x/tools/gopls: bad completion with syntax errors

[kzhui125]

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

• Run go version to get version of Go
  • go version go1.14.3 darwin/amd64
• Run code -v or code-insiders -v to get version of VS Code or VS Code Insiders
  • 1.46.0
  • a5d1cc28bb5da32ec67e86cc50f84c67cc690321
  • x64
• Check your installed extensions to get the version of the VS Code Go extension
  • 0.14.4

full code:

package main

import "fmt"

type result struct {
	value interface{}
	err   error
}

func getResult() (interface{}, error) {
	return "test", nil
}

func main() {
	var res result
	res.value, res.err = getResult()
	fmt.Println(res)
}

When I type "res.", I expect "err" will appear.

But now the code completion stop working, I have to type "err" manually.

Please fix the bug, thanks.

[kzhui125]

another problem: when I type tab here, I expect "getResult()" will appear, but only "getResult" appear now.

[hyangah]

@kzhui125 Thanks for the issue report.
Can you please run Preferences: Open Settings (JSON) command and Preferences: Open Workspace Settings (JSON) and share all the settings with the go. or ["go"] or gopls prefixes?

[kzhui125]

    "files.autoSave": "afterDelay",
    "files.autoSaveDelay": 300,
    "[golang]": {
        "editor.tabSize": 4,
        "editor.detectIndentation": false,
        "editor.insertSpaces": false,
    },
    "go.delveConfig": {
        "dlvLoadConfig": {
            "followPointers": true,
            "maxVariableRecurse": 1,
            "maxStringLen": 100000,
            "maxArrayValues": 1000,
            "maxStructFields": -1
        },
        "apiVersion": 2,
        "showGlobalVariables": true
    },
    "go.formatTool": "goimports",
    "go.useLanguageServer": true,
    "go.testFlags": [
        "-v"
    ],
    "go.languageServerFlags": [
        "-rpc.trace",
    ],
    "[go]": {
        "editor.formatOnSave": true,
        "editor.codeActionsOnSave": {
            "source.organizeImports": true,
        },
    },
    "[go.mod]": {
        "editor.formatOnSave": true,
        "editor.codeActionsOnSave": {
            "source.organizeImports": true,
        },
    },
    "gopls": {
        "usePlaceholders": true,
        "completeUnimported": true
    },

[kzhui125]

[hyangah]

Thanks @kzhui125!
/cc @stamblerre Can you please take a look and triage in gopls issue tracker? This issue discusses two symptoms and I guess the underlying problem is similar to #38600.

1. missing completion.
2. missing () even though "usePlaceholders": true is selected.

[findleyr]

Just took a look at this. Unlike many of the other completion issues that can be fixed with improved parser error recovery, I don't think this can be done with go/parser alone. There's no obvious way to represent this (invalid) syntax in a valid syntax tree.

Perhaps we could have some basic fallback that looks for a preceding selector on an identifier, and then evaluate that identifier in the appropriate scope. I'm not sure how much that technique would generalize, so I'm not convinced it's worth doing.

[adonovan]

I expect this case is so common that it may be worth special casing in gopl's additional recovery (fixAST). In the above example, the sequence [period, newline, "outdent"] is a good sign that the current line is incomplete. It could be repaired to SelectorExpr(Ident("res"), Ident("")).