Emit errors for missing returns on unsupported targets (#6633)

* initial wip

* more WIP

* preserve old lower behavior

* remove unnecessary includes

* add test

* add no target case in test

* fix broken test

---------

Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>

2 files changed, 30 insertions, 1 deletions

diff --git a/tests/diagnostics/missing-return-target.slang b/tests/diagnostics/missing-return-target.slang
new file mode 100644
index 000000000..8fc65efd1
--- /dev/null
+++ b/tests/diagnostics/missing-return-target.slang
@@ -0,0 +1,29 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_NOT_SUPP): -entry computeMain -stage compute -target spirv
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_NOT_SUPP): -entry computeMain -stage compute -target glsl
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_NOT_SUPP): -entry computeMain -stage compute -target wgsl
+
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_SUPP):
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_SUPP): -entry computeMain -stage compute -target hlsl
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_SUPP): -entry computeMain -stage compute -target metal
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_SUPP): -entry computeMain -stage compute -target cpp
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK_SUPP): -entry computeMain -stage compute -target cuda
+
+// Some compilation targets allow missing returns while some do not.
+// This test ensures that either errors and warnings are emitted appropriately.
+
+RWStructuredBuffer<uint> out;
+
+// CHECK_NOT_SUPP: warning 41010: non-void function
+// CHECK_NOT_SUPP: error 41009: non-void function
+
+// CHECK_SUPP: warning 41010: non-void function
+
+uint func()
+{
+}
+
+[shader("compute")]
+void computeMain()
+{
+    out[0] = func();
+}
diff --git a/tests/hlsl/tbuffer.slang b/tests/hlsl/tbuffer.slang
index a1bebf2e1..cb014bf2b 100644
--- a/tests/hlsl/tbuffer.slang
+++ b/tests/hlsl/tbuffer.slang
@@ -35,6 +35,6 @@ tbuffer tbuf2 : register(t1)
 
 RWStructuredBuffer<float4> outputBuffer;
 [numthreads(1,1,1)]
-float4 computeMain() {
+void computeMain() {
     outputBuffer[0] = tb_val1 + texture2D[0] + tb_val2;
 }