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.

2 files changed, 24 insertions, 0 deletions

diff --git a/tests/diagnostics/overlapping-bindings.slang b/tests/diagnostics/overlapping-bindings.slang
new file mode 100644
index 000000000..8df588d16
--- /dev/null
+++ b/tests/diagnostics/overlapping-bindings.slang
@@ -0,0 +1,17 @@
+// overlapping-bindings.slang
+
+//DIAGNOSTIC_TEST:SIMPLE:-target hlsl
+
+// Two parameters with the same `register:
+
+Texture2D a : register(t0);
+
+Texture2D b : register(t0);
+
+// Parameters marked to ignore overlap:
+
+[allow("overlapping-bindings")]
+Texture2D c : register(t1);
+
+[allow("overlapping-bindings")]
+Texture2D d : register(t1);
diff --git a/tests/diagnostics/overlapping-bindings.slang.expected b/tests/diagnostics/overlapping-bindings.slang.expected
new file mode 100644
index 000000000..80481eaf9
--- /dev/null
+++ b/tests/diagnostics/overlapping-bindings.slang.expected
@@ -0,0 +1,7 @@
+result code = 0
+standard error = {
+tests/diagnostics/overlapping-bindings.slang(9): warning 39001: explicit binding for parameter 'b' overlaps with parameter 'a'
+tests/diagnostics/overlapping-bindings.slang(7): note: see declaration of 'a'
+}
+standard output = {
+}