fix(auto-import): don't suggest # imports that only resolve via condition fallback

[Marwan (marwan562)]

With imports": { "#*": { "node": "./dist/*/index.js", "default": "./dist/*.js" } } and nodenext, auto-import offered both #utils/summarize and #utils/summarize/summarize. The second only resolves in TS by falling back from node to default after the node target misses. Node picks the first matching condition and throws ERR_MODULE_NOT_FOUND instead, so picking that suggestion crashes at runtime.

Reverse mapping in tryGetModuleNameFromExportsOrImports did the same fallback as the resolver. It now mirrors Node first-match: when a runtime-active condition misses, later conditions aren't tried. types/types@ don't block since Node ignores them, nested objects with no active runtime key still fall through, and array fallback still works.

Added cases alongside the existing ones in tsc/internal/modulespecifiers/specifiers_test.go.

Fixes #64171
Related #62439, #50762

Disclosure: I used AI assistance to draft this patch and reviewed and tested it myself.

[Copilot]

🟡 Changes recommended

Two moderate resolution-semantics issues could still produce incorrect auto-import behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Updates auto-import reverse mapping to better match Node.js conditional import resolution.

Changes:

• Stops fallback after matching runtime conditions.
• Adds conditional, nested, types-only, and array mapping tests.

File summaries

File	Review
tsc/internal/modulespecifiers/specifiers.go	Requires fixes for deeper conditional objects and Node array-target semantics.
tsc/internal/modulespecifiers/specifiers_test.go	Adds regression coverage, but incorrectly expects file-existence fallback for arrays.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Marwan (marwan562)]

@microsoft-github-policy-service agree

[Marwan (marwan562)]

Addressed both Copilot comments:

• Arrays now treat first valid string as terminal (no file-existence fallback). Second-element match test corrected to expect blocked, first-element still valid. Undefined array entries (inactive conditional) still fall through.
• Nested conditionals now track terminal vs undefined via tri-state return, so { node: { import: { browser: ... } }, default } with inactive browser correctly falls back to default.

Added deeper-nesting + array-undefined-first cases. All modulespecifiers tests pass.

Copilot review

[Copilot]

🟡 Changes recommended

The critical and moderate fallback-handling issues must be resolved before approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (2)

tsc/internal/modulespecifiers/specifiers.go:1337

• An exhausted array is not always equivalent to an undefined nested conditional. Node treats an empty array as null (terminal), and throws the last invalid-target error when all entries are invalid; only an array whose entries all resolve to undefined may fall through. Returning blocked=false here makes maps such as { "node": [], "default": "./dist/index.js" } suggest the default even though Node rejects that specifier. Track these outcomes separately and propagate a terminal result for empty/all-invalid arrays.

		return "", false

tsc/internal/modulespecifiers/specifiers_test.go:393

• These cases only invoke the private reverse-mapping helper, but the regression is specifically the LSP auto-import/Quick Fix result. Add a Fourslash regression using the issue's package.json/project layout and assert the exact list with VerifyImportFixModuleSpecifiers; existing package-import auto-import coverage uses that path (for example, tsc/internal/fourslash/tests/autoImportPackageJsonImportsConditions_test.go:10-29). This ensures the invalid suggestion is actually filtered through the full language-server flow.

				result := tryGetModuleNameFromExportsOrImports(

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

[Marwan (marwan562)]

Addressed the two Sep 8 Copilot threads:

• String validity (specifiers.go:1322 + 1337): string misses now check isValidPackageTarget (same rules as forward resolver: ./ prefix, bare-specifier allowance for imports, .././node_modules segments). Invalid targets return statusInvalid (skipped in arrays, terminal in conditionals); valid misses stay terminal. ["invalid", "./dist/index.js"] now falls through to the valid entry.
• Types-only arrays (specifiers.go:1334): threaded inTypesOnly through conditional/array recursion, so "types": ["./missing.d.ts", "./index.d.ts"] preserves TS declaration fallback and never blocks outer default (Node ignores the subtree at runtime).

Also handled suppressed feedback: empty and all-invalid arrays are terminal at runtime (only all-undefined falls through), and added Fourslash regression TestAutoImportPackageJsonImportsInvalidSpecifier using the issue layout with VerifyImportFixModuleSpecifiers.

All modulespecifiers + TestAutoImportPackageJson* Fourslash tests pass.

Copilot review