feat(semantic): Warn when an extern type/function is declared outside the corelib. by orizi · Pull Request #10147 · starkware-libs/cairo

orizi · 2026-06-22T11:16:35Z

Summary

Introduces a new extern_outside_corelib lint (warning E2201) that fires when extern fn or extern type items are declared outside the core library. The warning message reads: "Extern types and functions should only be declared in the core library." It can be suppressed with #[allow(extern_outside_corelib)].

The lint is registered as a known allow-able lint in declared_allows, and the check is implemented in report_extern_item_outside_corelib, which is called from both extern_function.rs and extern_type.rs during semantic analysis. The constant EXTERN_OUTSIDE_CORELIB is added to cairo-lang-syntax's attribute consts.

All existing test fixtures that declare extern fn or extern type outside the corelib have been updated with #[allow(extern_outside_corelib)] to suppress the new warning, and line numbers in expected diagnostics have been adjusted accordingly. New test cases in diagnostic_test_data/allow verify that the warning is emitted without the attribute and suppressed with it.

Type of change

Please check one:

Bug fix (fixes incorrect behavior)
New feature
Performance improvement
Documentation change with concrete technical impact
Style, wording, formatting, or typo-only change

Why is this change needed?

Declaring extern fn and extern type outside the core library is an advanced, low-level operation that bypasses Cairo's type system guarantees and directly names Sierra libfuncs. Allowing this silently in user code makes it easy to accidentally introduce unsound or non-portable declarations. The lint surfaces this as a warning so developers are aware of the risk, while still allowing it when explicitly opted in.

What was the behavior or documentation before?

extern fn and extern type could be declared anywhere without any diagnostic.

What is the behavior or documentation after?

Declaring extern fn or extern type outside the core library emits warning E2201. The warning is silenced by annotating the item with #[allow(extern_outside_corelib)].

Related issue or discussion (if any)

Additional context

The error code E2201 is assigned to this diagnostic. The severity is Warning, consistent with other lint-style diagnostics such as unused_variables and unused_imports.

reviewable-StarkWare · 2026-06-22T11:16:46Z

This change is

orizi · 2026-06-22T11:16:49Z

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cursor · 2026-06-22T11:19:18Z

PR Summary

Low Risk
Lint-only semantic change with broad test fixture updates; no runtime or corelib behavior change.

Overview
Adds warning E2201 when extern fn or extern type is declared outside the core crate. Semantic analysis calls report_extern_item_outside_corelib from extern function and extern type declaration paths; the core crate and items with #[allow(extern_outside_corelib)] are exempt. The lint name is registered in declared_allows via new constant EXTERN_OUTSIDE_CORELIB.

Compiler test fixtures that intentionally use extern items in tests are annotated with #[allow(extern_outside_corelib)], with expected diagnostic line numbers adjusted where module code grew. New allow-lint tests cover the warning and suppression behavior.

^{Reviewed by Cursor Bugbot for commit 7b1ecc8. Bugbot is set up for automated code reviews on this repo. Configure here.}

TomerStarkware

@TomerStarkware reviewed 78 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on eytan-starkware).

eytan-starkware

@eytan-starkware reviewed 78 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on orizi).

crates/cairo-lang-semantic/src/diagnostic.rs line 808 at r2 (raw file):

            }
            SemanticDiagnosticKind::ExternItemOutsideCorelib => {
                "Extern types and functions should only be declared in the core library.".into()

Maybe guidance: "Extern... expected only in .... To allow use #[....] "

eytan-starkware

@eytan-starkware reviewed 78 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on orizi).

crates/cairo-lang-semantic/src/diagnostic.rs line 808 at r2 (raw file):

            }
            SemanticDiagnosticKind::ExternItemOutsideCorelib => {
                "Extern types and functions should only be declared in the core library.".into()

Maybe guidance: "Extern... expected only in .... To allow use #[....] "

… the corelib. Adds the `extern_outside_corelib` warning (E2201), emitted on any `extern type` or `extern fn` declared outside the core crate. Silenceable per-item with `#[allow(extern_outside_corelib)]`; internal tests that declare externs are annotated accordingly.

orizi

@orizi made 1 comment.
Reviewable status: 76 of 78 files reviewed, 1 unresolved discussion (waiting on eytan-starkware and TomerStarkware).

crates/cairo-lang-semantic/src/diagnostic.rs line 808 at r2 (raw file):

Previously, eytan-starkware wrote…

Maybe guidance: "Extern... expected only in .... To allow use #[....] "

Done.

eytan-starkware

@eytan-starkware reviewed 2 files and all commit messages, made 1 comment, and resolved 1 discussion.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on orizi).

orizi requested review from TomerStarkware and eytan-starkware June 22, 2026 11:16

orizi marked this pull request as ready for review June 22, 2026 11:19

TomerStarkware approved these changes Jun 22, 2026

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orizi added this pull request to the merge queue Jul 3, 2026

github-merge-queue Bot removed this pull request from the merge queue due to failed status checks Jul 3, 2026

orizi force-pushed the orizi/06-22-feat_semantic_warn_when_an_extern_type_function_is_declared_outside_the_corelib branch from f8af227 to 01c3432 Compare July 3, 2026 16:01

eytan-starkware requested changes Jul 5, 2026

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orizi force-pushed the orizi/06-22-feat_semantic_warn_when_an_extern_type_function_is_declared_outside_the_corelib branch from 01c3432 to 7b1ecc8 Compare July 5, 2026 12:23

orizi commented Jul 5, 2026

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eytan-starkware approved these changes Jul 5, 2026

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orizi added this pull request to the merge queue Jul 5, 2026

Merged via the queue into main with commit cb0fcd7 Jul 5, 2026
55 checks passed

orizi deleted the orizi/06-22-feat_semantic_warn_when_an_extern_type_function_is_declared_outside_the_corelib branch July 8, 2026 09:59

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feat(semantic): Warn when an extern type/function is declared outside the corelib. - #10147

feat(semantic): Warn when an extern type/function is declared outside the corelib.#10147
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Summary

Type of change

Why is this change needed?

What was the behavior or documentation before?

What is the behavior or documentation after?

Related issue or discussion (if any)

Additional context

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orizi commented Jun 22, 2026 •

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