TypeScript parser rejects generic call signatures, export type * and variance annotations #97

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1. DaisukeYoda commented on Sep 17, 2026

   

   DaisukeYoda

   on Sep 17, 2026

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   Another construct in this same class, found by the FP-audit skill on rogerpadilla/uql@6252e1f: abstract override on a property declaration (TS 4.3+).

   abstract class Base { abstract p: string; }
   export abstract class C extends Base { abstract override p: string; }

   [e.ts] parse_error: syntax error at line 2
   

   The modifiers are only rejected in combination, and only on a property:

   construct	parses
   abstract readonly p: string	yes
   override readonly p: string	yes
   abstract override m(): void (method)	yes
   abstract override p: string (property)	no

   In uql this hits two files, dialect/abstractSqlDialect.ts:234 and dialect/vectorSqlDialect.ts:26.

   Score impact

   Worth recording here because this issue notes that skipped files are removed from every score but does not quantify it. Replacing abstract override readonly with abstract readonly in those two files, changing nothing else:

   	skipped	analyzed	functions	LOC	health	grade
   as-is	2	280	3635	44584	57	D
   one-token patch	0	282	3831	47282	69	C

   Two unparsable files out of 282 cost 12 health points and a full letter grade, and hide 196 functions and 2698 LOC. The parse-error penalty and the excluded content compound, so the blast radius of each construct listed in this issue is larger than the file count suggests.

   polyscan 0.4.0 (be31afc).
2. DaisukeYoda commented on Sep 17, 2026

   

   DaisukeYoda

   on Sep 17, 2026

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   Follow-up on the first bullet, which I think is mis-stated, plus a grammar-level probe that tells you what one fix would cover.

   The generic call signature case needs two of them, not one

   A single generic call signature parses fine. The trigger is two or more consecutive generic call signatures in the same interface or type literal, which is to say a generic overload set.

   interface G {
     <T>(x: T): T   // alone: parses
     <U>(x: U): U   // second one: syntax error on this line
   }

   shape	parses
   one generic call signature	yes
   generic call signature followed by a non-generic one	yes
   two consecutive generic call signatures	no
   three consecutive	no

   That matches the files listed in the issue. src/context.ts:96 is the first of two generic call signatures in interface Get<E extends Env>, and the second is on line 97. src/utils/body.ts:94 is the closing line of the first of two generic call signatures in interface ParseBody. Reproduced on hono at HEAD, 8 of its src files skipped, same line numbers as the issue reports.

   The distinction matters because "generic call signatures are rejected" sends a reader looking at the wrong construct. The type parameters are not the problem. Two of them in a row are.

   All of these fail inside tree-sitter, in both grammars

   I probed the vendored grammar directly, parsing each construct with smacker/go-tree-sitter and reading HasError() on the root node, before any polyscan code runs:

   construct	typescript grammar	tsx grammar
   two consecutive generic call signatures	error	error
   variance annotation (TS 4.7)	error	error
   export type * from (TS 5.0)	error	error
   abstract override on a property (TS 4.3), from my earlier comment	error	error
   plain class, control	ok	ok

   Two things follow. First, none of these are polyscan-side handling, so a single grammar bump should clear all four constructs at once. The pin is github.com/smacker/go-tree-sitter v0.0.0-20240827094217-dd81d9e9be82, from August 2024. Second, the typescript and tsx grammars behave identically here, so the choice of tsx for .ts files at polyscan/internal/js/parser/parser.go:35 is not a contributing factor. I checked that specifically because it looked like a plausible cause and it is not one.
3. DaisukeYoda commented on Sep 21, 2026

   

   DaisukeYoda

   on Sep 21, 2026

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   Another construct in this class, found by the FP-audit skill on almeidazs/better-drizzle@23527ae: an import type carrying a type-operator suffix, meaning import('./m').Foo<T>, import('./m').Foo[] or import('./m').Foo['k'].

   The import type itself parses. It only fails once a suffix is applied to it:

   construct	parses
   import('./m').Foo	yes
   import('./m').NS.Foo	yes
   import('./m').Foo | string, & {a:1}	yes
   typeof import('./m').foo	yes
   import('./m').Foo<string>	no
   import('./m').Foo[]	no
   import('./m').Foo['k']	no
   import('./m').NS.Foo<string>	no
   Foo<string> / Foo[] on an ordinary imported type	yes

   The same suffixes on an ordinary type reference are fine, so the suffix grammar works in general and only the import-type operand is missing it.

   One position is exempt. In an as cast the suffixed form parses, which is why a file can use the construct and still be analyzed:

   const y = x as unknown as import('./m').Foo<string>;  // parses
   type A = import('./m').Foo<string>;                   // syntax error

   In better-drizzle this accounts for 6 of the 7 skipped files (src/types/{delegate,hooks,query,runtime,transaction}.ts, src/plugins/zod/index.ts), and export type * from accounts for the seventh.

   Confirmed in the grammar, both variants

   Same probe method as my earlier comment, reading HasError() on the root node before any polyscan code runs:

   construct	typescript	tsx
   import('./m').Foo<string>	error	error
   import('./m').Foo[]	error	error
   import('./m').Foo['k']	error	error
   plain class, control	ok	ok

   So this is the same situation as the four constructs already listed. It sits in the vendored grammar rather than in polyscan, and a single bump of the smacker/go-tree-sitter pin should clear it along with the rest.

   Score impact

   Patching only the three failing constructs in those 7 files, changing nothing else:

   	skipped	analyzed	functions	LOC	health	grade
   as-is	7	87	789	23311	73	C
   patched	0	94	801	28006	82	B

   Nine health points and a full letter grade. The 4695 hidden LOC are 17 percent of the real total, so a reader of the as-is report is judging about five sixths of the tree.

   The penalty arithmetic reconciles exactly in both runs: raw dimension penalties sum to 15.40 against a 96 point budget, giving 84 before the parse penalty, and the reported 73 implies a parse penalty of exactly 11, which is the MinParseErrorPenalty floor. The patched run lands on 82 with a parse penalty of 0.

   Skipped files distort other analyses, in both directions

   This is the part I had not expected, and it argues the blast radius is wider than the health score.

   A skipped file's import edges vanish, so symbols it consumes look dead. src/plugins/rules/index.ts is skipped for export type *, and it re-exports four functions from ./shared/presets. All four are reported as dead code, together with a fifth export the same barrel consumes:

   unused_exported_function  src/plugins/rules/shared/presets.ts:3    'mergeRules'
   unused_exported_function  src/plugins/rules/shared/presets.ts:14   'safe'
   unused_exported_function  src/plugins/rules/shared/presets.ts:60   'recommended'
   unused_exported_function  src/plugins/rules/shared/presets.ts:152  'strict'
   unused_export             src/plugins/rules/shared/plugin.ts:1242  'default'
   

   All five disappear once the barrel parses. They are false positives manufactured by the parse failure, in files that parsed perfectly well themselves, which means a parse error is not contained to the file that caused it.

   In the other direction, the dependency score moves from 85 to 75 once the files parse. The excluded files were hiding real dependency debt, so that dimension read healthier than the truth while the flat 11 point penalty made the total read worse. Parse errors are not a uniform downward bias on the report, and a reader cannot correct for them by assuming the real grade is somewhat better.

   polyscan 0.4.1 (e767a21).
4. DaisukeYoda commented on Oct 15, 2026

   

   DaisukeYoda

   on Oct 15, 2026

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   A grammar bump does not fix this. smacker/go-tree-sitter is already pinned at its latest commit (dd81d9e, 2024-08-27), and the repository has had no commits since then.

   I probed the official bindings (github.com/tree-sitter/go-tree-sitter v0.25.0) with tree-sitter-typescript v0.23.2, the latest release, and with its master branch (75b3874, 2025-01-30). All five constructs in this issue still produce HasError() in both the typescript and tsx grammars:

   construct	v0.23.2	master
   two consecutive generic call signatures	error	error
   export type * from	error	error
   variance annotations (in/out)	error	error
   abstract override on a property	error	error
   import type with a <T>, [] or ['k'] suffix	error	error
   controls: satisfies, accessor, export type { A }, a generic interface	ok	ok

   A fix therefore needs grammar changes: a patched fork of tree-sitter-typescript with a regenerated parser.c. Switching to the official Go bindings alone does not help.