Don't emit interpolation modifiers on struct fields when outputting GLSL

HLSL (and thus Slang) commonly puts interpolation modifiers like `sample` on the fields of `struct` types used as stage input/output, while GLSL only allows them on global-scope `in` and `out` variables (or ones in blocks).

This change emits a really hacky filtering step to skip over certain modifiers when emitting a declaration. This lets us skip interpolation-mode modifiers when outputting a struct field to GLSL.

Note: this probably gets the `in` or `out` block case wrong...

2 files changed, 39 insertions, 4 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 3a5acd024..f5b4a8b56 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -2556,6 +2556,35 @@ struct EmitVisitor
         Emit(";\n");
     }
 
+    bool shouldSkipModifierForDecl(
+        Modifier*   modifier,
+        Decl*       decl)
+    {
+        switch(context->shared->target)
+        {
+        default:
+            break;
+
+        case CodeGenTarget::GLSL:
+            {
+                // Don't emit interpolation mode modifiers on `struct` fields
+                // (only allowed on global or block `in`/`out`)
+                if (auto interpolationMod = dynamic_cast<InterpolationModeModifier*>(modifier))
+                {
+                    if (auto fieldDecl = dynamic_cast<StructField*>(decl))
+                    {
+                        return true;
+                    }
+                }
+
+            }
+            break;
+        }
+
+
+        return false;
+    }
+
     // Emit any modifiers that should go in front of a declaration
     void EmitModifiers(RefPtr<Decl> decl)
     {
@@ -2587,6 +2616,9 @@ struct EmitVisitor
 
         for (auto mod = decl->modifiers.first; mod; mod = mod->next)
         {
+            if (shouldSkipModifierForDecl(mod, decl))
+                continue;
+
             advanceToSourceLocation(mod->Position);
 
             if (0) {}
diff --git a/source/slang/modifier-defs.h b/source/slang/modifier-defs.h
index c401b3353..2b5c77d86 100644
--- a/source/slang/modifier-defs.h
+++ b/source/slang/modifier-defs.h
@@ -208,17 +208,20 @@ SIMPLE_SYNTAX_CLASS(GLSLColumnMajorLayoutModifier, RowMajorLayoutModifier)
 
 // More HLSL Keyword
 
+ABSTRACT_SYNTAX_CLASS(InterpolationModeModifier, Modifier)
+END_SYNTAX_CLASS()
+
 // HLSL `nointerpolation` modifier
-SIMPLE_SYNTAX_CLASS(HLSLNoInterpolationModifier, Modifier)
+SIMPLE_SYNTAX_CLASS(HLSLNoInterpolationModifier, InterpolationModeModifier)
 
 // HLSL `linear` modifier
-SIMPLE_SYNTAX_CLASS(HLSLLinearModifier, Modifier)
+SIMPLE_SYNTAX_CLASS(HLSLLinearModifier, InterpolationModeModifier)
 
 // HLSL `sample` modifier
-SIMPLE_SYNTAX_CLASS(HLSLSampleModifier, Modifier)
+SIMPLE_SYNTAX_CLASS(HLSLSampleModifier, InterpolationModeModifier)
 
 // HLSL `centroid` modifier
-SIMPLE_SYNTAX_CLASS(HLSLCentroidModifier, Modifier)
+SIMPLE_SYNTAX_CLASS(HLSLCentroidModifier, InterpolationModeModifier)
 
 // HLSL `precise` modifier
 SIMPLE_SYNTAX_CLASS(HLSLPreciseModifier, Modifier)