tint/ast: Tighten AST definition of runtime-sized array

Just checking whether the count is nullptr is not sufficient to know
whether the array is fixed-size:

`array` represents a infered type, infered fixed-size array
`array<T>` represents an explicit type, runtime-sized array
`array<T, N>` represents an explicit type, explicit fixed-size array

Bug: tint:1628
Change-Id: I03f547078c015d1d2a8a38308bb5e41c733715ec
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/97589
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>

src/tint/ast/array.cc

@@ -56,11 +56,14 @@ std::string Array::FriendlyName(const SymbolTable& symbols) const {
             out << "@stride(" << stride->stride << ") ";
         }
     }
-    out << "array<" << type->FriendlyName(symbols);
-    if (!IsRuntimeArray()) {
+    out << "array";
+    if (type) {
+        out << "<" << type->FriendlyName(symbols);
+        if (count) {
             out << ", " << SizeExprToString(count, symbols);
         }
         out << ">";
+    }
     return out.str();
 }
 

src/tint/ast/array.h

@@ -35,9 +35,9 @@ class Array final : public Castable<Array, Type> {
     /// @param nid the unique node identifier
     /// @param src the source of this node
     /// @param subtype the type of the array elements
-    /// @param count the number of elements in the array. nullptr represents a
-    /// runtime-sized array.
+    /// @param count the number of elements in the array
     /// @param attributes the array attributes
+    /// @note a runtime-sized array is represented by a null count and a non-null type
     Array(ProgramID pid,
           NodeID nid,
           const Source& src,
@@ -50,7 +50,7 @@ class Array final : public Castable<Array, Type> {
 
     /// @returns true if this is a runtime array.
     /// i.e. the size is determined at runtime
-    bool IsRuntimeArray() const { return count == nullptr; }
+    bool IsRuntimeArray() const { return type != nullptr && count == nullptr; }
 
     /// @param symbols the program's symbol table
     /// @returns the name for this type that closely resembles how it would be

src/tint/ast/array_test.cc

@@ -42,6 +42,14 @@ TEST_F(AstArrayTest, CreateRuntimeArray) {
     EXPECT_TRUE(arr->IsRuntimeArray());
 }
 
+TEST_F(AstArrayTest, CreateInferredTypeArray) {
+    auto* arr = create<Array>(nullptr, nullptr, AttributeList{});
+    EXPECT_EQ(arr->type, nullptr);
+    EXPECT_EQ(arr->count, nullptr);
+    EXPECT_TRUE(arr->Is<Array>());
+    EXPECT_FALSE(arr->IsRuntimeArray());
+}
+
 TEST_F(AstArrayTest, FriendlyName_RuntimeSized) {
     auto* i32 = create<I32>();
     auto* arr = create<Array>(i32, nullptr, AttributeList{});
@@ -66,5 +74,15 @@ TEST_F(AstArrayTest, FriendlyName_WithStride) {
     EXPECT_EQ(arr->FriendlyName(Symbols()), "@stride(32) array<i32, 5>");
 }
 
+TEST_F(AstArrayTest, FriendlyName_InferredTypeAndCount) {
+    auto* arr = create<Array>(nullptr, nullptr, AttributeList{});
+    EXPECT_EQ(arr->FriendlyName(Symbols()), "array");
+}
+
+TEST_F(AstArrayTest, FriendlyName_InferredTypeAndCount_WithStrize) {
+    auto* arr = create<Array>(nullptr, nullptr, AttributeList{create<StrideAttribute>(32u)});
+    EXPECT_EQ(arr->FriendlyName(Symbols()), "@stride(32) array");
+}
+
 }  // namespace
 }  // namespace tint::ast