clang-format: Break before/between array subscript expressions.

clang-format used to treat array subscript expressions much like
function call (just replacing () with []). However, this is not really
appropriate especially for expressions with multiple subscripts.

Although it might seem counter-intuitive, the most consistent solution
seems to be to always (if necessary) break before a square bracket,
never after it. Also, multiple subscripts of the same expression should
be aligned if they are on subsequent lines.

Before:
  aaaaaaaaaaaaaaaaaaaaaaaaa[aaaaaaaaaaaaaaaaaaaaaaaaa][
      bbbbbbbbbbbbbbbbbbbbbbbbb] = c;
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[
      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa][
      bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = ccccccccccc;

After:
  aaaaaaaaaaaaaaaaaaaaaaaaa[aaaaaaaaaaaaaaaaaaaaaaaaa]
                           [bbbbbbbbbbbbbbbbbbbbbbbbb] = c;
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
      [aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa]
      [bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = ccccccccccc;

llvm-svn: 186153

1 files changed, 23 insertions, 2 deletions

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index a98d565caa4..b1f9f4c85b7 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -334,8 +334,8 @@ private:
           BreakBeforeClosingBrace(false), QuestionColumn(0),
           AvoidBinPacking(AvoidBinPacking), BreakBeforeParameter(false),
           NoLineBreak(NoLineBreak), ColonPos(0), StartOfFunctionCall(0),
-          NestedNameSpecifierContinuation(0), CallContinuation(0),
-          VariablePos(0), ContainsLineBreak(false) {}
+          StartOfArraySubscripts(0), NestedNameSpecifierContinuation(0),
+          CallContinuation(0), VariablePos(0), ContainsLineBreak(false) {}
 
     /// \brief The position to which a specific parenthesis level needs to be
     /// indented.
@@ -381,6 +381,10 @@ private:
     /// \brief The start of the most recent function in a builder-type call.
     unsigned StartOfFunctionCall;
 
+    /// \brief Contains the start of array subscript expressions, so that they
+    /// can be aligned.
+    unsigned StartOfArraySubscripts;
+
     /// \brief If a nested name specifier was broken over multiple lines, this
     /// contains the start column of the second line. Otherwise 0.
     unsigned NestedNameSpecifierContinuation;
@@ -422,6 +426,8 @@ private:
         return ColonPos < Other.ColonPos;
       if (StartOfFunctionCall != Other.StartOfFunctionCall)
         return StartOfFunctionCall < Other.StartOfFunctionCall;
+      if (StartOfArraySubscripts != Other.StartOfArraySubscripts)
+        return StartOfArraySubscripts < Other.StartOfArraySubscripts;
       if (CallContinuation != Other.CallContinuation)
         return CallContinuation < Other.CallContinuation;
       if (VariablePos != Other.VariablePos)
@@ -571,6 +577,12 @@ private:
           State.Column = State.Stack.back().Indent;
           State.Stack.back().ColonPos = State.Column + Current.CodePointCount;
         }
+      } else if (Current.is(tok::l_square) &&
+                 Current.Type != TT_ObjCMethodExpr) {
+        if (State.Stack.back().StartOfArraySubscripts != 0)
+          State.Column = State.Stack.back().StartOfArraySubscripts;
+        else
+          State.Column = ContinuationIndent;
       } else if (Current.Type == TT_StartOfName ||
                  Previous.isOneOf(tok::coloncolon, tok::equal) ||
                  Previous.Type == TT_ObjCMethodExpr) {
@@ -730,6 +742,9 @@ private:
       State.Stack.back().AvoidBinPacking = true;
     if (Current.is(tok::lessless) && State.Stack.back().FirstLessLess == 0)
       State.Stack.back().FirstLessLess = State.Column;
+    if (Current.is(tok::l_square) &&
+        State.Stack.back().StartOfArraySubscripts == 0)
+      State.Stack.back().StartOfArraySubscripts = State.Column;
     if (Current.is(tok::question))
       State.Stack.back().QuestionColumn = State.Column;
     if (!Current.opensScope() && !Current.closesScope())
@@ -835,6 +850,12 @@ private:
       State.Stack.pop_back();
       --State.ParenLevel;
     }
+    if (Current.is(tok::r_square)) {
+      // If this ends the array subscript expr, reset the corresponding value.
+      const FormatToken *NextNonComment = Current.getNextNonComment();
+      if (NextNonComment && NextNonComment->isNot(tok::l_square))
+          State.Stack.back().StartOfArraySubscripts = 0;
+    }
 
     // Remove scopes created by fake parenthesis.
     for (unsigned i = 0, e = Current.FakeRParens; i != e; ++i) {