[clang][Diagnostics] Print empty lines in multiline snippets

[tbaeder]

Summary

We should preserve empty lines in output snippets.

[tbaeder]

clang/test/Misc/diag-style.cpp

10

Questionable whether the space after the | is expected.

[tbaeder]

clang/lib/Frontend/TextDiagnostic.cpp

1246

This is a special case (and probably unneeded?), but otherwise we get 2 empty lines for an empty source line when we print source range info.

[aaron.ballman]

LGTM!

clang/test/Misc/diag-style.cpp

10

I don't have a good intuition for whether it is expected or not, but I think it's defensible.

clang/lib/Frontend/TextDiagnostic.cpp

for (unsigned LineNo = Lines.first; LineNo != Lines.second + 1;
     if (Columns)
       selectInterestingSourceRegion(SourceLine, CaretLine, FixItInsertionLine,
                                     Columns, sourceColMap);
 
     // If we are in -fdiagnostics-print-source-range-info mode, we are trying
     // to produce easily machine parsable output.  Add a space before the
     // source line and the caret to make it trivial to tell the main diagnostic
     // line from what the user is intended to see.
     if (DiagOpts->ShowSourceRanges) {
       SourceLine = ' ' + SourceLine;
       CaretLine = ' ' + CaretLine;
     }
 
     // Emit what we have computed.
     emitSnippet(SourceLine, MaxLineNoDisplayWidth, DisplayLineNo);
 
     if (!CaretLine.empty()) {
void TextDiagnostic::emitSnippetAndCaret(
 
   // Print out any parseable fixit information requested by the options.
   emitParseableFixits(Hints, SM);
 }
 
 void TextDiagnostic::emitSnippet(StringRef SourceLine,
                                  unsigned MaxLineNoDisplayWidth,
                                  unsigned LineNo) {
-  if (SourceLine.empty())
-    return;
-
   // Emit line number.
   if (MaxLineNoDisplayWidth > 0) {
     unsigned LineNoDisplayWidth = getNumDisplayWidth(LineNo);
     OS.indent(MaxLineNoDisplayWidth - LineNoDisplayWidth + 1)
         << LineNo << " | ";
   }
 
   // Print the source line one character at a time.

clang/test/Misc/diag-style.cpp

+// RUN: not %clang_cc1 -fsyntax-only %s 2>&1 | FileCheck -strict-whitespace %s
+
+/// empty lines in multi-line diagnostic snippets are preserved.
+static_assert(false &&
+
+              true, "");
+// CHECK: static assertion failed
+// CHECK-NEXT: {{^}}    4 | static_assert(false &&{{$}}
+// CHECK-NEXT: {{^}}      |               ^~~~~~~~{{$}}
+// CHECK-NEXT: {{^}}    5 | {{$}}
+// CHECK-NEXT: {{^}}    6 |               true, "");{{$}}
+// CHECK-NEXT: {{^}}      |               ~~~~{{$}}