Warn when inout parameter is never written (#4777)

Addresses #4698 as one approach to diagnose the potential problem.

Emit warnings when a user marks a parameter as `inout` but never writes to it in the function. A new intrinsic function `unmodified(out T)` has been added to explicitly indicate that an `inout` variable will not be modified in the function.

This is only one way to address the specific validation error in #4698. In general it seems that DXC does some more extensive checks on actual struct fields (as opposed to observing arbitrary struct writes), so that will be the next step.

1 files changed, 3 insertions, 6 deletions

diff --git a/tests/language-feature/struct-field-initializers/struct-field-no-initializer-complex-types.slang b/tests/language-feature/struct-field-initializers/struct-field-no-initializer-complex-types.slang
index a55c4725d..66a3a2c64 100644
--- a/tests/language-feature/struct-field-initializers/struct-field-no-initializer-complex-types.slang
+++ b/tests/language-feature/struct-field-initializers/struct-field-no-initializer-complex-types.slang
@@ -6,7 +6,7 @@
 //TEST_INPUT:ubuffer(data=[0 0], stride=4):out,name=outputBuffer
 RWStructuredBuffer<int> outputBuffer;
 
-struct DefaultData
+struct DefaultData : IDefaultInitializable
 {
     static const int2 val = int2(0, 1);
     float2 size;
@@ -16,13 +16,10 @@ struct DefaultData
 
 extension DefaultData
 {
-    int someGet()
-    {
-        return val.x;
-    }
+    int someGet() { return val.x; }
 }
 
-int loadDefaultData(inout DefaultData noInit)
+int loadDefaultData(DefaultData noInit)
 {
     outputBuffer[1] = 1;
     return noInit.someGet();