Lack of error from language service masks build error in error list #6036

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1. cartermp

   added

   Bug

   Area-LangService-API

   on Dec 19, 2018
2. cartermp

   added this to the 16.0 milestone on Dec 19, 2018
3. cartermp

   modified the milestones: 16.0, 16.1 on Feb 21, 2019
4. cartermp

   modified the milestones: 16.1, 16.2 on Apr 23, 2019
5. cartermp

   modified the milestones: 16.2, Backlog on Apr 30, 2019
6. dsyme

   added

   Impact-Low(Internal MS Team use only) Describes an issue with limited impact on existing code.(Internal MS Team use only) Describes an issue with limited impact on existing code.

   on Aug 26, 2020
7. cartermp

   modified the milestones: Backlog, Backlog - Lower Priority on Aug 26, 2020
8. cartermp

   modified the milestones: Backlog - Lower Priority, Backlog on Oct 28, 2020
9. dsyme

   added

   Impact-Medium(Internal MS Team use only) Describes an issue with moderate impact on existing code.(Internal MS Team use only) Describes an issue with moderate impact on existing code.

   and removed

   Impact-Low(Internal MS Team use only) Describes an issue with limited impact on existing code.(Internal MS Team use only) Describes an issue with limited impact on existing code.

   on Apr 5, 2022
10. dsyme commented on Apr 5, 2022

    

    dsyme

    on Apr 5, 2022

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    This is actually a pretty significant bug. Even in F# 2.0 a failure in correct diagnostic list unification between intellisense and build diagnostics would have been considered a high-priority bug.

    I think I've seen often too (Since about VS2015 I've learned not to trust the "Build + Intellisense" to show me build errors)
11. dsyme

    added

    Area-LangService-DiagnosticsFCS code analysis, diagnostics, red squiggliesFCS code analysis, diagnostics, red squigglies

    and removed

    Area-LangService-API

    on Apr 5, 2022
12. vzarytovskii

    added this to F# Compiler and Toolingon Jun 17, 2022
13. vzarytovskii

    moved this to Not Planned in F# Compiler and Toolingon Jun 17, 2022
14. github-actions

    added

    AI-thinks-windows-only

    on Mar 16, 2026
15. github-actions

    added

    AI-thinks-issue-fixed

    and removed

    AI-thinks-windows-only

    on Oct 6, 2026
16. github-actions commented on Oct 6, 2026

    

    github-actionsbot

    on Oct 6, 2026 – with GitHub Actions

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    🤖 This is an automated response from Repo Assist.

    This is not Windows-only: the diagnostic source is FSharp.Compiler.Service project checking, which is cross-platform. I removed AI-thinks-windows-only.

    I rebuilt from 0dee96c8c6b15aa1afdb866c4d3b498579528d77 (2026-10-06). The fresh FSI reports 15.2.200.0 for F# 11.2, FSharp.Core 11.0.0.0, and .NET 11.0.0-rc.1.26420.103. Using the freshly produced FCS assembly, I ran FSharpChecker.ParseAndCheckProject on the exact two-file repro from #6035. It now returns:

    FS0247 The name 'A.B' is used as both a namespace and a module in this assembly. Rename one of them to avoid the conflict.
    

    The missing IntelliSense diagnostic therefore no longer reproduces, so I applied AI-thinks-issue-fixed. I am adding an FCS regression test that checks this project-level diagnostic directly.

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17. github-actions

    removed

    AI-thinks-issue-fixed

    on Oct 6, 2026
18. github-actions commented on Oct 6, 2026

    

    github-actionsbot

    on Oct 6, 2026 – with GitHub Actions

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    🤖 This is an automated response from Regression PR Shepherd.

    Issue still reproduces. Regression test in #20706 confirms it: with the transparent compiler enabled, ParseAndCheckProject returns no diagnostics and Array.exactlyOne fails with The input sequence was empty. Apologies for the incorrect label.

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    Generated by Regression PR Shepherd · gpt56 3M · ◷
19. T-Gro

    added a commit that references this issue on Oct 9, 2026

    Add regression test: #6036, FCS namespace-module collision diagnostic (…

    ...

    81fbc52
20. T-Gro

    closed this as completedin #20706on Oct 9, 2026