Reflection: allow querying of semantics on varying input/output (#224)

This is functionality required to support a Falcor bug fix.

Most of the code to compute the right semantic name/index for a parameter was already present.
This change adds:

- Storage for semantic name/index on every `VarLayout`
  - Note: this is wasteful and should be optimized later

- A public API to query the semantic name/index
  - The contract is that this API returns `NULL` if the parameter had no semantic

- A bit of work in `parameter-binding.cpp` to attach semantics to varying input/output when traversing varying parameters.
  - Note: this is intentionally set up so that it associates semantics even with non-leaf parameters, so that an API user can query the semantic of a `struct` parameter and know that its members will be assigned sequential semantic indices from its starting value.

- Support for dumping this information in reflection tests

One notable thing that I did *not* change here is that the reflection test fixture doesn't report information on the output of an entry point, even though it really should. That should be fixed in a separate change, though, because it would affect many of the expected outputs.

1 files changed, 13 insertions, 0 deletions

diff --git a/slang.h b/slang.h
index ff79d698b..11b34053c 100644
--- a/slang.h
+++ b/slang.h
@@ -627,6 +627,9 @@ extern "C"
     SLANG_API size_t spReflectionVariableLayout_GetOffset(SlangReflectionVariableLayout* var, SlangParameterCategory category);
     SLANG_API size_t spReflectionVariableLayout_GetSpace(SlangReflectionVariableLayout* var, SlangParameterCategory category);
 
+    SLANG_API char const* spReflectionVariableLayout_GetSemanticName(SlangReflectionVariableLayout* var);
+    SLANG_API size_t spReflectionVariableLayout_GetSemanticIndex(SlangReflectionVariableLayout* var);
+
     // Shader Parameter Reflection
 
     typedef SlangReflectionVariableLayout SlangReflectionParameter;
@@ -989,6 +992,16 @@ namespace slang
         {
             return spReflectionVariableLayout_GetSpace((SlangReflectionVariableLayout*) this, category);
         }
+
+        char const* getSemanticName()
+        {
+            return spReflectionVariableLayout_GetSemanticName((SlangReflectionVariableLayout*) this);
+        }
+
+        size_t getSemanticIndex()
+        {
+            return spReflectionVariableLayout_GetSemanticIndex((SlangReflectionVariableLayout*) this);
+        }
     };
 
     struct EntryPointReflection