Fix assertion in BreakableBlockComment (http://llvm.org/PR21916).

[djasper]

Looks good.

lib/Format/BreakableToken.h

215

nit: The remaining lines' ...

217

nit: .. \c WhitespaceManager. Thus, they ...

lib/Format/BreakableToken.h

private:
   // LeadingWhitespace[i] is the number of characters regarded as whitespace in
   // front of Lines[i]. Note that this can include "* " sequences, which we
   // regard as whitespace when all lines have a "*" prefix.
   SmallVector<unsigned, 16> LeadingWhitespace;
 
   // StartOfLineColumn[i] is the target column at which Line[i] should be.
   // Note that this excludes a leading "* " or "*" in case all lines have
   // a "*" prefix.
+  // The first line's target column is always positive. The rest lines' target
+  // columns are relative to the first line to allow correct indentation of
+  // comments in \c WhitespaceManager, so they can be negative as well (in case
+  // the first line needs to be unindented more than there's actual whitespace
+  // in another line).
   SmallVector<int, 16> StartOfLineColumn;
 
   // The column at which the text of a broken line should start.
   // Note that an optional decoration would go before that column.
   // IndentAtLineBreak is a uniform position for all lines in a block comment,
   // regardless of their relative position.
   // FIXME: Revisit the decision to do this; the main reason was to support
   // patterns like

lib/Format/BreakableToken.cpp

if (Lines[i].empty()) {
       continue;
     }
     // The first line already excludes the star.
     // For all other lines, adjust the line to exclude the star and
     // (optionally) the first whitespace.
     StartOfLineColumn[i] += Decoration.size();
     Lines[i] = Lines[i].substr(Decoration.size());
     LeadingWhitespace[i] += Decoration.size();
-    IndentAtLineBreak = std::min<int>(IndentAtLineBreak, StartOfLineColumn[i]);
+    IndentAtLineBreak =
+        std::min<int>(IndentAtLineBreak, std::max(0, StartOfLineColumn[i]));
   }
   IndentAtLineBreak = std::max<unsigned>(IndentAtLineBreak, Decoration.size());
   DEBUG({
     llvm::dbgs() << "IndentAtLineBreak " << IndentAtLineBreak << "\n";
     for (size_t i = 0; i < Lines.size(); ++i) {
       llvm::dbgs() << i << " |" << Lines[i] << "| " << LeadingWhitespace[i]
                    << "\n";
     }

unittests/Format/FormatTest.cpp

EXPECT_EQ(
       format("#define A \\\nint i;\\\n  int j;", getLLVMStyleWithColumns(11)));
   EXPECT_EQ("template <class T> f();", format("\\\ntemplate <class T> f();"));
 }
 
 TEST_F(FormatTest, NoEscapedNewlineHandlingInBlockComments) {
   EXPECT_EQ("/* \\  \\  \\\n*/", format("\\\n/* \\  \\  \\\n*/"));
 }
 
+TEST_F(FormatTest, DontCrashOnBlockComments) {
+  EXPECT_EQ(
+      "int xxxxxxxxx; /* "
+      "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy\n"
+      "zzzzzz\n"
+      "0*/",
+      format("int xxxxxxxxx;                          /* "
+             "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy zzzzzz\n"
+             "0*/"));
+}
+
 TEST_F(FormatTest, CalculateSpaceOnConsecutiveLinesInMacro) {
   verifyFormat("#define A \\\n"
                "  int v(  \\\n"
                "      a); \\\n"
                "  int i;",
                getLLVMStyleWithColumns(11));
 }