clang-format: [JS] fix an assertion failure caused by shrinking sources.

Summary:
The JavaScript import sorter has a corner condition that can cause the overall
source text length to shrink. This change circumvents the issue by appending
trailing space in the line after the import blocks to match at least the
previous source code length.

This needs a better long term fix, but this fixes the immediate issue.

Reviewers: alexeagle, djasper

Subscribers: klimek

Differential Revision: http://reviews.llvm.org/D21108

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@272142 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/SortJavaScriptImports.cpp

@@ -170,12 +170,25 @@ public:
     if (ReferencesInOrder && SymbolsInOrder)
       return Result;
 
+    SourceRange InsertionPoint = References[0].Range;
+    InsertionPoint.setEnd(References[References.size() - 1].Range.getEnd());
+
+    // The loop above might collapse previously existing line breaks between
+    // import blocks, and thus shrink the file. SortIncludes must not shrink
+    // overall source length as there is currently no re-calculation of ranges
+    // after applying source sorting.
+    // This loop just backfills trailing spaces after the imports, which are
+    // harmless and will be stripped by the subsequent formatting pass.
+    // TODO: A better long term fix is to re-calculate Ranges after sorting.
+    unsigned PreviousSize = getSourceText(InsertionPoint).size();
+    while (ReferencesText.size() < PreviousSize) {
+      ReferencesText += " ";
+    }
+
     // Separate references from the main code body of the file.
     if (FirstNonImportLine && FirstNonImportLine->First->NewlinesBefore < 2)
       ReferencesText += "\n";
 
-    SourceRange InsertionPoint = References[0].Range;
-    InsertionPoint.setEnd(References[References.size() - 1].Range.getEnd());
     DEBUG(llvm::dbgs() << "Replacing imports:\n"
                        << getSourceText(InsertionPoint) << "\nwith:\n"
                        << ReferencesText << "\n");

unittests/Format/SortImportsTestJS.cpp

@@ -223,6 +223,19 @@ TEST_F(SortImportsTestJS, AffectedRange) {
              24, 30);
 }
 
+TEST_F(SortImportsTestJS, SortingCanShrink) {
+  // Sort excluding a suffix.
+  verifySort("import {B} from 'a';\n"
+             "import {A} from 'b';\n"
+             "\n"
+             "1;",
+             "import {A} from 'b';\n"
+             "\n"
+             "import {B} from 'a';\n"
+             "\n"
+             "1;");
+}
+
 } // end namespace
 } // end namespace format
 } // end namespace clang