Fix DebugGlobalVariable source file assignment for included/imported files

[Copilot]

DebugGlobalVariable for synthesized entry point parameters (e.g., input_texCoord, entryPointParam_main) incorrectly references included/imported files instead of the main shader file.

Changes

• SPIRV emit: Pre-scan entry points to extract their IRDebugLocationDecoration source and use it as the preferred m_defaultDebugSource
• SPIRV emit: Only fall back to non-included files when no entry point source is available
• IR linking: Mark DebugSource from imported modules as included during cloning
• Lower-to-IR: Mark dynamically loaded sources via getOrEmitDebugSource as included

Root Cause

For import syntax, imported modules are compiled separately with their DebugSource having isIncludedFile=false. When linked, this flag is preserved, causing the imported module's source to potentially become m_defaultDebugSource.

Example

Before fix:

%4 = OpExtInst %void %2 DebugSource %5 %1   ; shader-utils-module.slang
%14 = OpExtInst %void %2 DebugSource %15 %13 ; main.slang
%76 = OpExtInst %void %2 DebugGlobalVariable ... %4 ...  ; Wrong: references imported file

After fix:

%76 = OpExtInst %void %2 DebugGlobalVariable ... %14 ...  ; Correct: references main file

Tests Added

• tests/spirv/debug-global-variable-source.slang (#include case)
• tests/spirv/debug-global-variable-source-import.slang (import case)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Source of DebugGlobalVariable is set to the wrong slang file</issue_title>
<issue_description># Issue Description
When the slang shader includes a header file, for global variable in the main slang file, Source of DebugGlobalVariable is set to the header file, which is wrong.

Reproducer Code

modular_slang_shader.slang

#include "shader_utils.slang"

struct VertexOutput
{
    float4 position : SV_Position;
    float2 texCoord : TEXCOORD0;
}

[shader("fragment")]
float4 main(VertexOutput input) : SV_Target
{
    // Create a simple gradient pattern based on texture coordinates
    float2 uv = input.texCoord;
    
    // Call function from the included header file
    float distanceFromCenter = calculateDistanceFromCenter(uv);
    
    // Use another function from the header for a radial fade effect
    float radialFade = createRadialFade(uv, 0.7);
    
    // Create color pattern with both distance effects
    float4 color = float4(
        uv.x * (1.0 - distanceFromCenter * 0.5),  // Red with subtle distance fade
        uv.y * radialFade,                        // Green with smooth radial fade
        uv.x * uv.y,                             // Blue as product of coordinates
        1.0                                      // Full opacity
    );
    
    return color;
}

shader_utils.slang

#ifndef SHADER_UTILS_SLANG
#define SHADER_UTILS_SLANG

// Helper function to calculate distance from center
float calculateDistanceFromCenter(float2 uv)
{
    float2 center = float2(0.5, 0.5);
    return length(uv - center);
}

// Additional utility function - simple smoothstep fade
float createRadialFade(float2 uv, float radius)
{
    float dist = calculateDistanceFromCenter(uv);
    return smoothstep(radius, 0.0, dist);
}

#endif // SHADER_UTILS_SLANG

With "slangc.exe modular_slang_shader.slang -target spirv-asm -gdwarf -g3 -O0 -line-directive-mode glsl -stage fragment -o modular_slang_shader_g2_o0_non_sem.spvasm -entry main -fvk-b-shift 0 0", in the generated modular_slang_shader_g2_o0_non_sem.spvasm file, we have:

; Debug Information
%1 = OpString "#ifndef SHADER_UTILS_SLANG
#define SHADER_UTILS_SLANG

// Helper function to calculate distance from center
float calculateDistanceFromCenter(float2 uv)
...
#endif // SHADER_UTILS_SLANG
"
%5 = OpString "D:\p4\bugfix_main\out_nvn2\wddm2_amd64_debug\shader_utils.slang"
%6 = OpString "#include "shader_utils.slang"

struct VertexOutput
{
float4 position : SV_Position;
float2 texCoord : TEXCOORD0;
}
...
"
%8 = OpString "D:\p4\bugfix_main\out_nvn2\wddm2_amd64_debug\modular_slang_shader.slang"
...
%4 = OpExtInst %void %2 DebugSource %5 %1
%7 = OpExtInst %void %2 DebugSource %8 %6
...
%input_texCoord = OpVariable %_ptr_Input_v2float Input ; Location 0
%70 = OpExtInst %void %2 DebugGlobalVariable %71 %51 %4 %uint_0 %uint_0 %13 %71 %%uint_0
%entryPointParam_main = OpVariable %_ptr_Output_v4float Output ; Location 0
%182 = OpExtInst %void %2 DebugGlobalVariable %183 %46 %4 %uint_0 %uint_0 %13 %183 %entryPointParam_main %uint_0

Expected Behavior

Source of DebugGlobalVariable (input_texCoord, entryPointParam_main) should be %7, the main slang shader file.

Actual Behavior

Source of DebugGlobalVariable is %4, the included shader file.

Environment

• Slang Version (v2025.17.1)
• OS (Windows)

Additional context

The source file for global variable is still wrong after #7923 is fixed.
</issue_description>

Comments on the Issue (you are @copilot in this section)

@lujinwangnv @claude Could you help investigate and fix the issue? @lujinwangnv @claude help: would your current fix take care of global variables in the included file? would the source of DebugGlobalVariable for those global variables be the included file? @lujinwangnv @claude help: can you investigate into the AST-to-IR lowering phase where IRDebugLocationDecoration is initially assigned to root-cause the issue? @lujinwangnv I checked the change AI proposed, it might not work for all cases. Need some local testing and debugging to verify the change. @lujinwangnv This issue and https://github.com//issues/7923 (fixed with PR https://github.com//pull/7957, closed) both still repro with import ed files. @zangold-nv Assigning copilot to see if it can extend the fixes for this issue and issue #7923 to cover the `import "shader_utils.slang";` syntax case.

• Fixes Source of DebugGlobalVariable is set to the wrong slang file #8582

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