Comments in empty function/loop/if-statement bodies not found

[ec-m]

Comments that are placed inside empty function, loop or if statement bodies are not found in the respective node's decorations. I would expect them to be placed somewhere in the e.g. dst.FuncDeclDecorations of the function or similarly the dst.ForStmtDecorations of the loop declaration. This snipped demonstrates the issue:

package main

func main() {
}

func empty() {
	// inside empty function, not found
}

func foo() {
	i := 1
	for i < 2 {
		// inside empty for statement, not found
	}
	// after empty for statement, found and associated with for statement

	if i == 3 {
		// inside empty if statement, not found
	}
	i = 4
}

And here you can find code to reproduce the issue: https://play.golang.org/p/Yg9OOkoP6IF [Disclaimer: sometimes the playground needs multiple tries to import all packages, so if you encounter a timeout running go build error, just execute the code again.]

I tried using dst in order to fix the issue golang/go#39753 I had with go/ast. As I am a fairly new user of this module, I might also have overlooked something - Please let me know if this is the case and how I could get the correct comment associations :) Thanks!

$ go version
go version go1.14.2 darwin/amd64

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/.../Library/Caches/go-build"
GOENV="/Users/.../Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/.../go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/.../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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/yb/hqncynqs0b5_3hyxcjpdsyr00000gr/T/go-build447564702=/tmp/go-build -gno-record-gcc-switches -fno-common"

[dave]

I'll take a look at this now...

[dave]

Yeah if there's no decoration point after the comment, it'll attach it to the previous attachment point, which in the "empty function" example is f1.Body.Decs.Lbrace.

[dave]

Same with the for statement, in forStmt.Body.Decs.Lbrace, and the if statement ifStmt.Body.Decs.Lbrace

[dave]

Take a look at positions.go in the gendst package... it shows exactly where each decoration point in on each node type. Might help track things down in future...

...

[dave]

e.g.:

	// BlockStmt(0)
	if true /*Start*/ { /*Lbrace*/
		i++
	} /*End*/

	// BlockStmt(1)
	func() /*Start*/ { /*Lbrace*/ i++ } /*End*/ ()

[dave]

The algorithm that associates comments with decoration attachment points is one of those things that doesn't have a well defined correct answer... so sometimes you get situations like this where it's not exactly straightforward.

[ec-m]

Alright, thanks for the clarification! This helps a lot :) One last thing: Does dst provide a comment map like ast.CommentMap such that I can iterate over all comments that exists and see where they are attached to? I wasn't able to find this yet but might have simply overlooked something.

[dave]

Hmm ... just been looking at this and it's not easy in a generalised way. Let me take another look...

[dave]

Yeah you'd probably want something like this:

https://play.golang.org/p/NhLPbXeTCGo

... that getDecorationInfo function is copied from here... this is a valid use case that I would like to support... so I'm considering making it public... Not sure if it belongs in the decorator package or in the dstutil package. hmm

[ec-m]

Perfect! Thanks a lot for the help :)

[dave]

Hey @ec-m, I've just released v0.25.5 which makes that helper function public in the dstutil package. See documentation here.

[ec-m]

Awesome! Thanks 👍