allow CompletionParameters to have nullable editor

a step towards retrieving completion suggestions from a headless process

platform/lang-api/src/com/intellij/codeInsight/completion/CompletionParameters.java

@@ -16,10 +16,10 @@
 package com.intellij.codeInsight.completion;
 
 import com.intellij.openapi.editor.Editor;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiFile;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * @author peter
@@ -28,12 +28,12 @@ public final class CompletionParameters {
   private final PsiElement myPosition;
   private final PsiFile myOriginalFile;
   private final CompletionType myCompletionType;
-  private final Editor myEditor;
+  @Nullable private final Editor myEditor;
   private final int myOffset;
   private final int myInvocationCount;
 
   CompletionParameters(@NotNull final PsiElement position, @NotNull final PsiFile originalFile,
-                       @NotNull CompletionType completionType, int offset, final int invocationCount, @NotNull Editor editor) {
+                       @NotNull CompletionType completionType, int offset, final int invocationCount, @Nullable Editor editor) {
     assert position.getTextRange().containsOffset(offset) : position;
     myPosition = position;
     assert position.isValid();
@@ -106,8 +106,22 @@ public final class CompletionParameters {
     return myCompletionType == CompletionType.BASIC && myInvocationCount >= 2;
   }
 
+  /**
+   * @return the editor where the completion was started, or null if completion API was invoked in absence of editor.
+   * @see #hasEditor()
+   */
   @NotNull
   public Editor getEditor() {
+    if (myEditor == null) throw new CompletionWithoutEditorException(); 
     return myEditor;
   }
+
+  /** 
+   * @return whether this completion was started within an editor
+   * @since 181.*
+   */
+  public boolean hasEditor() {
+    return myEditor != null;
+  }
+
 }

platform/lang-api/src/com/intellij/codeInsight/completion/CompletionService.java

@@ -77,10 +77,14 @@ public abstract class CompletionService {
 
     for (int i = contributors.indexOf(from) + 1; i < contributors.size(); i++) {
       ProgressManager.checkCanceled();
-      final CompletionContributor contributor = contributors.get(i);
+      CompletionContributor contributor = contributors.get(i);
 
-      final CompletionResultSet result = createResultSet(parameters, consumer, contributor);
-      contributor.fillCompletionVariants(parameters, result);
+      CompletionResultSet result = createResultSet(parameters, consumer, contributor);
+      try {
+        contributor.fillCompletionVariants(parameters, result);
+      }
+      catch (CompletionWithoutEditorException ignore) {
+      }
       if (result.isStopped()) {
         return;
       }

platform/lang-api/src/com/intellij/codeInsight/completion/CompletionWithoutEditorException.java

@@ -0,0 +1,12 @@
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.codeInsight.completion;
+
+/**
+ * An exception thrown when a completion contributor attempts to invoke {@link CompletionParameters#getEditor()}
+ * for a completion performed in absence of editor. This exception is caught by completion infrastructure, and so
+ * shouldn't be handled by contributors. To avoid this exception, check {@link CompletionParameters#hasEditor()}.
+ * 
+ * @since 181.*
+ */
+public class CompletionWithoutEditorException extends RuntimeException {
+}