feat: add ReturnType parser #2317

rockerBOO · 2025-07-21T22:45:29Z

Handles

ReturnType<typeof functionName>
ReturnType<SomeType['method']>

This was to support more complex types from Redux toolkit store.

This was written mostly by AI which I guided along to get it to know how to get the return type. So some issues might be in how it is being parsed. I can look through the feedback to improve it.

Context:

https://github.com/microsoft/TypeScript/blob/f14b5c8a2f0be503ac455054a91573c63f0e5088/src/services/services.ts#L974-L976

https://github.com/microsoft/TypeScript/blob/f14b5c8a2f0be503ac455054a91573c63f0e5088/src/services/codefixes/fixAwaitInSyncFunction.ts#L56-L67

Possibly related issues:

#1155
#1847
#1887
#1910

domoritz

Thank you. Looks good overall but the code feels more complex than it ought to be.

domoritz · 2025-07-22T06:25:29Z

src/NodeParser/ReturnTypeNodeParser.ts

+            } else {
+                // Case: ReturnType<SomeType["methodName"]> or other complex types
+                // Get the type directly from TypeScript's type system
+                const argType = this.checker.getTypeAtLocation(typeArg);


I really want to a lid the type checker if possible. What cases fail when we remove this branch?

When removing the else branch completely:

test/valid-data/type-return-type-complex/main.ts(15,28): error TSJ - 100: Unknown node of kind "TypeReference" Error: Unknown node of kind "TypeReference" at ReturnTypeNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/NodeParser/ReturnTypeNodeParser.ts:98:19) at ChainNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/ChainNodeParser.ts:37:49) at TypeAliasNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/NodeParser/TypeAliasNodeParser.ts:40:43) at AnnotatedNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/NodeParser/AnnotatedNodeParser.ts:34:47) at ExposeNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/ExposeNodeParser.ts:23:45) at CircularReferenceNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/CircularReferenceNodeParser.ts:24:43) at ChainNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/ChainNodeParser.ts:37:49) at TopRefNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/TopRefNodeParser.ts:14:47) at <anonymous> (/home/rockerboo/code/others/ts-json-schema-generator/src/SchemaGenerator.ts:31:39) at Array.map (<anonymous>)

Yeah, but what line of the example causes this?

test/valid-data/type-return-type-complex/main.ts(15,28)

https://github.com/vega/ts-json-schema-generator/pull/2317/files#diff-410929871b91b13bf666ba5f7b9b865ef50c52318faaa956ef8e99a6cc996c5aR15

Specifically the node ReturnType

If you give me some more context of what to look at, I can take a deeper look to finding a better solution.

domoritz · 2025-07-22T06:25:54Z

src/NodeParser/ReturnTypeNodeParser.ts

+
+            throw new UnknownNodeError(node);
+        } catch (error) {
+            throw error;


This seems like a noop?

Removed the try/catch

domoritz · 2025-07-22T06:27:06Z

src/NodeParser/ReturnTypeNodeParser.ts

+                }
+
+                // Fallback to type checking method
+                const type = this.checker.getTypeOfSymbolAtLocation(symbol, typeArg);


Same as below. In what cases do we need the fallback? Why can't we use the function parser instead of implementing a lot of custom logic here?

Removing this fallback causes issues with implicit function return types. I added a test for this case.

Error: /home/rockerboo/code/others/ts-json-schema-generator/test-no-explicit-return.ts(5,34): error TSJ - 100: Unknown node of kind "TypeReference" Error: Unknown node of kind "TypeReference" at ReturnTypeNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/NodeParser/ReturnTypeNodeParser.ts:110:15) at ChainNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/ChainNodeParser.ts:37:49) at TypeAliasNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/NodeParser/TypeAliasNodeParser.ts:40:43) at AnnotatedNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/NodeParser/AnnotatedNodeParser.ts:34:47) at ExposeNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/ExposeNodeParser.ts:23:45) at CircularReferenceNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/CircularReferenceNodeParser.ts:24:43) at ChainNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/ChainNodeParser.ts:37:49) at TopRefNodeParser.createType (/home/rockerboo/code/others/ts-json-schema-generator/src/TopRefNodeParser.ts:14:47) at <anonymous> (/home/rockerboo/code/others/ts-json-schema-generator/src/SchemaGenerator.ts:31:39) at Array.map (<anonymous>)

Can we reuse some of the existing function parsing logic here?

I tried to poke at it in terms of utilizing the FunctionNodeParser but since it's like an abstraction on top of functions I couldn't find a simple way of doing that. I am not fully aware of how this all works, so I do not know how to make it work well enough like this. Also we have it separated as "functions" but this is more of a data structure format (object, number, boolean, string) because of the ReturnType unless it returns a function (which might need to be further tested).

I can try to make it better but I am just not sure how to connect them.

I added more tests for the different function types though, and also tested methods.

… signature extraction

rockerBOO · 2025-07-23T00:02:40Z

I went a little further into return type of functions returning functions, but got more into a gray area and make this PR more complex. But it wasn't too bad to implement.

const x = () => () => 1;

type X = ReturnType<typeof x>;

Generics with return type of functions returning functions or methods returning functions was a a bit more complex.

const x = <T extends string>() => <T>(): T => "hello";

type X = ReturnType<typeof x>;

domoritz

@arthurfiorette could you help review this?

domoritz · 2025-07-24T09:00:54Z

src/NodeParser/ReturnTypeNodeParser.ts

+        try {
+            const typeName = ts.isIdentifier(node.typeName) ? node.typeName.text : node.typeName.getText();
+            return typeName === "ReturnType" && node.typeArguments?.length === 1;
+        } catch {


Do we need a try catch?

Removed the try/catch.

domoritz · 2025-07-24T09:01:08Z

src/NodeParser/ReturnTypeNodeParser.ts

+            return false;
+        }
+
+        // Check if it's a ReturnType reference


Let's remove unnecessary comments that just explain what happens

rockerBOO added 2 commits July 21, 2025 18:33

feat: add initial ReturnType parser

1bc0449

feat: add ReturnType<SomeType['method']> support

f379eac

domoritz reviewed Jul 22, 2025

View reviewed changes

rockerBOO added 3 commits July 22, 2025 13:33

fix: add implicit return type test

af0482e

feat: add more complex function/method parsing tests. abstract common…

1008735

… signature extraction

chore: formatting

7c06489

domoritz approved these changes Jul 24, 2025

View reviewed changes

rockerBOO added 2 commits July 24, 2025 12:54

fix: removed extra try/catch

e188df5

fix: remove ObjectType

a266867

feat: add ReturnType parser #2317

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feat: add ReturnType parser #2317

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rockerBOO commented Jul 21, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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rockerBOO Jul 22, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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rockerBOO commented Jul 23, 2025

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rockerBOO commented Jul 21, 2025 •

edited

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rockerBOO Jul 22, 2025 •

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