Add basic :GoModReplace

autoload/gopher/go.vim

@@ -31,6 +31,23 @@ fun! gopher#go#module() abort
   return l:out
 endfun
 
+" Get the go.mod file location, or -1 if there is none.
+fun! gopher#go#gomod() abort
+  let l:dir = expand('%:p:h')
+  while 1
+    " len() check is for Windows; not sure how that's represented.
+    if l:dir is# '/' || len(l:dir) <= 4
+      return -1
+    endif
+
+    if filereadable(l:dir + '/go.mod')
+      return l:dir + '/go.mod'
+    endif
+
+    let l:dir = fnamemodify(l:dir, ':h')
+  endwhile
+endfun
+
 " Get the package path for the file in the current buffer.
 fun! gopher#go#package() abort
   let [l:out, l:err] = gopher#system#run(['go', 'list', './' . expand('%:h')])

autoload/gopher/mod.vim

@@ -0,0 +1,61 @@
+" mod.vim: Utilities for working with go.mod files.
+
+" Add or remove replace directives.
+fun! gopher#mod#replace(...)
+  " TODO: get arguments.
+  let l:mod = ''
+  let l:path = ''
+
+  if l:mod is# ''
+    " TODO: be a bit smarter in go.mod file, since now 'require' is considered a
+    " module as well.
+    let l:mod = expand('<cWORD>')
+  endif
+
+  if &filetype is# 'go'
+    let l:gomod = gopher#go#gomod()
+    if l:gomod is# ''
+      return gopher#error('No go.mod file found.')
+    endif
+
+    if l:mod is# ''
+      " On identifier: fmt.Printf("..")
+      if l:mod =~# '\.'
+        let l:mod = split(l:mod, '.')[0]
+        let l:resolve = gopher#pkg#resolve()
+        if l:resolve is# ''
+          return gopher#error('Unknown package: %s', l:mod)
+        endif
+
+        let l:mod = l:resolve
+      " On package: "fmt".
+      else
+        let l:mod = trim(l:mod, '"')
+      endif
+    endif
+  endif
+
+  if l:mod is# ''
+    return gopher#error('Not a package: %s', l:mod)
+  endif
+
+  if l:path is# ''
+    let l:path = '../' . fnamemodify(l:mod, ':t')
+  endif
+
+  let l:line = printf('replace %s => %s', l:mod, l:path)
+
+  " TODO: :GoModReplace on something that already exists should remove it.
+  " TODO: Don't add duplicate replaces.
+
+  " Place before first require or replace.
+  for l:i in range(1, line('$'))
+    if getline(l:i) =~# '\v^(require|replace)'
+      call append(l:i-1, [l:line, ''])
+      return
+    endif
+  endfor
+
+  " Nothing in the file yet.
+  call append('$', l:line)
+endfun

autoload/gopher/pkg.vim

@@ -37,3 +37,32 @@ fun! gopher#pkg#list_interfaces(pkg) abort
 
   return l:out
 endfun
+
+" List all imports for the current buffer.
+fun! gopher#pkg#list_imports() abort
+  let [l:out, l:err] = gopher#system#run(['go', 'list', '-f', '{{.Imports}}', expand('%')])
+  if l:err
+    call gopher#error(l:out)
+    return []
+  endif
+  return split(trim(l:out, '[]'), ' ')
+endfun
+
+" Resolve a package name to the full import path for the current buffer.
+"
+"   fmt  → fmt
+"   http → net/http
+"   pq   → github.com/lib/pq
+"
+" Returns empty string if the import is not found.
+fun! gopher#pkg#resolve(pkg) abort
+  let l:slash = '/' + a:pkg
+
+  for l:import in gopher#pkg#list_imports()
+    if l:import is# a:pkg || gopher#str#has_suffix(l:import, l:slash)
+      return l:import
+    endif
+  endfor
+
+  return ''
+endfun

doc/gopher.txt

@@ -379,10 +379,10 @@ COMMANDS                                                     *gopher-commands*
         *g:gopher_gorename_flags* = `[]`
                 List of flags to add to the `gorename` command.
 
-:GoReplace [module] [path]                                        *:GoReplace*
+:GoModReplace [module] [path]                                  *:GoModReplace*
 
-        Add a `replace` directive in the project's go.mod. This currently only
-        works in the `go.mod` buffer.
+        Add a `replace` directive in the project's go.mod. This works from any
+        `go` or the `go.mod` buffer.
 
         [module] is a module name; if it's omitted the module on the current
         line is used.

ftplugin/go.vim

@@ -109,3 +109,5 @@ command! -nargs=*        -complete=customlist,gopher#import#complete   GoImport
 command! -nargs=* -range -complete=customlist,gopher#tags#complete     GoTags     call gopher#tags#modify(<line1>, <line2>, <count>, <f-args>)
 command! -nargs=+        -complete=customlist,gopher#guru#complete     GoGuru     call gopher#guru#do(<f-args>)
 command! -nargs=?        -complete=customlist,gopher#rename#complete   GoRename   call gopher#rename#do(<f-args>)
+
+command! -nargs=* GoModReplace call gopher#mod#replace(<f-args>)

ftplugin/gomod.vim

@@ -9,3 +9,5 @@ call gopher#init#version()
 setlocal noexpandtab
 
 compiler go
+
+command! -nargs=* GoModReplace call gopher#mod#replace(<f-args>)