[llvm-bugs] [Bug 34993] New: Syntax error for "new struct" inside conditional-expression

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Oct 18 12:15:50 PDT 2017


            Bug ID: 34993
           Summary: Syntax error for "new struct" inside
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: zeratul976 at hotmail.com
                CC: llvm-bugs at lists.llvm.org

This code does not compile with clang:

struct A {};
struct A* b = (1 == 1) ? new struct A : new struct A;

The error message suggests that it's trying to parse "struct A :" as a
class-specifier, with the ":" starting the base-clause.

I believe that this is valid, at least since DR 2141 [1], which introduced the
"defining-type-specifier" grammar production. A "new-type-id" can only contain
a "type-specifier", not a "defining-type-specifier", and a "class-specifier" is
only valid as a "defining-type-specifier", so I don't believe clang should be
trying to parse a "class-specifier" at all. (Instead, the "struct A" should be
parsed as an "elaborate-type-specifier", which is a valid "type-specifier".)

(I'm not convinced that the code was invalid even before DR 2141 - I would have
thought that, having tried and failed to parse a "class-specifier", the
compiler would backtrack and try to parse an "elaborate-type-specifier" instead
- but I'm less confident about that.)

[1] http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2141

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