[clang-format] Don't align too long broken trailing comments

[krasimir]

Summary

This patch fixes a bug where clang-format will align newly broken trailing
comments even if this will make them exceed the line limit. The bug was caused
by a combination of unsigned arithmetic overflow and an imprecise computation
of the length of broken comment lines.

[alexfh]

LG

[pboettch]

Could this be, that this commit doesn't handle well ColumnLimit: 0? With my style based on LLVM and ColumnLimit: 0 I had comments and consecutive lines aligned before, not anymore with

clang-format version 5.0.0-+rc2-1 (tags/RELEASE_500/rc2)

from Debian testing.

[krasimir]

@pboettch: It's possible. Please file a bug with an example.

[pboettch]

This is my proposal to fix it: https://reviews.llvm.org/D36967

lib/Format/WhitespaceManager.cpp

unsigned PreviousOriginalWhitespaceEnd = SourceMgr.getFileOffset(
         Changes[i - 1].OriginalWhitespaceRange.getEnd());
     Changes[i - 1].TokenLength = OriginalWhitespaceStart -
                                  PreviousOriginalWhitespaceEnd +
                                  Changes[i].PreviousLinePostfix.size() +
                                  Changes[i - 1].CurrentLinePrefix.size();
 
     // If there are multiple changes in this token, sum up all the changes until
     // the end of the line.
-    if (Changes[i - 1].IsInsideToken)
+    if (Changes[i - 1].IsInsideToken && Changes[i - 1].NewlinesBefore == 0)
       LastOutsideTokenChange->TokenLength +=
           Changes[i - 1].TokenLength + Changes[i - 1].Spaces;
     else
       LastOutsideTokenChange = &Changes[i - 1];
 
     Changes[i].PreviousEndOfTokenColumn =
         Changes[i - 1].StartOfTokenColumn + Changes[i - 1].TokenLength;
 
void WhitespaceManager::alignTrailingComments() {
   for (unsigned i = 0, e = Changes.size(); i != e; ++i) {
     if (Changes[i].StartOfBlockComment)
       continue;
     Newlines += Changes[i].NewlinesBefore;
     if (!Changes[i].IsTrailingComment)
       continue;
 
     unsigned ChangeMinColumn = Changes[i].StartOfTokenColumn;
-    unsigned ChangeMaxColumn = Style.ColumnLimit - Changes[i].TokenLength;
+    unsigned ChangeMaxColumn = Style.ColumnLimit >= Changes[i].TokenLength
+                                   ? Style.ColumnLimit - Changes[i].TokenLength
+                                   : ChangeMinColumn;
 
     // If we don't create a replacement for this change, we have to consider
     // it to be immovable.
     if (!Changes[i].CreateReplacement)
       ChangeMaxColumn = ChangeMinColumn;
 
     if (i + 1 != e && Changes[i + 1].ContinuesPPDirective)
       ChangeMaxColumn -= 2;

unittests/Format/FormatTestComments.cpp

EXPECT_EQ("int ab; // line\n"
             "\n"
             "// long",
             format("int ab; // line\n"
                    "int a; // long long\n"
                    "\n"
                    "// long",
                    getLLVMStyleWithColumns(15)));
 
+  // Don't align newly broken trailing comments if that would put them over the
+  // column limit.
+  EXPECT_EQ("int i, j; // line 1\n"
+            "int k; // line longg\n"
+            "       // long",
+            format("int i, j; // line 1\n"
+                   "int k; // line longg long",
+                   getLLVMStyleWithColumns(20)));
+
   // Align comment line sections aligned with the next token with the next
   // token.
   EXPECT_EQ("class A {\n"
             "public: // public comment\n"
             "  // comment about a\n"
             "  int a;\n"
             "};",
             format("class A {\n"