[PATCH] D99495: clang-format: [JS] do not collapse - - to --.

[Martin Probst via Phabricator via cfe-commits]

mprobst created this revision.
mprobst added a reviewer: krasimir.
mprobst requested review of this revision.
Herald added a project: clang.

In JavaScript, `- -1;` is legal syntax, the language allows unary minus.
However the two tokens must not collapse together: `--1` is prefix
decrement, i.e. different syntax.

Before:

- -1; ==> --1;

After:

- -1; ==> - -1;

This change makes no attempt to format this "nicely", given by all
likelihood this represents a programming mistake by the user, or odd
generated code.

The check is not guarded by language: this appears to be a problem in
Java as well, and will also be beneficial when formatting syntactically
incorrect C++ (e.g. during editing).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99495

Files:
  clang/lib/Format/TokenAnnotator.cpp
  clang/unittests/Format/FormatTestJS.cpp


Index: clang/unittests/Format/FormatTestJS.cpp
===================================================================
--- clang/unittests/Format/FormatTestJS.cpp
+++ clang/unittests/Format/FormatTestJS.cpp
@@ -276,6 +276,12 @@
   // ES6 spread operator.
   verifyFormat("someFunction(...a);");
   verifyFormat("var x = [1, ...a, 2];");
+
+  // "- -1" is legal JS syntax, but must not collapse into "--".
+  verifyFormat("- -1;", " - -1;");
+  verifyFormat("-- -1;", " -- -1;");
+  verifyFormat("+ +1;", " + +1;");
+  verifyFormat("++ +1;", " ++ +1;");
 }
 
 TEST_F(FormatTestJS, UnderstandsAmpAmp) {
Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -3370,6 +3370,12 @@
              Style.BitFieldColonSpacing == FormatStyle::BFCS_Before;
     return true;
   }
+  // Do not merge "- -" into "--".
+  if ((Left.isOneOf(tok::minus, tok::minusminus) &&
+       Right.isOneOf(tok::minus, tok::minusminus)) ||
+      (Left.isOneOf(tok::plus, tok::plusplus) &&
+       Right.isOneOf(tok::plus, tok::plusplus)))
+    return true;
   if (Left.is(TT_UnaryOperator)) {
     if (!Right.is(tok::l_paren)) {
       // The alternative operators for ~ and ! are "compl" and "not".


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D99495.333813.patch
Type: text/x-patch
Size: 1309 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20210329/c6ff0a37/attachment.bin>