[clang-format] Ignore first token when finding MustBreak

[rymiel]

Summary

When in ColumnLimit 0, the formatter looks for MustBreakBefore in the
line in order to check if a line is allowed to be merged onto one line.

However, since MustBreakBefore is really a property of the gap between
the token and the one previously, I belive the check is erroneous in
checking all the tokens in a line, since whether the previous line ended
with a forced line break should have no effect on whether the current
line is allowed to merge with the next one.

This patch changes the check to skip the first token in
LineJoiner.containsMustBreak.

This patch also changes a test, which is not ideal, but I believe the
test also suffered from this bug. The test case in question sets
AllowShortFunctionsOnASingleLine to "Empty", but the empty function in
said test case isn't merged to a single line, because of the very same
bug this patch fixes.

Fixes https://github.com/llvm/llvm-project/issues/62721

[owenpan]

clang/lib/Format/UnwrappedLineFormatter.cpp

891–895

We can start from the second token.

[rymiel]

Start iteration from second token

clang/lib/Format/UnwrappedLineFormatter.cpp

891–895

Thanks! I'm really glad to have reviewers to catch times where I wasn't thinking straight

[HazardyKnusperkeks]

clang/unittests/Format/FormatTest.cpp

20137

This doesn't seem right.

[rymiel]

clang/unittests/Format/FormatTest.cpp

20137

WhitesmithsBraceStyle.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_Empty; is set above

20137

(this is mentioned in the summary)

[HazardyKnusperkeks]

clang/unittests/Format/FormatTest.cpp

20137

(this is mentioned in the summary)

Sorry about that, I must've skipped that part.

clang/lib/Format/UnwrappedLineFormatter.cpp

private:
   bool nextTwoLinesFitInto(SmallVectorImpl<AnnotatedLine *>::const_iterator I,
                            unsigned Limit) {
     if (I[1]->First->MustBreakBefore || I[2]->First->MustBreakBefore)
       return false;
     return 1 + I[1]->Last->TotalLength + 1 + I[2]->Last->TotalLength <= Limit;
   }
 
   bool containsMustBreak(const AnnotatedLine *Line) {
-    for (const FormatToken *Tok = Line->First; Tok; Tok = Tok->Next)
+    assert(Line->First);
+    // Ignore the first token, because in this situation, it applies more to the
+    // last token of the previous line.
+    for (const FormatToken *Tok = Line->First->Next; Tok; Tok = Tok->Next)
       if (Tok->MustBreakBefore)
         return true;
     return false;
   }
 
   void join(AnnotatedLine &A, const AnnotatedLine &B) {
     assert(!A.Last->Next);
     assert(!B.First->Previous);
     if (B.Affected)

clang/unittests/Format/FormatTest.cpp

EXPECT_EQ("class C {\n"
             "  A() : b(0) {}\n"
             "};",
             format("class C{A():b(0){}};", NoColumnLimit));
   EXPECT_EQ("A()\n"
             "    : b(0) {\n"
             "}",
             format("A()\n:b(0)\n{\n}", NoColumnLimit));
 
+  FormatStyle NoColumnLimitWrapAfterFunction = NoColumnLimit;
+  NoColumnLimitWrapAfterFunction.BreakBeforeBraces = FormatStyle::BS_Custom;
+  NoColumnLimitWrapAfterFunction.BraceWrapping.AfterFunction = true;
+  verifyFormat("class C {\n"
+               "#pragma foo\n"
+               "  int foo { return 0; }\n"
+               "};",
+               NoColumnLimitWrapAfterFunction);
+  verifyFormat("class C {\n"
+               "#pragma foo\n"
+               "  void foo {}\n"
+               "};",
+               NoColumnLimitWrapAfterFunction);
+
   FormatStyle DoNotMergeNoColumnLimit = NoColumnLimit;
   DoNotMergeNoColumnLimit.AllowShortFunctionsOnASingleLine =
       FormatStyle::SFS_None;
   EXPECT_EQ("A()\n"
             "    : b(0) {\n"
             "}",
             format("A():b(0){}", DoNotMergeNoColumnLimit));
   EXPECT_EQ("A()\n"
verifyFormat("void foo() {}\n"
                "#endif",
                WhitesmithsBraceStyle);
 
   verifyFormat("void foobar()\n"
                "  {\n"
                "  int i = 5;\n"
                "  }\n"
                "#ifdef _DEBUG\n"
-               "void bar()\n"
-               "  {\n"
-               "  }\n"
+               "void bar() {}\n"
                "#else\n"
                "void bar()\n"
                "  {\n"
                "  foobar();\n"
                "  }\n"
                "#endif",
                WhitesmithsBraceStyle);