cmd/go: update -trimpath documentation

[hyangah]

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

$ go version
go1.18beta1

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/hakim/Library/Caches/go-build"
GOENV="/Users/hakim/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/hakim/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/hakim/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/hakim/sdk/go1.18beta1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/hakim/sdk/go1.18beta1/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18beta1"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/hakim/ww/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/bw/6r6k9d113sv1_vvzk_1kfxbm001py5/T/go-build1609535835=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Built the following program with -trimpath ( % go build -trimpath -o out )

--- go.mod ---
module work

go 1.17

require golang.org/x/mod v0.5.1

--- main.go ---
package main

import (
        "golang.org/x/mod/semver"
)

func main() {
        if semver.IsValid("1.0.0") {
                println("valid")
        }
}

What did you expect to see?

As described in go1.18beta1 help build, expected to see files from standard packages start with "go"

    -trimpath
            remove all file system paths from the resulting executable.
            Instead of absolute file system paths, the recorded file names
            will begin with either "go" (for the standard library),
            or a module path@version (when using modules),
            or a plain import path (when using GOPATH).

What did you see instead?

Files from standard libraries without "go" (plain import path + file base name)

% strings out | grep map.go
runtime/mbitmap.go
runtime/map.go

Description for packages from dependency modules seems correct.

% strings out | grep semver.go
golang.org/x/[email protected]/semver/semver.go

Maybe need to mention behavior for main module files explicitly.

% strings out | grep main.go  
work/main.go

[cagedmantis]

/cc @bcmills @matloob

[gopherbot]

Change https://golang.org/cl/380078 mentions this issue: cmd/go: correct -trimpath docs for the standard library

[mpx]

Drafted a change. I haven't mentioned the "main" module since the behaviour depends on how it is built:

• go build / go install will not have a version (like GOPATH)
• go install full.path@latest will include the @ version.

Suggestions for concise terminology?