Scope the base_macros.h warning disables to base.h

[Daniel Jump (DanielJump)]

Fixes #1624.

base_macros.h disables C5046, C4268, C4499 and C4630 with no matching #pragma warning(push) / (pop). base.h includes it near the top and never restores the warning state, so those four warnings stay disabled for the rest of every translation unit that includes <winrt/base.h> - the consumer's own code included.

namespace { struct S { int x; }; }
S f();
int main() { f(); return 0; }

warns C5046 on its own, and goes silent as soon as <winrt/base.h> is included ahead of it, at both /W4 and /Wall.

Change

Open the warning scope immediately before the base_macros.h include in write_base_h and close it at the end of the file, using the existing finish_with / wrap_* idiom so the pop cannot be forgotten. The disables still cover every declaration C++/WinRT makes, which is what they were added for; only their escape into consumer code is removed.

base_macros.h itself keeps the disables, with a comment recording that the enclosing scope belongs to the including file, so the pairing is discoverable from either side.

Validation

Applied the equivalent change to a shipped winrt/base.h and rebuilt with the Windows SDK headers, MSVC x64, /std:c++20 /permissive- /Wall:

• consumer C5046 in the repro above: suppressed before, reported after
• no C4193 (warning(pop) with no matching push)
• a translation unit exercising collections, coroutines, delegates, implements, factories and classic COM reports an identical 166 warnings before and after (C5246 x114, C4365 x21, C4946 x16, C4265 x15), so nothing inside the C++/WinRT headers regressed

Not changed

base_macros.h is also root-included by the generated component .g.h files under WINRT_IMPORT_MODULE and by the global module fragment of each generated .ixx. Those are cppwinrt's own module builds rather than ordinary consumer translation units, and C4499 / C4630 are wanted there, so I left those paths alone. Happy to extend this if you would rather it were uniform.

[Copilot]

🟢 Approval recommended

The change safely scopes MSVC warning disables to the generated header and is low risk, with only a minor comment-accuracy nit noted.

Pull request overview

This PR fixes warning-state leakage from <winrt/base.h> by scoping the MSVC warning disables originating in base_macros.h so they apply to C++/WinRT’s own declarations but don’t remain disabled for downstream consumer code.

Changes:

• Add a generator-emitted #pragma warning(push) immediately before base_macros.h is included in the generated base.h.
• Ensure a matching #pragma warning(pop) is emitted at the end of the generated base.h via the existing finish_with RAII writer pattern.
• Document the intended pairing behavior in strings/base_macros.h.

File summaries

File	Description
strings/base_macros.h	Adds commentary explaining intended warning-disable scoping behavior for MSVC.
cppwinrt/file_writers.h	Wraps the base_macros root-include in a push/pop warning scope when generating winrt/base.h.
cppwinrt/code_writers.h	Introduces a reusable writer RAII helper that emits #pragma warning(push) and guarantees a matching pop.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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