do not indent if caret is currently at beginning of line (PY-3009)

python/src/META-INF/python-plugin-common.xml

@@ -34,6 +34,7 @@
     <backspaceHandlerDelegate implementation="com.jetbrains.python.editor.PythonBackspaceHandler"/>
     <quoteHandler fileType="Python" className="com.jetbrains.python.editor.PythonQuoteHandler"/>
     <enterHandlerDelegate implementation="com.jetbrains.python.editor.PythonEnterHandler"/>
+    <enterHandlerDelegate implementation="com.jetbrains.python.editor.PyEnterAtIndentHandler" order="first"/>
     <enterHandlerDelegate implementation="com.jetbrains.python.editor.PyEnterBetweenBracketsHandler"/>
     <sdkType implementation="com.jetbrains.python.sdk.PythonSdkType"/>
     <gotoClassContributor implementation="com.jetbrains.python.PyGotoClassContributor"/>

python/src/com/jetbrains/python/editor/PyEnterAtIndentHandler.java

@@ -0,0 +1,42 @@
+package com.jetbrains.python.editor;
+
+import com.intellij.codeInsight.editorActions.BackspaceHandler;
+import com.intellij.codeInsight.editorActions.enter.EnterHandlerDelegateAdapter;
+import com.intellij.injected.editor.EditorWindow;
+import com.intellij.openapi.actionSystem.DataContext;
+import com.intellij.openapi.editor.Editor;
+import com.intellij.openapi.editor.actionSystem.EditorActionHandler;
+import com.intellij.openapi.util.Ref;
+import com.intellij.psi.PsiFile;
+import com.intellij.psi.impl.source.tree.injected.InjectedLanguageUtil;
+import com.jetbrains.python.psi.PyFile;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * @author yole
+ */
+public class PyEnterAtIndentHandler extends EnterHandlerDelegateAdapter {
+  @Override
+  public Result preprocessEnter(@NotNull PsiFile file,
+                                @NotNull Editor editor,
+                                @NotNull Ref<Integer> caretOffset,
+                                @NotNull Ref<Integer> caretAdvance,
+                                @NotNull DataContext dataContext,
+                                EditorActionHandler originalHandler) {
+    int offset = caretOffset.get();
+    if (editor instanceof EditorWindow) {
+      file = InjectedLanguageUtil.getTopLevelFile(file);
+      editor = InjectedLanguageUtil.getTopLevelEditor(editor);
+      offset = editor.getCaretModel().getOffset();
+    }
+    if (!(file instanceof PyFile)) {
+      return Result.Continue;
+    }
+
+    // honor dedent (PY-3009)
+    if (BackspaceHandler.isWhitespaceBeforeCaret(editor)) {
+      return Result.DefaultSkipIndent;
+    }
+    return Result.Continue;
+  }
+}

python/src/com/jetbrains/python/editor/PythonEnterHandler.java

@@ -65,7 +65,7 @@ public class PythonEnterHandler extends EnterHandlerDelegateAdapter {
     if (isSplitLine != null) {
       return Result.Continue;
     }
-    Document doc = editor.getDocument();
+    final Document doc = editor.getDocument();
     PsiDocumentManager.getInstance(file.getProject()).commitDocument(doc);
     final PsiElement element = file.findElementAt(offset);
     CodeInsightSettings codeInsightSettings = CodeInsightSettings.getInstance();
@@ -145,6 +145,14 @@ public class PythonEnterHandler extends EnterHandlerDelegateAdapter {
     if (!PyCodeInsightSettings.getInstance().INSERT_BACKSLASH_ON_WRAP) {
       return Result.Continue;
     }
+    return checkInsertBackslash(file, caretOffset, dataContext, offset, doc);
+  }
+
+  private static Result checkInsertBackslash(PsiFile file,
+                                             Ref<Integer> caretOffset,
+                                             DataContext dataContext,
+                                             int offset,
+                                             Document doc) {
     if (offset > 0) {
       final PsiElement beforeCaret = file.findElementAt(offset - 1);
       if (beforeCaret instanceof PsiWhiteSpace && beforeCaret.getText().indexOf('\\') >= 0) {

python/testSrc/com/jetbrains/python/PyIndentTest.java

@@ -303,6 +303,16 @@ public class PyIndentTest extends PyTestCase {
            "     <caret>)");
   }
 
+  public void testRespectDedent() {  // PY-3009
+    doTest("if True:\n" +
+           "    bar\n" +
+           "<caret>",
+           "if True:\n" +
+           "    bar\n" +
+           "\n" +
+           "<caret>");
+  }
+
   /*
   TODO: formatter core problem?
   public void testAlignListBeforeEquals() throws Exception {