Fix #pragma warning not working with multifile modules

[Copilot]

The #pragma warning directives were not working correctly when modules included multiple files via __include. Pragma warning states (like disable, push, pop) were being lost when processing subsequent included files, causing warnings to appear even when they should have been suppressed.

Root Cause

The issue was in slang-preprocessor.cpp where a new WarningStateTracker was created for each file processed by the preprocessor. When __include directives processed additional files, they created fresh warning state trackers, losing the pragma warning state from previously processed files.

Example of the Issue

Consider this module structure:

// main.slang
module my_module;
__include "impl1.slang";
__include "impl2.slang";

// impl1.slang  
implementing my_module;
#pragma warning(disable: 30856)
// ... code that should suppress warning 30856

// impl2.slang
implementing my_module; 
// ... code that should still have warning 30856 suppressed

Before this fix, warning 30856 would incorrectly appear in impl2.slang even though it was disabled in impl1.slang.

Solution

Modified the preprocessor to check if the DiagnosticSink already has a WarningStateTracker before creating a new one. This ensures pragma warning states persist across all files in a module:

// Only create a new WarningStateTracker if the sink doesn't already have one.
// This ensures pragma warning states are preserved across included files.
if (!desc.sink->getSourceWarningStateTracker())
{
    preprocessor::WarningStateTracker* wst =
        new preprocessor::WarningStateTracker(desc.sourceManager);
    desc.sink->setSourceWarningStateTracker(wst);
}

Testing

Added comprehensive regression tests covering:

• Multifile modules with pragma warning directives
• Nested __include scenarios
• Single-file pragma warnings (to ensure no regressions)
• Push/pop pragma warning behavior across file boundaries

All existing pragma and warning-related tests continue to pass.

Fixes #7941.

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[CLAassistant]

All committers have signed the CLA.

[kaizhangNV]

LGTM

[jkwak-work]

Wow. I don't understand how it figure it out...

[tdavidovicNV]

@csyonghe this got automatically pulled out of the merge queue for reason I don't fully understand. Seems like the build is just stuck on that machine.