[clang-format] Do not break Objective-C string literals inside array literals

Summary:
Concatenating Objective-C string literals inside an array literal
raises the warning -Wobjc-string-concatenation (which is enabled by default).

clang-format currently splits and concatenates string literals like
the following:

  NSArray *myArray = @[ @"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" ];

into:

  NSArray *myArray =
        @[ @"aaaaaaaaaaaaaaaaaaaaaaaaaaaa"
           @"aaaaaaaaa" ];

which raises the warning. This is https://bugs.llvm.org/show_bug.cgi?id=36153 .

The options I can think of to fix this are:

1) Have clang-format disable Wobjc-string-concatenation by emitting
pragmas around the formatted code
2) Have clang-format wrap the string literals in a macro (which
disables the warning)
3) Disable string splitting for Objective-C string literals inside
array literals

I think 1) has no precedent, and I couldn't find a good
identity() macro for 2). So, this diff implements 3).

Test Plan: make -j12 FormatTests && ./tools/clang/unittests/Format/FormatTests

Reviewers: jolesiak, stephanemoore, djasper

Reviewed By: jolesiak

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D42704

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@324618 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/ContinuationIndenter.cpp

@@ -1285,6 +1285,9 @@ void ContinuationIndenter::moveStatePastScopeOpener(LineState &State,
   State.Stack.back().NestedBlockIndent = NestedBlockIndent;
   State.Stack.back().BreakBeforeParameter = BreakBeforeParameter;
   State.Stack.back().HasMultipleNestedBlocks = Current.BlockParameterCount > 1;
+  State.Stack.back().IsInsideObjCArrayLiteral =
+      Current.is(TT_ArrayInitializerLSquare) && Current.Previous &&
+      Current.Previous->is(tok::at);
 }
 
 void ContinuationIndenter::moveStatePastScopeCloser(LineState &State) {
@@ -1578,6 +1581,11 @@ std::unique_ptr<BreakableToken> ContinuationIndenter::createBreakableToken(
     // likely want to terminate the string before any line breaking is done.
     if (Current.IsUnterminatedLiteral)
       return nullptr;
+    // Don't break string literals inside Objective-C array literals (doing so
+    // raises the warning -Wobjc-string-concatenation).
+    if (State.Stack.back().IsInsideObjCArrayLiteral) {
+      return nullptr;
+    }
 
     StringRef Text = Current.TokenText;
     StringRef Prefix;

lib/Format/ContinuationIndenter.h

@@ -208,7 +208,8 @@ struct ParenState {
         NoLineBreakInOperand(false), LastOperatorWrapped(true),
         ContainsLineBreak(false), ContainsUnwrappedBuilder(false),
         AlignColons(true), ObjCSelectorNameFound(false),
-        HasMultipleNestedBlocks(false), NestedBlockInlined(false) {}
+        HasMultipleNestedBlocks(false), NestedBlockInlined(false),
+        IsInsideObjCArrayLiteral(false) {}
 
   /// \brief The position to which a specific parenthesis level needs to be
   /// indented.
@@ -318,6 +319,10 @@ struct ParenState {
   /// "function" in JavaScript) is not wrapped to a new line.
   bool NestedBlockInlined : 1;
 
+  /// \brief \c true if the current \c ParenState represents an Objective-C
+  /// array literal.
+  bool IsInsideObjCArrayLiteral : 1;
+
   bool operator<(const ParenState &Other) const {
     if (Indent != Other.Indent)
       return Indent < Other.Indent;

unittests/Format/FormatTestObjC.cpp

@@ -975,6 +975,12 @@ TEST_F(FormatTestObjC, ObjCArrayLiterals) {
   verifyFormat("[someFunction someLooooooooooooongParameter:@[\n"
                "  NSBundle.mainBundle.infoDictionary[@\"a\"]\n"
                "]];");
+  Style.ColumnLimit = 20;
+  // We can't break string literals inside NSArray literals
+  // (that raises -Wobjc-string-concatenation).
+  verifyFormat("NSArray *foo = @[\n"
+               "  @\"aaaaaaaaaaaaaaaaaaaaaaaaaa\"\n"
+               "];\n");
 }
 } // end namespace
 } // end namespace format