refactor(inference): add structural type mapping

[ematipico]

Summary

This PR adds some plumbing to substitute generics inside a graph of types. Generics are called "slots".

There's also some plumbing for:

• transformation
• substitutions

Both work using a DFS iterator.

The new implementation:

• Extracts immediate type slots with TypeDataSlots and rebuilds their original parent through TypeDataSlotRebuilder.
• Uses TypeDataSlotReplacements to validate replacement counts and ensure every replacement is consumed.
• Adds an iterative TypeDataTransformer with a shared step limit and protection against recursive types.
• Adds TypeSubstitution, TypeTransformResult, and TypeTransformError.
• Exposes semantic substitution through TypeData::substitute_type and TypeData::substitute_type_in_root_body.
• Preserves generic binder boundaries and generic declaration identity during substitution.
• Updates inference consumers to handle incomplete transformations conservatively.

The generic transformation machinery remains private; callers use the semantic substitution APIs.

Test Plan

Added structural mapping unit tests and passed type-info tests and all-target clippy.

Docs

N/A

This PR was created with AI assistance (OpenCode).

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Latest commit: 52605ce

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[github-actions]

✅ Organic activity

No automation signals detected in the analyzed events.

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[ematipico]

• refactor(inference): remove the legacy type engine #10937
• refactor(inference): prepare legacy type removal #11010
• refactor(analyzer): cut over inferred type consumers #11009
• fix(inference): handle import cycles #11008
• refactor(inference): port Salsa module inference #11006
• refactor(inference): add canonical inferred globals #11005
• refactor(inference): add structural type mapping #11004 👈 (View in Graphite)
• refactor(inference): separate raw type collection #11003
• refactor(lint): extract return type relation #10973
• fix(inference): suppress incomplete type results #10972
• fix(inference): improve member and Promise inference #10971
• fix(inference): improve overload selection #10970
• fix(inference): improve imported and aliased types #10936
• main

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[github-actions]

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 53410220-f4bb-453f-bc5e-8a848228b5db

📥 Commits

Reviewing files that changed from the base of the PR and between 2370747 and 52605ce.

📒 Files selected for processing (2)

• crates/biome_js_type_info/src/interned_types.rs
• crates/biome_js_type_info/src/type_transform.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• crates/biome_js_type_info/src/type_transform.rs
• crates/biome_js_type_info/src/interned_types.rs

---

Walkthrough

The PR adds bounded slot-based TypeData transformation and fallible generic substitution. Generic replacement collection now reports step-limit failures, while module-graph inference propagates failed transformations as Unknown. Tests cover traversal limits, result errors, slot replacement semantics, and reconstruction round trips.

Possibly related PRs

• biomejs/biome#10888 — Refactors the same generic type-substitution machinery.
• biomejs/biome#10936 — Also updates generic substitution and its type-inference call sites.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and matches the main change: adding structural type mapping for inference.
Description check	✅ Passed	The description clearly matches the implemented type-slot substitution and transformation changes.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 12-add-structural-type-mapping

---

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[coderabbitai]

🧹 Nitpick comments (1)

crates/biome_js_type_info/src/interned_types.rs (1)

671-675: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Tidy up the duplicated region markers.

Lines 671–673 open and immediately close an empty // #region Structural construction, and line 675 opens a second region with the same label. Looks like a copy/paste leftover — dropping the empty block keeps the section headers meaningful.

🧹 Suggested tidy-up

-    // `#region` Structural construction
-
-    // `#endregion`
-
     // `#region` Structural construction

As per coding guidelines: "Write comments only when they convey information not recoverable from code".

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/biome_js_type_info/src/interned_types.rs` around lines 671 - 675,
Remove the empty duplicated `// `#region` Structural construction` block in
`interned_types.rs`, keeping only the subsequent meaningful region marker and
its contents.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@crates/biome_js_type_info/src/interned_types.rs`:
- Around line 671-675: Remove the empty duplicated `// `#region` Structural
construction` block in `interned_types.rs`, keeping only the subsequent
meaningful region marker and its contents.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 1b124294-ee72-4f21-9c70-31e3e5a1e783

📥 Commits

Reviewing files that changed from the base of the PR and between de8c2af and b2ab727.

📒 Files selected for processing (7)

• crates/biome_js_type_info/src/interned_types.rs
• crates/biome_js_type_info/src/lib.rs
• crates/biome_js_type_info/src/resolved.rs
• crates/biome_js_type_info/src/type_transform.rs
• crates/biome_module_graph/src/db/queries/type_inference.rs
• crates/biome_module_graph/src/db/type_inference/expressions.rs
• crates/biome_module_graph/src/db/type_inference/lookup.rs

[codspeed-hq]

Merging this PR will degrade performance by 17.24%

❌ 2 (👁 2) regressed benchmarks
✅ 77 untouched benchmarks
⏩ 192 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
👁	bench_normalize_local_alias	33.1 µs	40.2 µs	-17.62%
👁	bench_normalize_terminal_type	21.1 µs	25.4 µs	-16.85%

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_{Comparing 12-add-structural-type-mapping (52605ce) with main (de8c2af)}

Footnotes

1. 192 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩