Add an attribute to disable the overlapping-bindings warning (#1005)

Currently if the user gives two global shader parameters conflicting bindings, they get a warning diagnostic:

```hlsl
Texture2D a : register(t0);
Texture2D b : register(t0); // WARNING: overlapping bindings
```

This change adds a way to locally disable that warning using an attribute:

```hlsl
[allow("overlapping-bindings")] Texture2D a : register(t0);
[allow("overlapping-bindings")] Texture2D b : register(t0); // OK
```

Note that as a policy decision, the implementation requires `[allow("overlapping-bindings")]` on both declarations in order to disable the warning, under the assumption that the behavior should be strictly opt-in, and not silently affect a programmer who adds a new shader parameter with no knowledge or expectation of possible overlap.

The `[allow(...)]` attribute is intended to be a fairly generally mechanism for disabling optional diagnostics within certain scopes (e.g., for the body of a function definition), but as implemented in this change it is quite restrictive:

* Only the single name `"overlapping-bindings"` will be recognized, and this name cannot be used with, e.g., a `-W` flag on the command line to enable/disable the same diagnostic, or turn it into an error. Adding more cases would be easy enough, but wiring it up to command-line flags could be trickier.

* Only the code that checks for parameter binding overlap is currently checking for `[allow(...)]` attributes, so it is not "wired up" to enable/disable any others. Doing this systematically would ideally involve something in `diagnose()`, but there could be complications to a systematic approach (finding the AST node(s) to use when searching for `[allow(...)]`.

On gotcha here is that versions of Slang without this feature will error out on the `[allow(...)]` attribute since they don't understand it, and if we add future diagnostics that it covers then old compiler versions will (as written) error out on a diagnostic they haven't heard of rather than just assume the `[allow(...)]` attribute doesn't apply to them. These kinds of issues can and should be addressed in future changes.

1 files changed, 38 insertions, 4 deletions

diff --git a/source/slang/slang-parameter-binding.cpp b/source/slang/slang-parameter-binding.cpp
index d5efc3515..dc99f55e2 100644
--- a/source/slang/slang-parameter-binding.cpp
+++ b/source/slang/slang-parameter-binding.cpp
@@ -784,6 +784,25 @@ static UInt allocateUnusedSpaces(
     return context->shared->usedSpaces.Allocate(nullptr, count);
 }
 
+static bool shouldDisableDiagnostic(
+    Decl*                   decl,
+    DiagnosticInfo const&   diagnosticInfo)
+{
+    for( auto dd = decl; dd; dd = dd->ParentDecl )
+    {
+        for( auto modifier : dd->modifiers )
+        {
+            auto allowAttr = as<AllowAttribute>(modifier);
+            if(!allowAttr)
+                continue;
+
+            if(allowAttr->diagnostic == &diagnosticInfo)
+                return true;
+        }
+    }
+    return false;
+}
+
 static void addExplicitParameterBinding(
     ParameterBindingContext*    context,
     RefPtr<ParameterInfo>       parameterInfo,
@@ -842,11 +861,26 @@ static void addExplicitParameterBinding(
             auto paramA = parameterInfo->varLayouts[0]->varDecl.getDecl();
             auto paramB = overlappedVarLayout->varDecl.getDecl();
 
-            getSink(context)->diagnose(paramA, Diagnostics::parameterBindingsOverlap,
-                getReflectionName(paramA),
-                getReflectionName(paramB));
+            auto& diagnosticInfo = Diagnostics::parameterBindingsOverlap;
+
+            // If *both* of the shader parameters declarations agree
+            // that overlapping bindings should be allowed, then we
+            // will not emit a diagnostic. Otherwise, we will warn
+            // the user because such overlapping bindings are likely
+            // to indicate a programming error.
+            //
+            if(shouldDisableDiagnostic(paramA, diagnosticInfo)
+                && shouldDisableDiagnostic(paramB, diagnosticInfo))
+            {
+            }
+            else
+            {
+                getSink(context)->diagnose(paramA, diagnosticInfo,
+                    getReflectionName(paramA),
+                    getReflectionName(paramB));
 
-            getSink(context)->diagnose(paramB, Diagnostics::seeDeclarationOf, getReflectionName(paramB));
+                getSink(context)->diagnose(paramB, Diagnostics::seeDeclarationOf, getReflectionName(paramB));
+            }
         }
     }
 }