Interop gen additional literal types by sagar-h007 · Pull Request #503 · dart-lang/web

sagar-h007 · 2026-01-11T14:53:56Z

This PR improves interop_gen support for TypeScript literal types that aren’t represented as simple literals in the AST (for example, prefix unary expressions like -1).

When a literal can’t be handled directly, the generator now falls back to the TypeScript TypeChecker to resolve the type. If the resolved type is a literal, its value is used; otherwise, the code safely falls back to the underlying Dart type, preserving existing behavior.

The change also adds the minimal TypeScript bindings needed for this resolution and includes an integration test to cover the new case and prevent regressions.

Fixes:#465

I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

•	This is a small, targeted change based on an existing issue.
•	The code follows the Dart style guide and is formatted with dart format.
•	New integration tests were added, and all existing tests pass locally.
•	No changelog or pubspec update is needed for this internal tooling change.

gemini-code-assist · 2026-01-11T14:54:11Z

Summary of Changes

Hello @sagar-h007, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the interop_gen tool's capability to accurately process and generate Dart interop code for a wider range of TypeScript literal types. By integrating the TypeScript TypeChecker for more advanced type resolution, the tool can now correctly interpret literals that are not simple AST nodes, ensuring greater fidelity and compatibility between TypeScript definitions and generated Dart code.

Highlights

Enhanced TypeScript Literal Type Handling: The interop_gen tool now better supports complex TypeScript literal types, such as prefix unary expressions like -1, which were not directly represented as simple literals in the AST.
TypeScript TypeChecker Fallback: When a literal type cannot be handled directly from the AST, the generator now falls back to using the TypeScript TypeChecker to resolve the type, providing more robust type inference.
Graceful Type Resolution: If the TypeChecker resolves to a literal type, its value is used. Otherwise, the system safely falls back to the underlying Dart type, preserving existing behavior and preventing errors for unresolvable literals.
New TypeScript Bindings and Integration Test: Minimal TypeScript bindings required for the TypeChecker resolution have been added, along with a new integration test to cover these new cases and prevent future regressions.

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Code Review

This pull request enhances interop_gen to support more complex TypeScript literal types by leveraging the TypeScript TypeChecker, which is a solid improvement. The changes are well-structured and include relevant integration tests. I've identified one critical issue in the new TypeScript bindings that would lead to a compilation error due to an incorrect type definition. Additionally, I have a couple of medium-severity suggestions for the transformer logic to improve code clarity and efficiency by reducing redundancy. Once the critical issue is resolved, this will be a great addition.

nikeokoronkwo · 2026-01-12T03:39:37Z

I don't think there are much examples, or additions of code for other literal types, as needed for #465.

You mentioned in one of the files that binary expressions are not allowed in TypeScript Declaration files: the reason for the issue is because these types were present in NPM packages I was testing with.

sagar-h007 · 2026-01-12T06:08:07Z

@nikeokoronkwo I agree that these cases aren’t common in well-formed .d.ts files. The main goal here was to better handle real-world declarations coming from generated or loosely authored NPM typings, while still relying on the TypeScript TypeChecker and falling back safely where needed.

The change is intentionally conservative and shouldn’t affect valid declaration files.

srujzs

Thanks! If we feel like this doesn't fully resolve #465, we can keep that bug open and just update it with has been resolved.

srujzs · 2026-01-13T22:41:44Z

@@ -0,0 +1,8 @@
+export declare const negativeOne: -1;
+// Binary expressions in type position are not valid TS in d.ts files usually.


Do we have an example we can test where it is valid?

I looked into this but couldn’t find a realistic case where binary expressions are valid in .d.ts files. In practice, numeric literals like -1 seem to be the only form that’s commonly supported.
To avoid adding a test that isn’t representative or might be TS-version dependent, I limited coverage to those cases and added a note explaining the limitation.

srujzs · 2026-01-13T22:51:37Z

+              }
+
+              // Fallback to underlying type if not a literal
+              final underlyingTypeNode = typeChecker.typeToTypeNode(


Is there a test exercising this case?

Not yet ,. I’ll add a test to explicitly exercise this fallback path.

I might have missed it, but which test case covers this?

Use a shared helper to reduce duplication, remove unused TSTypeFlags, and add integration tests for false, null, and negative numeric literals.

srujzs

Mostly LGTM % my comments.

srujzs · 2026-01-14T16:57:47Z

 // export declare const shiftLeft: 1 << 16;
 // export declare const complex: 1 + 2 * 3;
-export declare const existingLiteral: 1;
+// export declare const existingLiteral: 1;


Did you mean to comment this test out?

Yes, intentionally commented out to avoid duplicating coverage. Happy to re-enable if you think it improves clarity.

Yeah, let's re-enable to add some coverage for non-negative numbers. Probably doesn't make a difference in the code but the original bug highlighted prefix unary expressions, so having that as a separate test case makes sense.

Refactor literal handling to use scoped, typed helpers instead of a generic value-based helper. Clean up unused TSTypeFlags and add integration tests for false, null, and resolved-type literals.

srujzs · 2026-01-14T19:18:09Z

 // export declare const shiftLeft: 1 << 16;
 // export declare const complex: 1 + 2 * 3;
-export declare const existingLiteral: 1;
+// export declare const existingLiteral: 1;


Yeah, let's re-enable to add some coverage for non-negative numbers. Probably doesn't make a difference in the code but the original bug highlighted prefix unary expressions, so having that as a separate test case makes sense.

srujzs · 2026-01-14T19:19:39Z

+              }
+
+              // Fallback to underlying type if not a literal
+              final underlyingTypeNode = typeChecker.typeToTypeNode(


I might have missed it, but which test case covers this?

sagar-h007 · 2026-01-14T20:18:56Z

It’s covered by the negativeOne (-1) case in
test/integration/interop_gen/literal_test_input.d.ts, which exercises the prefix unary expression path this fallback is meant to handle.

srujzs · 2026-01-15T22:39:51Z

Ack, I think the only thing left is the uncomment (and generate the expectation file) and we can go ahead and land this.

sagar-h007 · 2026-01-16T17:54:37Z

@srujzs Done — re-enabled the test using a 1n BigInt to hit the fallback path and updated the expected output. All tests are passing.

auto-submit · 2026-01-16T20:58:27Z

autosubmit label was removed for dart-lang/web/503, because This PR has not met approval requirements for merging. The PR author is not a member of dart-team and needs 1 more review(s) in order to merge this PR.

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Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com> commit 5edd2dd Author: Kevin Moore <kevmoo@users.noreply.github.com> Date: Tue Feb 3 17:18:04 2026 -0800 Fix use_null_aware_elements lint (dart-lang#518) commit d1958f8 Author: Sagar <halladakerisagar@gmail.com> Date: Wed Feb 4 06:29:06 2026 +0530 Support TypeScript indexed access types in interop_gen (dart-lang#509) * Support TypeScript indexed access types in interop_gen * Fix:prevent IndexedAccessType fallback from generating unsupported bindings * Remove unused indexed access fallback flag and simplify resolution logic * fixed analyzer issue * fix format issue * Improve IndexedAccessType handling and add composed type tests * interop_gen: refactor indexed access resolution, remove dead code, and Add test for symbol indexed access with primitive return type commit 2590763 Author: Harshita Yadav <seemayadavanuj123@gmail.com> Date: Mon Jan 26 23:40:27 2026 +0530 docs: clarify document.cookie nullability when migrating from dart:html (dart-lang#510) * docs: clarify document.cookie nullability when migrating from dart:html * docs: organize migration notes under specific APIs commit b9b1b38 Author: Sagar <halladakerisagar@gmail.com> Date: Sat Jan 17 02:31:52 2026 +0530 Interop gen additional literal types (dart-lang#503) * interop_gen: support additional literal type expressions via TypeChecker * fixed analyzer warning * simplify literal parsing and improve readability * Refactor literal handling and expand literal tests Use a shared helper to reduce duplication, remove unused TSTypeFlags, and add integration tests for false, null, and negative numeric literals. * Use typed literal helpers in _transformType and add tests Refactor literal handling to use scoped, typed helpers instead of a generic value-based helper. Clean up unused TSTypeFlags and add integration tests for false, null, and resolved-type literals. * fix CI issue * enable fallback literal coverage and update expectations commit 1dfcee7 Author: Harshita Yadav <seemayadavanuj123@gmail.com> Date: Fri Jan 16 03:21:37 2026 +0530 docs(web_generator): document minimum supported Node.js version (dart-lang#508) * docs(web_generator): document minimum supported Node.js version * docs(web_generator): simplify Node.js version wording

sagar-h007 added 2 commits January 11, 2026 19:48

interop_gen: support additional literal type expressions via TypeChecker

e8c4d2f

fixed analyzer warning

fdaf0cf

gemini-code-assist Bot reviewed Jan 11, 2026

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Comment thread web_generator/lib/src/js/typescript.types.dart

Comment thread web_generator/lib/src/interop_gen/transform/transformer.dart Outdated

Comment thread web_generator/lib/src/interop_gen/transform/transformer.dart Outdated

simplify literal parsing and improve readability

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nikeokoronkwo linked an issue Jan 12, 2026 that may be closed by this pull request

Interop Gen: Support Complex Literal Type Expressions #465

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srujzs reviewed Jan 13, 2026

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Refactor literal handling and expand literal tests

96d785c

Use a shared helper to reduce duplication, remove unused TSTypeFlags, and add integration tests for false, null, and negative numeric literals.

sagar-h007 requested a review from srujzs January 14, 2026 15:38

srujzs reviewed Jan 14, 2026

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sagar-h007 added 2 commits January 14, 2026 23:37

Use typed literal helpers in _transformType and add tests

03bc013

Refactor literal handling to use scoped, typed helpers instead of a generic value-based helper. Clean up unused TSTypeFlags and add integration tests for false, null, and resolved-type literals.

fix CI issue

535c93d

sagar-h007 requested a review from srujzs January 14, 2026 18:12

srujzs approved these changes Jan 14, 2026

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enable fallback literal coverage and update expectations

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srujzs approved these changes Jan 16, 2026

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srujzs added the autosubmit label Jan 16, 2026

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srujzs merged commit b9b1b38 into dart-lang:main Jan 16, 2026
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nikeokoronkwo mentioned this pull request Jan 17, 2026

Interop Gen: Support Complex Literal Type Expressions #465

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nikeokoronkwo removed a link to an issue Jan 17, 2026

Interop Gen: Support Complex Literal Type Expressions #465

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		@@ -0,0 +1,8 @@
		export declare const negativeOne: -1;
		// Binary expressions in type position are not valid TS in d.ts files usually.

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