Support CallerArgumentExpression

[ijklam]

Description

Implements fsharp/fslang-suggestions#966, #18489

RFC FS-1149-support-CallerArgumentExpression.md, FS-1332-assert-keyword-enhancement.md

Checklist

• Test cases added
• Performance benchmarks added in case of performance changes
• Release notes entry updated:

[github-actions]

❗ Release notes required

@ijklam,

Caution

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Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md	No release notes found or release notes format is not correct

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
LanguageFeatures.fsi	docs/release-notes/.Language/preview.md

[ijklam]

Here I encounter a problem about #line. For example, the code is saved in D:\Program.fs:

#1 "C:\\Program.fs"
System.ArgumentNullException.ThrowIfNullOrWhiteSpace("   ")  // will failed to build

// And more complicated case, repeat the file name and line number
#1 "C:\\Program.fs"
System.ArgumentNullException.ThrowIfNullOrWhiteSpace("   ")  // will failed to build

So here I want to get the original range instead of a range modified by #line . Is there anybody know how to do it?

[brianrourkeboll]

I wonder whether it would be possible to use ISourceText.GetSubTextString instead of all of this. I think the ISourceText for a given file will usually already be cached when this functionality is needed.

I think in theory the source text is available on cenv.tcSink.CurrentSink.Value.CurrentSourceText.Value, but maybe there's a better way to get it, or a better way to bring it in scope for this change.

[ijklam]

It seems that this cannot work under dotnet fsi and under dotnet build. It is always None.

[brianrourkeboll]

Maybe it would make sense to pass it in, then, as is done when checking format strings:

fsharp/src/Compiler/Checking/NameResolution.fs

Lines 1777 to 1779 in 0a715a5

	type FormatStringCheckContext =
	{ SourceText: ISourceText
	LineStartPositions: int[] }

fsharp/src/Compiler/Checking/CheckFormatStrings.fs

Lines 67 to 73 in 0a715a5

	let makeFmts (context: FormatStringCheckContext) (fragRanges: range list) (fmt: string) =
	// Splits the string on interpolation holes based on fragment ranges.
	// Returns a list of tuples in the form of: offset * fragment as a string * original range of the fragment
	// where "offset" is the offset between beginning of the original range and where the string content begins
	let numFrags = fragRanges.Length
	let sourceText = context.SourceText

[brianrourkeboll]

Maybe it would make sense to pass it in, then, as is done when checking format strings:

I guess maybe that's the same source text as in the sink... But still, maybe there's somewhere else we could put it.

[ijklam]

@T-Gro Hi there, I cannot access the Azure to see the test result. Could you please grant me the permission?

The page said:

The selected user account does not exist in the tenant "Microsoft" and cannot access the application "499b84ac-1321-427f-aa17-267ca6975798" in that tenant. You need to add the account as an external user of the tenant first. Please use a different account.

[majocha]

@ijklam I see there are some timeouts in .Net Framework test runs, probably the cause is this #18875, so unrelated to your code. (threadpool starvation likely).

[Copilot]

Pull request overview

This PR implements support for the CallerArgumentExpression attribute in F#, as specified in RFC FS-1149. The feature allows method parameters to capture the source code text of arguments passed at call sites, similar to the C# feature. Additionally, it enhances the assert keyword to automatically pass the assertion expression as a string parameter when available.

Changes:

• Adds CallerArgumentExpression as a new language feature and caller info type
• Implements source text tracking in lexbuf and throughout the compilation pipeline
• Updates method call resolution to pass argument expression text to annotated parameters
• Enhances assert expressions to pass expression text to Debug.Assert methods
• Adds comprehensive tests for various scenarios including F#/C# interop, computation expressions, and edge cases

Reviewed changes

Copilot reviewed 48 out of 49 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Compiler/Facilities/LanguageFeatures.fs/fsi	Adds SupportCallerArgumentExpression feature flag
src/Compiler/Facilities/prim-lexing.fs/fsi	Adds SourceText tracking to LexBuffer for capturing source code
src/Compiler/TypedTree/TcGlobals.fs/fsi	Adds attrib_CallerArgumentExpressionAttribute to supported attributes
src/Compiler/TypedTree/TypedTreeOps.fs/fsi	Adds helpers to find attributes by name for user-defined CallerArgumentExpression
src/Compiler/Checking/infos.fs/fsi	Extends CallerInfo DU with CallerArgumentExpression case and implements precedence logic
src/Compiler/Checking/MethodCalls.fs/fsi	Implements argument expression text capture and passing to optional parameters
src/Compiler/Checking/CheckExpressions.fs	Enhances assert to pass expression text as second argument
src/Compiler/Checking/PostInferenceChecks.fs	Adds validation for CallerArgumentExpression parameters
src/Compiler/Checking/CheckDeclarations.fs/fsi	Threads source text through checking pipeline
src/Compiler/Checking/CheckBasics.fs/fsi	Adds SourceText field to TcFileState
src/Compiler/Driver/ParseAndCheckInputs.fs/fsi	Updates signatures to carry source text with parsed inputs
src/Compiler/Driver/fsc.fs	Updates driver to handle source text in inputs
src/Compiler/Driver/ScriptClosure.fs/fsi	Adds source text tracking to load closures
src/Compiler/Service/*	Updates service layer to thread source text through APIs
src/Compiler/Interactive/fsi.fs	Updates FSI to support CallerArgumentExpression in interactive scenarios
src/Compiler/FSComp.txt	Adds new diagnostic messages for CallerArgumentExpression feature
src/Compiler/xlf/*.xlf	Adds localization strings for new diagnostics
tests/FSharp.Compiler.ComponentTests/ErrorMessages/UnsupportedAttributes.fs	Removes CallerArgumentExpression from unsupported list
tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/CustomAttributes/CallerArgumentExpression/CallerArgumentExpression.fs	Comprehensive tests for the feature
tests/FSharp.Compiler.ComponentTests/Conformance/Expressions/ApplicationExpressions/AssertExpression.fs	Tests for enhanced assert expressions
docs/release-notes/*	Documents the new feature

[ijklam]

It needs modify the parser to make it knows the this parameter of an F# style extension method (like this).

type System.Object with
   member this.A([<CallerArgumentExpression "this">] ?arg: string) = arg
       // ^^^^                               ^^^^

I tried make it stores the this parameter name during the parsing, but it will break the other parts of compilation. (for example, it will report xmlDocMissingParameter error for this parameter)

fsharp/src/Compiler/SyntaxTree/SyntaxTreeOps.fs

Lines 735 to 746 in c33bedd

	let selfMetadata =
	match pat with
	| Some(SynPat.LongIdent(longDotId = SynLongIdent(id = ident :: _))) -> [ SynArgInfo([], false, Some ident) ]
	| _ -> selfMetadata
	let infosForObjArgs = if memFlags.IsInstance then [ selfMetadata ] else []
	let infosForArgs = AdjustMemberArgs memFlags.MemberKind infosForExplicitArgs
	let infosForArgs = AdjustArgsForUnitElimination infosForArgs
	let argInfos = infosForObjArgs @ infosForArgs
	SynValData(Some memFlags, SynValInfo(argInfos, retInfo), None)