Add warning for returning without initializing out parameter (#2807)

* Add warning for returning without initializing out parameter

* Add unused prelude function to squash uninitialized out variable warnings

2 files changed, 63 insertions, 1 deletions

diff --git a/tests/diagnostics/uninitialized-out.slang b/tests/diagnostics/uninitialized-out.slang
index c285970da..d0d87449f 100644
--- a/tests/diagnostics/uninitialized-out.slang
+++ b/tests/diagnostics/uninitialized-out.slang
@@ -2,6 +2,56 @@
 
 float foo(out float3 v)
 {
+    // This should error as we haven't set v before we read from it
     float r = v.x + 1.0;
+    // This should warn as we haven't set v before we return
     return r;
 }
+
+// This should warn as we return without x being initialized
+float bar(out float x)
+{
+    return 0;
+}
+
+// This should also warn pointing at the implicit return
+void baz(out float x) {}
+
+void twoReturns(bool b, out float y)
+{
+    if(b)
+    {
+        // Should warn
+        return;
+    }
+    y = 0;
+    // Shouldn't warn
+    return;
+}
+
+void twoOkReturns(bool b, out float y)
+{
+    if(b)
+    {
+        // Shouldn't warn
+        unused(y);
+        return;
+    }
+    y = 0;
+    // Shouldn't warn
+    return;
+}
+
+// TODO: This should warn that n is potentially uninitialized
+int ok(bool b, out int n)
+{
+    if(b)
+        n = 0;
+    return n;
+}
+
+// TODO: This should warn that arr isn't fully initialized
+void partial(out float arr[2])
+{
+    arr[0] = 1;
+}
diff --git a/tests/diagnostics/uninitialized-out.slang.expected b/tests/diagnostics/uninitialized-out.slang.expected
index feb8c494a..5846c12df 100644
--- a/tests/diagnostics/uninitialized-out.slang.expected
+++ b/tests/diagnostics/uninitialized-out.slang.expected
@@ -1,8 +1,20 @@
 result code = -1
 standard error = {
-tests/diagnostics/uninitialized-out.slang(5): error 41015: use of uninitialized value.
+tests/diagnostics/uninitialized-out.slang(6): error 41015: use of uninitialized value 'v'
     float r = v.x + 1.0;
                 ^
+tests/diagnostics/uninitialized-out.slang(8): warning 41016: returning without initializing out parameter 'v'
+    return r;
+    ^~~~~~
+tests/diagnostics/uninitialized-out.slang(14): warning 41016: returning without initializing out parameter 'x'
+    return 0;
+    ^~~~~~
+tests/diagnostics/uninitialized-out.slang(18): warning 41016: returning without initializing out parameter 'x'
+void baz(out float x) {}
+                       ^
+tests/diagnostics/uninitialized-out.slang(25): warning 41016: returning without initializing out parameter 'y'
+        return;
+        ^~~~~~
 }
 standard output = {
 }