Fix #7931: Resolve opened namespaces for attributes in recursive scopes

[Copilot]

Description

Fixes nested module attributes not being resolved in namespace rec / module rec scopes. Previously, using [<Extension>] on a module inside namespace rec would fail with FS0039: The type 'Extension' is not defined, even when open System.Runtime.CompilerServices was in scope.

Root Cause

In recursive scopes, open declarations are processed in Phase1AB — after Phase1A builds module/type entities. But module attributes are checked during Phase1A using envInitial, which doesn't yet include the opened namespaces. In non-recursive scopes, opens are processed sequentially before module attributes are checked, so this issue doesn't occur.

Changes Made

• src/Compiler/Checking/CheckDeclarations.fs: Added preProcessOpensForPhase1A helper that silently resolves open declarations before Phase1A attribute checking. Uses suppressErrorReporting and TemporarilySuspendReportingTypecheckResultsToSink to avoid duplicate diagnostics (since opens are re-processed properly in Phase1AB). Applied at two levels:
  1. Top-level opens in TcMutRecDefns_Phase1 (fixes namespace rec case)
  2. Inner opens in TcTyconDefnCore_Phase1A_BuildInitialModule (fixes nested module case)
• Regression tests: Added 8 test cases in AttributeResolutionInRecursiveScopes.fs covering the issue scenarios (Extension attribute on modules/types in namespace rec, nested modules, multiple opens, module rec, and non-recursive baseline).
• Release notes: Added entry to docs/release-notes/.FSharp.Compiler.Service/11.0.100.md.

Testing

• All 8 new regression tests pass
• All 158 existing custom attribute tests pass
• 636/638 broader conformance tests pass (2 failures are pre-existing and unrelated)

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[abonie]

@copilot Try again

[Copilot]

@copilot Try again

Implemented the fix in commit d0e2dac (with release notes in c8d283c).

Root cause: In recursive scopes (namespace rec/module rec), open declarations were only processed in Phase1AB — after Phase1A builds module entities. But module attributes need opened namespaces during Phase1A.

Fix: Added preProcessOpensForPhase1A that silently resolves opens before Phase1A attribute checking, applied at both the top level and nested module level. All 158 custom attribute tests pass, plus 8 new regression tests for issue #7931.

[github-actions]

❗ Release notes required

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

[abonie]

This test case is not reproing #5795, and in fact I think #5795 is not fixed by this PR - at the very minimum the comment should be removed

Replacing with inline comments

[T-Gro]

Review: Fix #7931 — Resolve opened namespaces for attributes in recursive scopes

APPROVE — This is a well-targeted fix for a real bug with sound approach and good test coverage.

Correctness Analysis

The root cause is correctly identified: in recursive scopes, open declarations are processed in Phase1AB (after Phase1A builds module/type entities), but module attributes are checked during Phase1A via TcAttributes cenv envInitial. The �nvInitial at that point doesn't include opened namespaces.

The fix introduces preProcessOpensForPhase1A which silently resolves opens before Phase1A. The dual-site application is correct:

1. Top-level (TcMutRecDefns_Phase1): pre-processes top-level opens into �nvWithOpens, which flows via mapWithParent as the �nvInitial parameter to TcTyconDefnCore_Phase1A_BuildInitialModule → TcAttributes for top-level modules.
2. Nested (TcTyconDefnCore_Phase1A_BuildInitialModule): pre-processes child opens into �nvForDecls, which flows via mapWithParent recursion to nested module attribute checking.

The suppressErrorReporting + TemporarilySuspendReportingTypecheckResultsToSink combination is the right pattern — errors from opens referencing not-yet-defined modules are swallowed silently, and duplicate sink entries are prevented. The proper Phase1AB processing (line 4121, via TcMutRecDefns_ComputeEnvs using the original �nvInitial) still runs with full error reporting.

Only SynOpenDeclTarget.ModuleOrNamespace is pre-processed, which is appropriate — open type declarations depend on established types and aren't relevant for attribute namespace resolution.

Tests

Good coverage with 11 test cases: core scenarios (Extension on module/type in
amespace rec, module rec, nested modules), negative tests (undefined attribute still errors, invalid open target still errors), and edge cases (multiple opens, forward-reference open, non-recursive baseline).

Minor

PR description mentions "8 test cases" but there are 11 test functions — trivial description inaccuracy.