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, 26 insertions, 1 deletions

diff --git a/source/slang/slang-diagnostics.cpp b/source/slang/slang-diagnostics.cpp
index 4aabd3ab9..76b2fcffa 100644
--- a/source/slang/slang-diagnostics.cpp
+++ b/source/slang/slang-diagnostics.cpp
@@ -339,12 +339,37 @@ void DiagnosticSink::diagnoseRaw(
     }
 }
 
-
 namespace Diagnostics
 {
 #define DIAGNOSTIC(id, severity, name, messageFormat) const DiagnosticInfo name = { id, Severity::severity, messageFormat };
 #include "slang-diagnostic-defs.h"
 }
 
+DiagnosticInfo const* findDiagnosticByName(UnownedStringSlice const& name)
+{
+    // TODO: We should eventually have a more formal system for associating individual
+    // diagnostics, or groups of diagnostics, with user-exposed names for use when
+    // enabling/disabling warnings (or turning warnings into errors, etc.).
+    //
+    // For now we build an ad hoc mapping from string names to corresponding single
+    // diagnostics (not groups).
+    //
+    static const struct
+    {
+        char const*             name;
+        DiagnosticInfo const*   diagnostic;
+    } kDiagnostics[] =
+    {
+        { "overlapping-bindings", &Diagnostics::parameterBindingsOverlap },
+    };
+
+    for( auto& entry : kDiagnostics )
+    {
+        if( name == entry.name )
+            return entry.diagnostic;
+    }
+    return nullptr;
+}
+
 
 } // namespace Slang