PY-19837 Keep comments before the first import when optimizing imports

They usually serve some specific purpose, e.g. general information
about the module, licence, shebang comment, etc.
Overall, it seems safer to keep them intact.

As suggested in IDEA-CR-19238

python/src/com/jetbrains/python/codeInsight/imports/PyImportOptimizer.java

@@ -28,9 +28,9 @@ import com.intellij.psi.PsiWhiteSpace;
 import com.intellij.psi.codeStyle.CodeStyleManager;
 import com.intellij.psi.codeStyle.CodeStyleSettingsManager;
 import com.intellij.psi.util.PsiTreeUtil;
-import com.intellij.util.ObjectUtils;
-import com.intellij.util.containers.*;
+import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.containers.HashMap;
+import com.intellij.util.containers.MultiMap;
 import com.jetbrains.python.codeInsight.imports.AddImportHelper.ImportPriority;
 import com.jetbrains.python.formatter.PyCodeStyleSettings;
 import com.jetbrains.python.inspections.unresolvedReference.PyUnresolvedReferencesInspection;
@@ -145,7 +145,9 @@ public class PyImportOptimizer implements ImportOptimizer {
         if (fromImport != null && !fromImport.isStarImport()) {
           fromImportSources.putValue(getNormalizedFromImportSource(fromImport), fromImport);
         }
-        precedingComments.putValues(statement, collectPrecedingLineComments(statement));
+        if (statement != myImportBlock.get(0)) {
+          precedingComments.putValues(statement, collectPrecedingLineComments(statement));
+        }
         ContainerUtil.putIfNotNull(statement, as(statement.getLastChild(), PsiComment.class), trailingComments);
       }
       
@@ -231,7 +233,7 @@ public class PyImportOptimizer implements ImportOptimizer {
     private static List<PsiComment> collectPrecedingLineComments(@NotNull PyImportStatementBase statement) {
       final List<PsiComment> result = new ArrayList<>();
       PsiElement prev = PyPsiUtils.getPrevNonWhitespaceSibling(statement);
-      while ((prev instanceof PsiComment) && onItsOwnLine(prev) && !isShebangComment(((PsiComment)prev))) {
+      while (prev instanceof PsiComment && isFirstOnLine(prev)) {
         result.add((PsiComment)prev);
         prev = PyPsiUtils.getPrevNonWhitespaceSibling(prev);
       }
@@ -239,11 +241,7 @@ public class PyImportOptimizer implements ImportOptimizer {
       return result;
     }
 
-    private static boolean isShebangComment(@NotNull PsiComment comment) {
-      return comment.getTextRange().getStartOffset() == 0 && comment.getText().startsWith("#!");
-    }
-
-    private static boolean onItsOwnLine(@NotNull PsiElement element) {
+    private static boolean isFirstOnLine(@NotNull PsiElement element) {
       if (element.getTextRange().getStartOffset() == 0) return true;
       final PsiWhiteSpace sibling = as(PsiTreeUtil.prevLeaf(element), PsiWhiteSpace.class);
       return sibling != null && (sibling.textContains('\n') || sibling.getTextRange().getStartOffset() == 0);
@@ -275,10 +273,8 @@ public class PyImportOptimizer implements ImportOptimizer {
         }
       }
       final PyImportStatementBase firstImport = myImportBlock.get(0);
-      final List<PsiComment> comments = collectPrecedingLineComments(firstImport);
-      final PsiElement topmostAnchor = ObjectUtils.notNull(ContainerUtil.getFirstItem(comments), firstImport);
-      addImportsBefore(topmostAnchor);
-      myFile.deleteChildRange(topmostAnchor, ContainerUtil.getLastItem(myImportBlock));
+      addImportsBefore(firstImport);
+      myFile.deleteChildRange(firstImport, ContainerUtil.getLastItem(myImportBlock));
     }
 
     private void addImportsBefore(@NotNull PsiElement anchor) {

python/testData/optimizeImports/commentsHandling.after.py

@@ -1,7 +1,8 @@
 #!/usr/bin/python
+
+# comment for b
 # comment for a
 import a  # trailing comment for normal import 
-# comment for b
 import b
 # comment for c, d
 import c  # trailing comment for c, d

python/testData/optimizeImports/keepLicenseComment.after.py

@@ -0,0 +1,20 @@
+#!/usr/bin/python
+# Copyright 2000-2017 JetBrains s.r.o.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# specific for import from sys
+from sys import path
+
+from lib import a, b
+
+print(a, b, path)

python/testData/optimizeImports/keepLicenseComment.py

@@ -0,0 +1,20 @@
+#!/usr/bin/python
+# Copyright 2000-2017 JetBrains s.r.o.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from lib import a
+from lib import b
+# specific for import from sys
+from sys import path
+
+print(a, b, path)

python/testSrc/com/jetbrains/python/PyOptimizeImportsTest.java

@@ -249,6 +249,12 @@ public class PyOptimizeImportsTest extends PyTestCase {
     doTest();
   }
 
+  // PY-19837
+  public void testKeepLicenseComment() {
+    getPythonCodeStyleSettings().OPTIMIZE_IMPORTS_JOIN_FROM_IMPORTS_WITH_SAME_SOURCE = true;
+    doTest();
+  }
+
   private void doTest() {
     myFixture.configureByFile(getTestName(true) + ".py");
     OptimizeImportsAction.actionPerformedImpl(DataManager.getInstance().getDataContext(myFixture.getEditor().getContentComponent()));