Offer every open that resolves the name, and open type where a plain open cannot reach

[xperiandri]

Stacked on #20500 — the first commit here is that PR. Review the last three.

Two defects in what the "open namespace" code fix suggests, both visible on the same example: an unresolved File in File.ReadAllText "x".

A plain open was offered for things it cannot reach

A plain open takes namespaces and F# modules. The fix offered one for every candidate it found, so File was answered with open System.Net.WebRequestMethods and an unresolved WriteLine with open System.Console — code that does not compile, FS0039: The namespace 'WebRequestMethods' is not defined, because those name types, and a type's nested types and static members are only brought into scope by open type.

Nothing in the entity model told the two apart: the namespace to open was the dotted name of the candidate's container, whatever kind of thing that container was. AssemblySymbol now records how far a plain open reaches — the namespace, extended by each enclosing F# module — and InsertionContextEntity how much of the candidate's name the suggested open covers, which the qualification already written at the use site and auto-open modules can both shorten. The fix compares the two and writes open type when the suggestion reaches past what a plain open can.

Only one suggestion was ever offered

The fix computed a suggestion for every namespace and type a name could be resolved from, and then Seq.tryHead threw all but one away — whichever one the assembly crawler happened to reach first. File was answered with System.Net.WebRequestMethods and never with System.IO.

IFSharpMultiCodeFixProvider already exists for providers with more than one suggestion, so the provider implements that instead and registers them all. Following Roslyn's AbstractAddImportCodeFixProvider, which faces the same problem:

• the list is capped — five opens and three qualifications, against Roslyn's MaxResults of 5 and its fully-qualify's 3 — because a lightbulb is a menu somebody reads;
• it is ordered with what System holds first (Roslyn's placeSystemNamespaceFirst: true) rather than by the order the crawler walked the assemblies in. Without that, Microsoft.VisualBasic.FileSystem sorts above System.Console for WriteLine.

Tests

AddOpenOnTopOnTests/AddOpenOnTopOffTests now assert the whole list of suggestions rather than one, with cases for a name reachable from two namespaces, a static member reachable from four types, and the qualifications offered after the opens.

🤖 Generated with Claude Code

[github-actions]

❗ Release notes required

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Change path	Release notes path	Description
`src/Compiler`	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md	No current pull request URL (#20501) found, please consider adding it
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md	No current pull request URL (#20501) found, please consider adding it

[xperiandri]

[github-actions]

🔍 Tooling Safety Check — Affects-Design-Time
Affects-Design-Time: IDE code-fix logic executes during design-time analysis.

Generated by PR Tooling Safety Check · gpt56 2.6M · ◷

[T-Gro]

🤖 🕵️ AI review — verify independently.

[T-Gro]

🤖 🕵️ [P2] Choosing N.M.FixTarget817 rewrites M.FixTarget817() to M.N.M() (FS0039). Replace the matching long-identifier prefix, not just the diagnostic span.

module Review
module M = let marker = ()
module N =
    module M =
        type FixTarget817() = class end
let x = M.FixTarget817()