Fix integer underflow bug when aligning code in clang-format

[sstwcw]

This isolates the problem that changes the unit test mentioned in https://reviews.llvm.org/D119599.

[HazardyKnusperkeks]

clang/lib/Format/WhitespaceManager.cpp

578

Could you elaborate the problem? Add a test/assert?

clang/unittests/Format/FormatTest.cpp

16854

I disagree. Limit 0 and Limit != 0 behaves differently and you should not remove the old test.

[sstwcw]

clang/unittests/Format/FormatTest.cpp

16854

I hadn't noticed Limit != 0 behaves differently. Now I understand I don't need to change this test. I am going to close this diff.

clang/lib/Format/WhitespaceManager.cpp

for (unsigned j = i + 1; j != e && Changes[j].NewlinesBefore == 0; ++j) {
       // Changes are generally 1:1 with the tokens, but a change could also be
       // inside of a token, in which case it's counted more than once: once for
       // the whitespace surrounding the token (!IsInsideToken) and once for
       // each whitespace change within it (IsInsideToken).
       // Therefore, changes inside of a token should only count the space.
       if (!Changes[j].IsInsideToken)
         LineLengthAfter += Changes[j].TokenLength;
     }
-    unsigned ChangeMaxColumn = Style.ColumnLimit - LineLengthAfter;
+    int ChangeMaxColumn = Style.ColumnLimit - LineLengthAfter;
 
     // If we are restricted by the maximum column width, end the sequence.
     if (ChangeMinColumn > MaxColumn || ChangeMaxColumn < MinColumn ||
         CommasBeforeLastMatch != CommasBeforeMatch) {
       AlignCurrentSequence();
       StartOfSequence = i;
     }
 

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, AlignConsecutiveDeclarations) {
   // Function prototype alignment
   verifyFormat("int    a();\n"
                "double b();",
                Alignment);
   verifyFormat("int    a(int x);\n"
                "double b();",
                Alignment);
   unsigned OldColumnLimit = Alignment.ColumnLimit;
-  // We need to set ColumnLimit to zero, in order to stress nested alignments,
-  // otherwise the function parameters will be re-flowed onto a single line.
-  Alignment.ColumnLimit = 0;
+  // We need to set ColumnLimit to a small number, in order to stress
+  // nested alignments, otherwise the function parameters will be
+  // re-flowed onto a single line. It also needs to be wide enough so
+  // that things still get aligned.
+  Alignment.ColumnLimit = 20;
   EXPECT_EQ("int    a(int   x,\n"
             "         float y);\n"
             "double b(int    x,\n"
             "         double y);",
             format("int a(int x,\n"
                    " float y);\n"
                    "double b(int x,\n"
                    " double y);",