tint: Deprecated module-scope 'let' for 'const'

Enable the parsing of 'const'.
Warn on use of module-scope 'let', and automatically replace with 'const'.

Fixed: tint:1580
Change-Id: I214aabca80686dc6b60ae21a7a57fbfb4898ea83
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/93786
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/transform/loop_to_for_loop_test.cc

@@ -151,7 +151,7 @@ fn f() {
 )";
 
     auto* expect = R"(
-let N = 16u;
+const N = 16u;
 
 fn f() {
   var i : u32 = 0u;

src/tint/transform/promote_initializers_to_let_test.cc

@@ -1099,20 +1099,16 @@ struct S1 {
 
 TEST_F(PromoteInitializersToLetTest, NoChangeOnVarDecl) {
     auto* src = R"(
-struct S {
-  a : i32,
-  b : f32,
-  c : i32,
-}
+type F = f32;
 
 fn f() {
   var local_arr = array<f32, 4u>(0.0, 1.0, 2.0, 3.0);
-  var local_str = S(1, 2.0, 3);
+  var local_str = F(3.0);
 }
 
-let module_arr : array<f32, 4u> = array<f32, 4u>(0.0, 1.0, 2.0, 3.0);
+const module_arr : array<f32, 4u> = array<f32, 4u>(0.0, 1.0, 2.0, 3.0);
 
-let module_str : S = S(1, 2.0, 3);
+const module_str : F = F(2.0);
 )";
 
     auto* expect = src;
@@ -1127,18 +1123,14 @@ TEST_F(PromoteInitializersToLetTest, NoChangeOnVarDecl_OutOfOrder) {
     auto* src = R"(
 fn f() {
   var local_arr = array<f32, 4u>(0.0, 1.0, 2.0, 3.0);
-  var local_str = S(1, 2.0, 3);
+  var local_str = F(3.0);
 }
 
-let module_str : S = S(1, 2.0, 3);
+const module_str : F = F(2.0);
 
-struct S {
-  a : i32,
-  b : f32,
-  c : i32,
-}
+type F = f32;
 
-let module_arr : array<f32, 4u> = array<f32, 4u>(0.0, 1.0, 2.0, 3.0);
+const module_arr : array<f32, 4u> = array<f32, 4u>(0.0, 1.0, 2.0, 3.0);
 )";
 
     auto* expect = src;

src/tint/transform/robustness_test.cc

@@ -21,7 +21,7 @@ namespace {
 
 using RobustnessTest = TransformTest;
 
-TEST_F(RobustnessTest, Array_Idx_Clamp) {
+TEST_F(RobustnessTest, Array_Let_Idx_Clamp) {
     auto* src = R"(
 var<private> a : array<f32, 3>;
 
@@ -35,7 +35,7 @@ fn f() {
     auto* expect = R"(
 var<private> a : array<f32, 3>;
 
-let c : u32 = 1u;
+const c : u32 = 1u;
 
 fn f() {
   let b : f32 = a[1u];
@@ -47,7 +47,33 @@ fn f() {
     EXPECT_EQ(expect, str(got));
 }
 
-TEST_F(RobustnessTest, Array_Idx_Clamp_OutOfOrder) {
+TEST_F(RobustnessTest, Array_Const_Idx_Clamp) {
+    auto* src = R"(
+var<private> a : array<f32, 3>;
+
+const c : u32 = 1u;
+
+fn f() {
+  let b : f32 = a[c];
+}
+)";
+
+    auto* expect = R"(
+var<private> a : array<f32, 3>;
+
+const c : u32 = 1u;
+
+fn f() {
+  let b : f32 = a[1u];
+}
+)";
+
+    auto got = Run<Robustness>(src);
+
+    EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(RobustnessTest, Array_Let_Idx_Clamp_OutOfOrder) {
     auto* src = R"(
 fn f() {
   let b : f32 = a[c];
@@ -63,7 +89,33 @@ fn f() {
   let b : f32 = a[1u];
 }
 
-let c : u32 = 1u;
+const c : u32 = 1u;
+
+var<private> a : array<f32, 3>;
+)";
+
+    auto got = Run<Robustness>(src);
+
+    EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(RobustnessTest, Array_Const_Idx_Clamp_OutOfOrder) {
+    auto* src = R"(
+fn f() {
+  let b : f32 = a[c];
+}
+
+const c : u32 = 1u;
+
+var<private> a : array<f32, 3>;
+)";
+
+    auto* expect = R"(
+fn f() {
+  let b : f32 = a[1u];
+}
+
+const c : u32 = 1u;
 
 var<private> a : array<f32, 3>;
 )";
@@ -1392,7 +1444,7 @@ struct S {
 
 @group(0) @binding(0) var<storage, read> s : S;
 
-let c : u32 = 1u;
+const c : u32 = 1u;
 
 fn f() {
   let b : f32 = s.b[c];
@@ -1409,7 +1461,7 @@ struct S {
 
 @group(0) @binding(0) var<storage, read> s : S;
 
-let c : u32 = 1u;
+const c : u32 = 1u;
 
 fn f() {
   let b : f32 = s.b[min(1u, (arrayLength(&(s.b)) - 1u))];

src/tint/transform/single_entry_point_test.cc

@@ -186,13 +186,13 @@ fn comp_main1() {
 
 TEST_F(SingleEntryPointTest, GlobalConstants) {
     auto* src = R"(
-let a : f32 = 1.0;
+const a : f32 = 1.0;
 
-let b : f32 = 1.0;
+const b : f32 = 1.0;
 
-let c : f32 = 1.0;
+const c : f32 = 1.0;
 
-let d : f32 = 1.0;
+const d : f32 = 1.0;
 
 @vertex
 fn vert_main() -> @builtin(position) vec4<f32> {
@@ -217,7 +217,7 @@ fn comp_main2() {
 )";
 
     auto* expect = R"(
-let c : f32 = 1.0;
+const c : f32 = 1.0;
 
 @compute @workgroup_size(1)
 fn comp_main1() {
@@ -238,6 +238,32 @@ TEST_F(SingleEntryPointTest, WorkgroupSizeLetPreserved) {
     auto* src = R"(
 let size : i32 = 1;
 
+@compute @workgroup_size(size)
+fn main() {
+}
+)";
+
+    auto* expect = R"(
+const size : i32 = 1;
+
+@compute @workgroup_size(size)
+fn main() {
+}
+)";
+
+    SingleEntryPoint::Config cfg("main");
+
+    DataMap data;
+    data.Add<SingleEntryPoint::Config>(cfg);
+    auto got = Run<SingleEntryPoint>(src, data);
+
+    EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(SingleEntryPointTest, WorkgroupSizeConstPreserved) {
+    auto* src = R"(
+const size : i32 = 1;
+
 @compute @workgroup_size(size)
 fn main() {
 }

src/tint/transform/unshadow_test.cc

@@ -402,7 +402,7 @@ fn Z() {
 )";
 
     auto* expect = R"(
-let a : i32 = 1;
+const a : i32 = 1;
 
 fn X() {
   var a_1 = (a == 123);
@@ -452,7 +452,7 @@ fn Z() {
   const a_3 = 321;
 }
 
-let a : i32 = 1;
+const a : i32 = 1;
 )";
 
     auto got = Run<Unshadow>(src);
@@ -473,7 +473,7 @@ fn Y() {
 }
 
 fn Z() {
-  const a = a;
+  const a = 321;
 }
 )";
 
@@ -489,7 +489,7 @@ fn Y() {
 }
 
 fn Z() {
-  const a_3 = a;
+  const a_3 = 321;
 }
 )";
 
@@ -741,7 +741,7 @@ fn F(a : bool) {
 )";
 
     auto* expect = R"(
-let a : i32 = 1;
+const a : i32 = 1;
 
 fn F(a_1 : bool) {
 }
@@ -764,7 +764,7 @@ let a : i32 = 1;
 fn F(a_1 : bool) {
 }
 
-let a : i32 = 1;
+const a : i32 = 1;
 )";
 
     auto got = Run<Unshadow>(src);

src/tint/transform/var_for_dynamic_index_test.cc

@@ -484,7 +484,8 @@ TEST_F(VarForDynamicIndexTest, ArrayIndexConstantLet) {
 fn f() {
   let p = array<i32, 4>(1, 2, 3, 4);
   let c = 1;
-  let x = p[c];
+  var var_for_index = p;
+  let x = var_for_index[c];
 }
 )";
 
@@ -501,7 +502,8 @@ TEST_F(VarForDynamicIndexTest, MatrixIndexConstantLet) {
 fn f() {
   let p = mat2x2(1.0, 2.0, 3.0, 4.0);
   let c = 1;
-  let x = p[c];
+  var var_for_index = p;
+  let x = var_for_index[c];
 }
 )";