Improve diagnostics for overlapping/conflicting bindings

Closes #38

- Change overlapping bindings case from error to warning (it is *technically* allowed in HLSL/GLSL)

- Make diagnostic messages for these cases include a note to point at the "other" declaration in each case, so that user can more easily isolate the problem

- Unrelated fix: make sure `slangc` sets up its diagnostic callback *before* parsing command-line options so that error messages output during options parsing will be visible

- Unrelated fix: make sure that formatting for diagnostic messages doesn't print diagnostic ID for notes (all have IDs < 0).
  - Note: eventually I'd like to not print diagnostic IDs at all (I think they are cluttering up our output), but doing that requires touching all the test cases...

2 files changed, 18 insertions, 0 deletions

diff --git a/tests/diagnostics/gh-38-fs.hlsl b/tests/diagnostics/gh-38-fs.hlsl
new file mode 100644
index 000000000..61c8381e4
--- /dev/null
+++ b/tests/diagnostics/gh-38-fs.hlsl
@@ -0,0 +1,9 @@
+//TEST_IGNORE_FILE:
+
+// Companion file to `gh-38-fs.hlsl`
+
+Texture2D overlappingB : register(t0);
+
+Texture2D conflicting : register(t2);
+
+float4 main() : SV_Target { return 0; }
diff --git a/tests/diagnostics/gh-38-vs.hlsl b/tests/diagnostics/gh-38-vs.hlsl
new file mode 100644
index 000000000..7b23efdea
--- /dev/null
+++ b/tests/diagnostics/gh-38-vs.hlsl
@@ -0,0 +1,9 @@
+//TEST:SIMPLE: -target dxbc-assembly -profile vs_5_0 -entry main tests/diagnostics/gh-38-fs.hlsl -profile ps_5_0 -entry main
+
+// Ensure that we catch errors with overlapping or conflicting parameter bindings.
+
+Texture2D overlappingA : register(t0);
+
+Texture2D conflicting : register(t1);
+
+float4 main() : SV_Position { return 0; }