Generated, compiled `Codec.typeUrl` is just TS type `string`

[michaelfig]

Situation

Here's a difference from what Telescope generates today versus what I want from it:

diff --git a/src/codegen/circle/cctp/v1/attester.ts b/src/codegen/circle/cctp/v1/attester.ts
index 24d3c1b1dd..c5e728ae6a 100644
--- a/src/codegen/circle/cctp/v1/attester.ts
+++ b/src/codegen/circle/cctp/v1/attester.ts
@@ -26,7 +26,7 @@ function createBaseAttester(): Attester {
   };
 }
 export const Attester = {
-  typeUrl: '/circle.cctp.v1.Attester',
+  typeUrl: '/circle.cctp.v1.Attester' as const,
   encode(
     message: Attester,
     writer: BinaryWriter = BinaryWriter.create(),

Without the as const, the Typescript compiler output is (today vs. what I want):

--- a/dist/codegen/circle/cctp/v1/attester.d.ts.orig      2025-07-11 20:52:11
+++ b/dist/codegen/circle/cctp/v1/attester.d.ts   2025-07-11 18:56:39
@@ -19,7 +19,7 @@
     attester: string;
 }
 export declare const Attester: {
-    typeUrl: string;
+    typeUrl: "/circle.cctp.v1.Attester";
     encode(message: Attester, writer?: BinaryWriter): BinaryWriter;
     decode(input: BinaryReader | Uint8Array, length?: number): Attester;
     fromJSON(object: any): Attester;

Impact

Because of that missing as const, an importer of the compiled files cannot use the narrow typeUrl constants because they're all just string. That's bad because it forces the user to rely on creating type registries rather than just grabbing Codec['typeUrl'].

Solution

Turns out this is really easy to solve:

--- a/packages/ast/src/encoding/proto/props/index.ts
+++ b/packages/ast/src/encoding/proto/props/index.ts
@@ -3,6 +3,9 @@ import { ProtoParseContext } from '../../context';
 import { ProtoType } from '@cosmology/types';
 import { getAminoTypeName, getTypeUrl } from '../../amino';
 
+const asConst = (expr: t.Expression) =>
+  t.tSAsExpression(expr, t.tsTypeReference(t.identifier('const')));
+
 export const createTypeUrlProperty = (
     context: ProtoParseContext,
     proto: ProtoType
@@ -11,7 +14,7 @@ export const createTypeUrlProperty = (
     if (!typeUrl) return;
     return t.objectProperty(
         t.identifier('typeUrl'),
-        t.stringLiteral(typeUrl)
+        asConst(t.stringLiteral(typeUrl))
     )
 };
 
@@ -23,6 +26,6 @@ export const createAminoTypeProperty = (
     if (!str || str.startsWith('/')) return;
     return t.objectProperty(
         t.identifier('aminoType'),
-        t.stringLiteral(str)
+        asConst(t.stringLiteral(str))
     )
 };

With this patch, I don't need anything else from you, but I thought I'd share it in case you wanted to adopt it upstream (with tests, of course).

[michaelfig]

I showed this to @turadg and @mhofman and they thought it was a good idea to merge upstream. @pyramation, what do you think?