x/tools/gopls: fails to generate proper func signature when autocompleting parameters for generic functions

[igadmg]

What version of Go, VS Code & VS Code Go extension are you using?

Version Information

• Run go version to get version of Go from the VS Code integrated terminal.
  • go version go1.26.2 windows/amd64
• Run gopls -v version to get version of Gopls from the VS Code integrated terminal.
  • golang.org/x/tools/gopls v0.21.1
• Run code -v or code-insiders -v to get version of VS Code or VS Code Insiders.
  • Version: 1.118.1 (system setup)
• Check your installed extensions to get the version of the VS Code Go extension
  • 0.52.2

Share the Go related settings you have added/edited

Describe the bug

When autocompleting code for parameters to functions reveiving functions vs code fails to figure out parameters.
For example

	var s []int
	slices.SortFunc(s, func() int {})

So instead of figuring out that func() int should accept parameters a,b int vs code fails to do so.
Expected to have autocomplete of

	var s []int
	slices.SortFunc(s, func(a, b, int) int {})

PS: it feels that at some stage long ago it was working and then was broken maybe half year ago or so.

[madelinekalil]

Hi! Can you please share your gopls settings? I'm assuming you must have "ui.completion.usePlaceholders": true,
However, I am not able to reproduce this. I get the following completion for slices.SortFunc:
slices.SortFunc(x S, cmp func(a E, b E) int)

[igadmg]

I have only that in vscode settings

    "gopls": {
        "ui.semanticTokens": true
    },

[igadmg]

main.go.-.test.-.Visual.Studio.Code.2026-05-04.17-45-19.mp4

Here is video in new empty project without any specific gopls settings.

[madelinekalil]

Thanks, I understand now and am able to reproduce, although the behavior is inconsistent. Moving this issue to gopls

[gabyhelp]

Related Issues

• x/tools/gopls: For generic function completion, don't complete with `Name[|]()` if type parameters can be inferred #72758
• x/tools/gopls: completion gives wrong lambda suggestion for pointer receivers of a generic type #61189 (closed)
• x/tools/gopls: reverse type inference for completions in generic function call params #69754 (closed)
• x/tools/gopls: support type parameters for function literal snippet completions #50623 (closed)
• x/tools/gopls: add autocomplete for generic function type aliases #52291
• x/tools/gopls: add type parameters/placeholders in function calls #51544 (closed)
• x/tools/gopls: completion and quick fix for filling in type parameters in generic types #64501
• x/tools/gopls: no completion for function literal in parameter #38416 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/783740 mentions this issue: gopls/internal/golang: fix completion when generic fu Result isn't free

[xieyuschen]

Offered a fix, please kindly assign the issue to me.