go/ast: Empty field docs and comments for function arguments

[index0h]

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

go version go1.13.4 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/index0h/.cache/go-build"
GOENV="/home/index0h/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/index0h/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/snap/go/4762"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/snap/go/4762/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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-build225761439=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Hi,
I tried to get comment for argument from it's func declaration, but ast.Field.Comment and ast.Field.Doc have nil values. Also, I tried the same for struct fields and comments there are exist.

package main

import (
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
)

const content = `
package my_package

func MyFunc(
	// FuncComment
	argument string,
) {}
`

func main() {
	fileSet := token.NewFileSet()
	astFile, _ := parser.ParseFile(fileSet, "main.go", content, parser.ParseComments)

	fmt.Printf("Found comment in astFile: %s\n", astFile.Comments[0].Text())

	funcArgument := astFile.Decls[0].(*ast.FuncDecl).Type.Params.List[0]
	fmt.Printf("Found doc in func argument: %s\n", funcArgument.Doc.Text())
	fmt.Printf("Found comment in func argument: %s\n", funcArgument.Comment.Text())
}

Output

Found comment in astFile: FuncComment

Found doc in func argument: 
Found comment in func argument: 

What did you expect to see?

ast.Field.Doc for func argument should contain comment if it exists in source.

What did you see instead?

Empty ast.Field.Doc and ast.Field.Comment for existed comments in source.

[agnivade]

You have to use the Comments field to get the comments.

package main

import (
	"fmt"
	"go/parser"
	"go/token"
	"log"
)

const src = `
package my_package

func MyFunc(
	// FuncComment
	argument string,
) {}

`

func main() {
	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
	if err != nil {
		log.Fatal(err)
	}

	for _, c := range f.Comments {
		fmt.Printf("%v\n", c.Text())
	}

}

Look into https://golang.org/pkg/go/ast/#CommentMap for more information.