x/tools/gopls: find write (addressable aka l-value) references only

[donnol]

gopls version

Today，we can find all the references of a variable.

But I want to find the write references only.

How to do that?

Will gopls add a support to this?

var a int

// write 1
a = 1

// read 1
_ = a

// read 2
b := a

// write 2
a = 2

I want to find references to list:

a = 1
a = 2

go env

go env
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN='/home/jd/go/bin'
GOCACHE='/home/jd/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/jd/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build4068807655=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD=''
GOMODCACHE=''
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/jd/go'
GOPRIVATE=''
GOPROXY='https://goproxy.io,https://goproxy.cn,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/jd/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.3'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

find write references of a variable.

What did you see happen?

all references will list.

What did you expect to see?

only write references.

Editor and settings

No response

Logs

No response

[findleyr]

I want this feature so badly!

In fact, this is the largest reason why we filed microsoft/language-server-protocol#1911. Unfortunately, it seems to be getting no traction.

We can't do this in LSP, which means it would have to be a custom command and every client would need to implement their own logic. Nevertheless, leaving this open as a wish list item.

[ANAS727189]

I’d also find this feature very useful, and I’m interested in working on it.
Right now I’m analyzing how references are collected in gopls to understand the best way to proceed.

Before I dive deeper, would you prefer this to be prototyped as a gopls-specific command (since LSP doesn’t support write-only references yet), or should I first extend the existing references logic with write/read classification?

My thought is to include only write references (and references that are both read + write, e.g. a++), while excluding pure read references.

[findleyr]

CC @adonovan

@ANAS727189 this is a rather big project. I can give you a sense of how big:

• You'd probably want to update golang.References implement this logic, though you'll always have to include read references in the ordinary LSP references request.
• You'll need to update the xrefs index (gopls/internal/cache/xrefs) to record whether references are writes
• You'll need to add a custom command to query write references only (unfortunately, I believe with VS Code at least we don't have the ability to modify the LSP requests. @h9jiang may know better.
• You'll need to figure out a client-side UI for this command in the editor of your choice.

Nevertheless, if you would be interested in working on this, we'd support it...

[h9jiang]

From vscode-go perspective, we could use VSCode API editor.action.showReferences.

A user would be to see references using the peek reference UI

To trigger this, I think the best place would be context menu, though we can move the "Go: find write reference" right next to the "Go to references". ("Go to reference" is the LSP methods, VSCode is responsible to grouping..)

Though, we will still need to figure out how do we want to change spec to make this supported, or we can make this a custom gopls command and worry about this later.

export namespace ReferenceKind {
    /**
     * No specific access inferred (e.g. strict declarations, type signatures).
     * Value: 0
     */
    export const None = 0;

    /**
     * Reading a value (e.g. `x` in `y = x`).
     * Value: 1 (Binary: 001)
     */
    export const Read = 1;

    /**
     * Writing a value (e.g. `x` in `x = 1`).
     * Value: 2 (Binary: 010)
     */
    export const Write = 2;
}


export interface ReferenceContext {
	includeDeclaration: boolean; // existing

	/**
	 * A bitmask representing the kinds of references to include.
	 * The server should return references where the intersection of 
	 * the reference's kind and this mask is non-zero.
	 * * Example: Send `2` (Write) to find all write reference
	*/
	only?: number;
}

@adonovan

[gopherbot]

Change https://go.dev/cl/741000 mentions this issue: DNR: prrof of concept of client implementation for write only ref