clang-format: [JS] do not break location pragma comments.

[mprobst]

Summary

import ... from ...; // from //foo:bar serves as the equivalent if an IWYU
pragma. This change matches // from //.* style comments and never allows them
to wrap, just like IWYU pragmas for C++.

For the time being, it does not seem worth turning this into a configurable
option.

[mprobst]

Abandoning this in favour of the "don't break imports at all" change.

lib/Format/ContinuationIndenter.cpp

unsigned ContinuationIndenter::addMultilineToken(const FormatToken &Current,
   // for all other lines is constant, and we ignore it.
   State.Column = Current.LastLineColumnWidth;
 
   if (ColumnsUsed > getColumnLimit(State))
     return Style.PenaltyExcessCharacter * (ColumnsUsed - getColumnLimit(State));
   return 0;
 }
 
+static llvm::Regex JSImportLocationCommentRegex("^//[ \n\t]*from[ \n\t]+//");
+
 unsigned ContinuationIndenter::breakProtrudingToken(const FormatToken &Current,
                                                     LineState &State,
                                                     bool DryRun) {
   // Don't break multi-line tokens other than block comments. Instead, just
   // update the state.
   if (Current.isNot(TT_BlockComment) && Current.IsMultiline)
     return addMultilineToken(Current, State);
 
Token.reset(new BreakableBlockComment(
         Current, State.Line->Level, StartColumn, Current.OriginalColumn,
         !Current.Previous, State.Line->InPPDirective, Encoding, Style));
   } else if (Current.is(TT_LineComment) &&
              (Current.Previous == nullptr ||
               Current.Previous->isNot(TT_ImplicitStringLiteral))) {
     if (!Style.ReflowComments ||
         CommentPragmasRegex.match(Current.TokenText.substr(2)))
       return 0;
+    if (Style.Language == FormatStyle::LK_JavaScript &&
+        JSImportLocationCommentRegex.match(Current.TokenText))
+      return 0;
+
     Token.reset(new BreakableLineComment(Current, State.Line->Level,
                                          StartColumn, /*InPPDirective=*/false,
                                          Encoding, Style));
     // We don't insert backslashes when breaking line comments.
     ColumnLimit = Style.ColumnLimit;
   } else {
     return 0;
   }

unittests/Format/FormatTestJS.cpp

 
 TEST_F(FormatTestJS, RequoteStringsLeave) {
   FormatStyle LeaveQuotes = getGoogleStyle(FormatStyle::LK_JavaScript);
   LeaveQuotes.JavaScriptQuotes = FormatStyle::JSQS_Leave;
   verifyFormat("var x = \"foo\";", LeaveQuotes);
   verifyFormat("var x = 'foo';", LeaveQuotes);
 }
 
+
+TEST_F(FormatTestJS, LocationComment) {
+  verifyFormat("import {\n"
+               "  x\n"
+               "} from\n"
+               "    'asd';  // from //some/really/long/path/here",
+               "import {x} from 'asd'; // from //some/really/long/path/here",
+               getGoogleJSStyleWithColumns(25));
+}
+
 } // end namespace tooling
 } // end namespace clang