test: [naga wgsl-in] add tests for @must_use

naga/tests/in/must-use-questionable.wgsl

@@ -0,0 +1,44 @@
+fn main() {}
+
+@must_use
+fn use_me(x: i32) -> i32 {
+    return 10 + x;
+}
+
+fn constant_short_circuited_expression() -> bool {
+    return false && 0 != use_me(0);
+}
+
+fn constant_skipped_block() -> i32 {
+    if(false) {
+        return use_me(-1);
+    }
+    return -1;
+}
+
+fn assignment_only() -> i32 {
+    let unused = use_me(-1);
+    return -1;
+}
+
+fn assignment_and_constant_skipped_block() -> i32 {
+    let unused = use_me(-1);
+    if(false) {
+        return unused;
+    }
+    return -1;
+}
+
+fn assignment_and_maybe_skipped_block(skip: bool) -> i32 {
+    let unused = use_me(-1);
+    if(skip) {
+        return unused;
+    }
+    return -1;
+}
+
+fn assign_and_use_before_constant_return() -> i32 {
+    let called_a = use_me(-1);
+    let used_a = 1 + called_a;
+    return 2;
+}

naga/tests/in/must-use.wgsl

@@ -1,15 +1,45 @@
-@compute @workgroup_size(1)
 fn main() {}
 
 @must_use
-fn use_me(x: i32) -> i32 {
-    return 10 + x;
+fn use_me_10() -> i32 { return 10; }
+
+@must_use
+fn use_me_false() -> bool { return false; }
+
+fn use_return() -> i32 {
+    return use_me_10();
+}
+
+fn unused_deep() -> i32 {
+    use_return();
+    return -1;
+}
+
+fn use_in_expression() -> bool {
+    return use_me_10() == 10;
+}
+
+fn assign_and_return() -> i32 {
+    let called_a = use_me_10();
+    return called_a;
+}
+
+fn assign_and_use_before_return() -> i32 {
+    let called_a = use_me_10();
+    let used_a = 1 + called_a;
+    return used_a;
+}
+
+fn assign_and_clobber() -> i32 {
+    var clobber_me = use_me_10();
+    clobber_me = 1000;
+    return clobber_me;
 }
 
-fn useful(
-    m: i32,
-) -> i32 {
-    var q = use_me(m);
-    q += m;
-    return q;
+fn use_in_condition_expression() -> i32 {
+    if(use_me_false()) {
+        return 1;
+    } else {
+        return 2;
+    }
 }