultSet;
+import com.intellij.codeInsight.completion.*;
 import com.intellij.codeInsight.lookup.*;
 import com.intellij.codeInsight.lookup.impl.LookupImpl;
 import com.intellij.openapi.editor.Document;
 import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.progress.ProcessCanceledException;
 import com.intellij.openapi.progress.ProgressManager;
+import com.intellij.openapi.util.UserDataHolder;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.psi.PsiFile;
 import com.intellij.util.containers.ContainerUtil;
@@ -142,20 +141,45 @@ private void addCompletionItems(@NotNull CompletionParameters parameters,
         }
 
         // If completions were added from LSP and this is auto-completion or the explicit completion trigger was typed
-        // only once, add completions from other contributors carefully to avoid duplicates, specifically from the word
-        // completion contributor
+        // only once, add completions from other all other contributors except for the word completion contributor.
+        // Note that the word completion contributor only really kicks in when LSP completions are added in the context
+        // of a TextMate file (see TextMateCompletionContributor), but that's going to be very common for LSP usage
+        // since it's often adding (pseudo-)language support when not already present in the host JetBrains IDE.
         if ((size > 0) && (parameters.getInvocationCount() < 2)) {
+            // Stop standard processing
             result.stopHere();
-            result.runRemainingContributors(parameters, completionResult -> {
-                LookupElement lookupElement = completionResult.getLookupElement();
-                if (lookupElement != null) {
-                    String lookupString = lookupElement.getLookupString();
-                    if (!addedLookupStrings.contains(lookupString)) {
-                        result.consume(lookupElement);
-                        addedLookupStrings.add(lookupString);
-                    }
+
+            // Try to disable word completion by temporarily setting FORBID_WORD_COMPLETION=true on the completion process
+            CompletionProcess completionProcess = parameters.getProcess();
+            UserDataHolder userDataHolder = completionProcess instanceof UserDataHolder ? (UserDataHolder) completionProcess : null;
+            boolean originalForbidWordCompletion = false;
+            if (userDataHolder != null) {
+                originalForbidWordCompletion = userDataHolder.getUserData(BaseCompletionService.FORBID_WORD_COMPLETION) == Boolean.TRUE;
+                userDataHolder.putUserData(BaseCompletionService.FORBID_WORD_COMPLETION, true);
+            }
+            try {
+                if (userDataHolder != null) {
+                    // If we disabled word completion, just run all remaining contributors
+                    result.runRemainingContributors(parameters, true);
+                } else {
+                    // If not, run all remaining contributors and only add results with distinct lookup strings
+                    result.runRemainingContributors(parameters, completionResult -> {
+                        LookupElement lookupElement = completionResult.getLookupElement();
+                        if (lookupElement != null) {
+                            String lookupString = lookupElement.getLookupString();
+                            if (!addedLookupStrings.contains(lookupString)) {
+                                result.consume(lookupElement);
+                                addedLookupStrings.add(lookupString);
+                            }
+                        }
+                    });
                 }
-            });
+            } finally {
+                // If appropriate, re-enable word completion
+                if (userDataHolder != null) {
+                    userDataHolder.putUserData(BaseCompletionService.FORBID_WORD_COMPLETION, originalForbidWordCompletion);
+                }
+            }
         }
     }