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Import: Don't walk non-F# assemblies when labelling trait constraint sources (#20090)
* Don't walk non-F# assemblies when labelling trait constraint sources `addConstraintSources` (added in #16304, so that a failed member constraint names the member it came from) is applied to every imported assembly, and recurses through `e.ModuleOrNamespaceType` for every module and namespace entity it finds. For an assembly imported from IL there is nothing to find: the walk only reads `AllValsAndMembers`, and `ImportILTypeDefs` gives every namespace and type entity an empty val list; only an F# trait constraint produces a `TyparConstraint.MayResolveMember` to label in the first place. Meanwhile the recursion forces each namespace entity's `ModuleOrNamespaceType`, which imports that namespace - so referencing an assembly ends up importing every namespace in it, and reading every type definition, whether or not the code touches it. Skip the CCUs that aren't F#. FSharp.Core and F# references are still walked, so the error messages are unchanged. Measured with FSharpChecker.ParseAndCheckProject, keeping the results alive so the imported assembly structures stay on the heap (averages of 3 runs, one per process): a 486-reference F# project retains 1319.2 -> 952.1 MB (-27.8%), and a 168-reference console project 77.7 -> 69.8 MB (-10.2%). Checking FSharp.Compiler.Service itself (124 references, 397 sources) goes 2301.7 -> 2298.0 MB, i.e. within the noise at that size - what the imports cost there is dwarfed by the trees of the project's own code.
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‎docs/release-notes/.FSharp.Compiler.Service/11.0.100.md‎

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* Fix dot-completion after indexed expressions (`a.[0].Data.`, `a[0].Data.`, `[1;2].Length.`) returning unrelated global completions instead of expression-typings members. ([Issue #4966](https://github.com/dotnet/fsharp/issues/4966), [PR #19934](https://github.com/dotnet/fsharp/pull/19934))
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* Quotations of `match s with "" -> _` no longer leak the `s <> null && s.Length = 0` lowering; the empty-string optimization moved from pattern-match compilation to the optimizer so quoted expressions keep `op_Equality(s, "")`. ([Issue #19873](https://github.com/dotnet/fsharp/issues/19873))
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* Fix #5795: Allow attributes defined in a `module rec` / `namespace rec` scope to be used on union cases, record fields, and generic type parameters of types in the same recursive scope. ([Issue #5795](https://github.com/dotnet/fsharp/issues/5795), [PR #19744](https://github.com/dotnet/fsharp/pull/19744))
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* Import: Don't walk non-F# assemblies when labelling trait constraint sources (PR [#20090](https://github.com/dotnet/fsharp/pull/20090))
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### Added
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‎src/Compiler/Driver/CompilerImports.fs‎

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let! ccuinfos = phase2s |> runMethod
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if importsBase.IsSome then
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let addConstraintSources (ia: ImportedAssembly) =
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// Only an F# assembly can carry a trait constraint to label.
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// Prevent force-reading of the whole assembly namespace tree for other assemblies.
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if ia.FSharpViewOfMetadata.IsFSharp then
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addConstraintSources ia
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importsBase.Value.CcuTable.Values |> Seq.iter addConstraintSources
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ccuTable.Values |> Seq.iter addConstraintSources
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