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go/format: format.Source errors on seemingly correct code; doesn't provide details #42172

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jadekler opened this issue Oct 23, 2020 · 2 comments

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@jadekler
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What version of Go are you using (go version)?

$ go version
go version go1.15.3 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/deklerk/.cache/go-build"
GOENV="/home/deklerk/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/deklerk/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/deklerk/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/deklerk/workspace/tools/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build692544628=/tmp/go-build -gno-record-gcc-switches"

What did you do?

	secondFormat, err := format.Source(firstPass)
	if err != nil {
		return nil, fmt.Errorf("failed to run second format on:\n%s\ngot err: %v", string(firstPass), err)
	}

As part of https://go-review.googlesource.com/c/tools/+/262018, on,

        {
        		ValuePos: 0,
        		Kind:     0,
        		Value:    "",
        	}

What did you expect to see?

{
	ValuePos: 0,
	Kind:     0,
	Value:    "",
}

What did you see instead?

    lsp_test.go:535: error converting command "gopls.fill_struct" to edits: error calling command.SuggestedFix: failed to run second format on:
        {
        		ValuePos: 0,
        		Kind:     0,
        		Value:    "",
        	}
        got err: 2:13: expected 1 expression (and 2 more errors)

My question: why does format.Source blow up on this code? And, what does expected 1 expression mean - isn't what I passed in an expression [1]? And, what are the other 2 errors?

1: I'm not particularly well versed on the nouns that comprise a programming language - sorry!

@stamblerre
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You can think of an expression here as any AST node that implements ast.Expr. I often use http://goast.yuroyoro.net/ to inspect the Go AST and understand it better. In this case, you've written an ast.CompositeLit without the Type field before the curly brace (Lbrace), so the expression does not parse.

@jadekler
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Thank you!

@golang golang locked and limited conversation to collaborators Oct 23, 2021
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