Fix l-value computation for subscript call. (#5177)

2 files changed, 48 insertions, 0 deletions

diff --git a/tests/bugs/gh-4971-2.slang b/tests/bugs/gh-4971-2.slang
new file mode 100644
index 000000000..78efded79
--- /dev/null
+++ b/tests/bugs/gh-4971-2.slang
@@ -0,0 +1,23 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+
+struct Test {
+    RWStructuredBuffer<int> val;
+    __subscript(int x, int y)->int
+    {
+        get { return val[x * 3 + y]; }
+        set { val[x * 3 + y] = newValue; }
+    }
+}
+Test test;
+
+[numthreads(1, 1, 1)]
+void computeMain()
+{
+    // test[0,0] is not an l-value because `test` is a read-only parameter,
+    // and the `set` accessor is by-default `mutating`, which means that it is
+    // only callable when `test` itself is l-value.
+    
+    // CHECK: ([[# @LINE+1]]): error 30011
+    test[0,0] = 1;
+
+}
\ No newline at end of file
diff --git a/tests/bugs/gh-4971.slang b/tests/bugs/gh-4971.slang
new file mode 100644
index 000000000..948e43385
--- /dev/null
+++ b/tests/bugs/gh-4971.slang
@@ -0,0 +1,25 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK):-vk -output-using-type
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK):-d3d11 -output-using-type
+
+struct Test {
+    RWStructuredBuffer<int> val;
+    __subscript(int x, int y)->int
+    {
+        get { return val[x * 3 + y]; }
+        [nonmutating] set { val[x * 3 + y] = newValue; }
+    }
+}
+Test test;
+
+//TEST_INPUT: set test = {out ubuffer(data=[0 0 0 0 0 0 0 0 0], stride=4)};
+
+[numthreads(1, 1, 1)]
+void computeMain()
+{
+    // test[0,0] should be a valid l-value here because although `test` is
+    // a read-only parameter, the `set` accessor is marked as `nonmutating`,
+    // which means that it can be called even when `test` is not mutable.
+
+    // CHECK: 1
+    test[0,0] = 1;
+}
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