Fail to build with tail cail optimization on Windows

[winapiadmin]

Bug report

Bug description:

Building CPython with tail call optimization makes this error related to tail call optimization:

...
C:\cpython\Python\opcode_targets.h(282,38): error C2085: '_TAIL_CALL_BINARY_OP_SUBSCR_STR_INT': not in formal parameter list [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(283,1): error C2061: syntax error: identifier '__attribute__' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(284,1): error C2143: syntax error: missing ')' before '(' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(284,1): error C2059: syntax error: ')' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(284,21): error C2143: syntax error: missing ')' before 'type' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(284,1): error C2091: function returns function [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(284,38): error C2085: '_TAIL_CALL_BINARY_OP_SUBTRACT_FLOAT': not in formal parameter list [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(285,1): error C2061: syntax error: identifier '__attribute__' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(286,1): error C2143: syntax error: missing ')' before '(' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(286,1): error C2059: syntax error: ')' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(286,21): error C2143: syntax error: missing ')' before 'type' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(286,1): error C2091: function returns function [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(286,38): error C2085: '_TAIL_CALL_BINARY_SLICE': not in formal parameter list [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(287,1): error C2061: syntax error: identifier '__attribute__' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(288,1): error C2143: syntax error: missing ')' before '(' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(288,1): error C2059: syntax error: ')' [C:\cpython\PCbuild\pythoncore.vcxproj]
C:\cpython\Python\opcode_targets.h(288,1): error C1003: error count exceeds 100; stopping compilation [C:\cpython\PCbuild\pythoncore.vcxproj]

While building without it works!

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[sergey-miryanov]

How do you build it?

On 3.14 it fails with message: Tail calling not supported for MSVC.
On main it fails with message: You need at least VS 2026 / PlatformToolset v145 for tail calling.

[chris-eibl]

Tail calling for MSVC is not supported in 3.14 and fails with the given error above on latest 3.14.

#139922 will implement it for 3.15.

@winapiadmin I think we can close this?

[winapiadmin]

probably make it part of 3.14.1 (or 3.15)