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Fix stale diagnostics replayed after error is resolved#12863

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copilot/fix-old-diagnostics-errors
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Fix stale diagnostics replayed after error is resolved#12863
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copilot/fix-old-diagnostics-errors

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Copilot AI commented Mar 24, 2026 •
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DKMissingFields and similar diagnostics persisted across compilations even after the underlying error was fixed, and accumulated ("stacked") with each re-run.

Root cause

add_module_diagnostic and module_warning unconditionally wrote to m.m_extra.m_cache_bound_objects. For modules loaded from the HXB binary cache (e.g. stdlib Int/StdTypes), this DynArray is shared by reference with the binary cache entry — so each diagnostics run permanently mutated the cache. handle_cache_bound_objects then replayed all accumulated stale messages on every subsequent compilation.

The key offender: displayFields.ml handle_missing_field_raise calls add_module_diagnostic with the target type's module (e.g. StdTypes for Int), while the message position is in the calling file. This embeds a usage-site diagnostic into a stdlib module's cache where it never belongs.

Changes

  • add_module_diagnostic — only writes to m_cache_bound_objects when the message position's file matches the module's own file (msg_fkey = mod_fkey). This cleanly separates intrinsic module diagnostics (e.g. interface-compliance MissingFields on c.cl_module, where c.cl_name_pos is in the module's file) from usage-site diagnostics (field-access errors whose position is in the calling file, not the target type's file).

  • module_warning — only writes to m_cache_bound_objects when m.m_extra.m_processed = 0, i.e. the module is freshly typed this compilation. Cached HXB modules have m_processed = old_step > 0 (stored via save_class_state + add_binary_cache in a prior compilation), so their shared DynArray is never mutated.

Example

function main() {
    var v = "";
    // Uncommenting the next line caused a DKMissingFields diagnostic that
    // persisted (and stacked) even after re-commenting it:
    // var v = 0;
    final char = v.charAt(0);
}

After this fix, handle_missing_field_raise no longer pollutes Int's cached m_cache_bound_objects, so the diagnostic is cleared as soon as the error is gone.

Original prompt

This section details on the original issue you should resolve

<issue_title>Old diagnostics errors are not cleared</issue_title>
<issue_description>```haxe
function main() {
var v = "";
// uncomment and comment this line:
// var v = 0;
final char = v.charAt(0);
}


Impressive regression in https://github.com/HaxeFoundation/haxe/pull/12815

</issue_description>

<agent_instructions>Please check this!</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@Simn</author><body>
I can't seem to get diagnostics anymore at all, as in vshaxe isn't sending any requests for them.</body></comment_new>
</comments>

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Copilot AI and others added 2 commits March 24, 2026 15:06
@Simn
Fix stale diagnostics not being cleared (issue #12861)
def0abe 
add_module_diagnostic now only caches the message in m_cache_bound_objects
when the message position is in the same file as the module. This prevents
the shared m_cache_bound_objects DynArray (between a module loaded from the
HXB binary cache and the cache entry itself) from being mutated by display
diagnostics whose position is in a different file (e.g. a field-access
diagnostic generated for Int's module when the access is in the user's file).

Also add the m_processed=0 guard to module_warning to prevent the same
shared-DynArray pollution for cached modules.

Adds regression test Issue12861.

Co-authored-by: Simn <634365+Simn@users.noreply.github.com>
Agent-Logs-Url: https://github.com/HaxeFoundation/haxe/sessions/cada24b6-2ee7-42e2-b413-637d30bd2312
@Simn
Fix wording in Issue12861 test comment
c82f6a6 
Co-authored-by: Simn <634365+Simn@users.noreply.github.com>
Agent-Logs-Url: https://github.com/HaxeFoundation/haxe/sessions/cada24b6-2ee7-42e2-b413-637d30bd2312
Copilot AI changed the title [WIP] Fix old diagnostics errors not cleared Fix stale diagnostics replayed after error is resolved Mar 24, 2026
Copilot AI requested a review from Simn March 24, 2026 15:09
Copilot finished work on behalf of Simn March 24, 2026 15:09
@Simn
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Simn commented Mar 24, 2026

The common.ml change makes sense, though I'm not sure if m_processed is the canonical way to check this.

The other part sounds like something else is wrong.

@Simn Simn mentioned this pull request Mar 25, 2026
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Old diagnostics errors are not cleared

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