eliminate errors trying to run a command in a directory that does not exist

autoload/go/tool.vim

@@ -162,6 +162,18 @@ function! go#tool#FilterValids(items) abort
 endfunction
 
 function! go#tool#ExecuteInDir(cmd) abort
+  " Verify that the directory actually exists. If the directory does not
+  " exist, then assume that the a:cmd should not be executed. Callers expect
+  " to check v:shell_error (via go#util#ShellError()), so execute a command
+  " that will return an error as if a:cmd was run and exited with an error.
+  " This helps avoid errors when working with plugins that use virtual files
+  " that don't actually exist on the file system (e.g. vim-fugitive's
+  " GitDiff).
+  if !isdirectory(expand("%:p:h"))
+    let [out, err] = go#util#Exec(["false"])
+    return ''
+  endif
+
   let old_gopath = $GOPATH
   let old_goroot = $GOROOT
   let $GOPATH = go#path#Detect()

autoload/go/tool_test.vim

@@ -0,0 +1,23 @@
+func! Test_ExecuteInDir() abort
+  let l:tmp = gotest#write_file('a/a.go', ['package a'])
+  try
+    let l:out = go#tool#ExecuteInDir("pwd")
+    call assert_equal(l:tmp . "/src/a\n", l:out)
+  finally
+    call delete(l:tmp, 'rf')
+  endtry
+endfunc
+
+func! Test_ExecuteInDir_nodir() abort
+  let l:tmp = go#util#tempdir("executeindir")
+  exe ':e ' . l:tmp . '/new-dir/a'
+
+  try
+    let l:out = go#tool#ExecuteInDir("pwd")
+    call assert_equal('', l:out)
+  finally
+    call delete(l:tmp, 'rf')
+  endtry
+endfunc
+
+" vim: sw=2 ts=2 et