Fix: Using a scalar constructor defined in a parent scalar doesn't re…

…ference the right scalar (#3573)

```
const a = unixTimestamp.fromISO("...");
```

a would have the scalar utcDateTime not unixTimestamp

.chronus/changes/fix-scalar-constructor-clone-2024-5-12-20-39-42.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: internal
+packages:
+  - "@typespec/compiler"
+---
+
+Fix: Using a scalar constructor defined in a parent scalar doesn't reference the right scalar

packages/compiler/src/core/checker.ts

@@ -5621,7 +5621,6 @@ export function createChecker(program: Program): Checker {
       decorators,
       derivedScalars: [],
     });
-    checkScalarConstructors(type, node, type.constructors, mapper);
     linkType(links, type, mapper);
 
     if (node.extends) {
@@ -5631,6 +5630,7 @@ export function createChecker(program: Program): Checker {
         type.baseScalar.derivedScalars.push(type);
       }
     }
+    checkScalarConstructors(type, node, type.constructors, mapper);
     decorators.push(...checkDecorators(type, node, mapper));
 
     if (mapper === undefined) {
@@ -5695,6 +5695,19 @@ export function createChecker(program: Program): Checker {
     constructors: Map<string, ScalarConstructor>,
     mapper: TypeMapper | undefined
   ) {
+    if (parentScalar.baseScalar) {
+      for (const member of parentScalar.baseScalar.constructors.values()) {
+        const newConstructor: ScalarConstructor = cloneTypeForSymbol(
+          getMemberSymbol(node.symbol, member.name)!,
+          {
+            ...member,
+            scalar: parentScalar,
+          }
+        );
+        linkIndirectMember(node, newConstructor, mapper);
+        constructors.set(member.name, newConstructor);
+      }
+    }
     for (const member of node.members) {
       const constructor = checkScalarConstructor(member, mapper, parentScalar);
       if (constructors.has(constructor.name as string)) {

packages/compiler/src/core/types.ts

@@ -1127,7 +1127,8 @@ export type MemberContainerNode =
   | ModelExpressionNode
   | InterfaceStatementNode
   | EnumStatementNode
-  | UnionStatementNode;
+  | UnionStatementNode
+  | ScalarStatementNode;
 
 export type MemberNode =
   | ModelPropertyNode
@@ -1141,7 +1142,7 @@ export type MemberContainerType = Model | Enum | Interface | Union | Scalar;
 /**
  * Type that can be used as members of a container type.
  */
-export type MemberType = ModelProperty | EnumMember | Operation | UnionVariant;
+export type MemberType = ModelProperty | EnumMember | Operation | UnionVariant | ScalarConstructor;
 
 export type Comment = LineComment | BlockComment;
 

packages/compiler/test/checker/values/scalar-values.test.ts

@@ -49,6 +49,21 @@ describe("instantiate with named constructor", () => {
     ]);
   });
 
+  it("instantiate using constructor from parent scalar", async () => {
+    const value = await compileValue(
+      `b.fromString("a")`,
+      `
+      scalar a { init fromString(val: string);}
+      scalar b extends a { }
+    `
+    );
+    strictEqual(value.valueKind, "ScalarValue");
+    strictEqual(value.type.kind, "Scalar");
+    strictEqual(value.type.name, "b");
+    strictEqual(value.scalar?.name, "b");
+    strictEqual(value.value.name, "fromString");
+  });
+
   it("instantiate from another scalar", async () => {
     const value = await compileValue(
       `b.fromA(a.fromString("a"))`,