lint: execute errcheck using ExecInDir

Execute errcheck using ExecInDir so that it will use the package of the
current buffer. It looks like it was inadvertently changed from
ExecInDir to Exec a long while ago when the exec functions were
refactored.

Add tests to verify more go#lint#Errcheck behvaviors.

Fixes #2725

autoload/go/lint.vim

@@ -223,18 +223,19 @@ endfunction
 function! go#lint#Errcheck(bang, ...) abort
   if a:0 == 0
     let l:import_path = go#package#ImportPath()
-    if import_path == -1
+    if l:import_path == -1
       call go#util#EchoError('package is not inside GOPATH src')
       return
     endif
+    let l:args = [l:import_path]
   else
-    let l:import_path = join(a:000, ' ')
+    let l:args = a:000
   endif
 
   call go#util#EchoProgress('[errcheck] analysing ...')
   redraw
 
-  let [l:out, l:err] = go#util#Exec([go#config#ErrcheckBin(), '-abspath', l:import_path])
+  let [l:out, l:err] = go#util#ExecInDir([go#config#ErrcheckBin(), '-abspath'] + l:args)
 
   let l:listtype = go#list#Type("GoErrCheck")
   if l:err != 0

autoload/go/lint_test.vim

@@ -221,7 +221,7 @@ func! Test_Lint_GOPATH() abort
 
   let expected = [
           \ {'lnum': 5, 'bufnr': bufnr('%'), 'col': 1, 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'pattern': '', 'text': 'exported function MissingDoc should have comment or be unexported'},
-          \ {'lnum': 5, 'bufnr': bufnr('%')+6, 'col': 1, 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'pattern': '', 'text': 'exported function AlsoMissingDoc should have comment or be unexported'}
+          \ {'lnum': 5, 'bufnr': bufnr('%')+5, 'col': 1, 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'pattern': '', 'text': 'exported function AlsoMissingDoc should have comment or be unexported'}
       \ ]
 
   let winnr = winnr()
@@ -249,7 +249,7 @@ func! Test_Lint_NullModule() abort
 
   let expected = [
           \ {'lnum': 5, 'bufnr': bufnr('%'), 'col': 1, 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'pattern': '', 'text': 'exported function MissingDoc should have comment or be unexported'},
-          \ {'lnum': 5, 'bufnr': bufnr('%')+6, 'col': 1, 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'pattern': '', 'text': 'exported function AlsoMissingDoc should have comment or be unexported'}
+          \ {'lnum': 5, 'bufnr': bufnr('%')+5, 'col': 1, 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'pattern': '', 'text': 'exported function AlsoMissingDoc should have comment or be unexported'}
       \ ]
 
   let winnr = winnr()
@@ -269,6 +269,51 @@ func! Test_Lint_NullModule() abort
   call gotest#assert_quickfix(actual, expected)
 endfunc
 
+func! Test_Errcheck() abort
+  let RestoreGOPATH = go#util#SetEnv('GOPATH', fnamemodify(getcwd(), ':p') . 'test-fixtures/lint')
+  silent exe 'e ' . $GOPATH . '/src/errcheck/errcheck.go'
+
+  try
+    let l:bufnr = bufnr('')
+    let expected = [
+          \ {'lnum': 9, 'bufnr': bufnr(''), 'col': 9, 'pattern': '', 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'module': '', 'text': ":\tio.Copy(os.Stdout, os.Stdin)"},
+          \ {'lnum': 10, 'bufnr': bufnr('')+1, 'col': 9, 'pattern': '', 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'module': '', 'text': ":\tio.Copy(os.Stdout, os.Stdin)"},
+        \ ]
+
+    " clear the location lists
+    call setqflist([], 'r')
+
+    call go#lint#Errcheck(1)
+
+    call gotest#assert_quickfix(getqflist(), expected)
+    call assert_equal(l:bufnr, bufnr(''))
+  finally
+    call call(RestoreGOPATH, [])
+  endtry
+endfunc
+
+func! Test_Errcheck_options() abort
+  let RestoreGOPATH = go#util#SetEnv('GOPATH', fnamemodify(getcwd(), ':p') . 'test-fixtures/lint')
+  silent exe 'e ' . $GOPATH . '/src/errcheck/errcheck.go'
+
+  try
+    let l:bufnr = bufnr('')
+    let expected = [
+          \ {'lnum': 9, 'bufnr': bufnr(''), 'col': 9, 'pattern': '', 'valid': 1, 'vcol': 0, 'nr': -1, 'type': '', 'module': '', 'text': ":\tio.Copy(os.Stdout, os.Stdin)"},
+        \ ]
+
+    " clear the location lists
+    call setqflist([], 'r')
+
+    call go#lint#Errcheck(1, '-ignoretests')
+
+    call gotest#assert_quickfix(getqflist(), expected)
+    call assert_equal(l:bufnr, bufnr(''))
+  finally
+    call call(RestoreGOPATH, [])
+  endtry
+endfunc
+
 func! Test_Errcheck_compilererror() abort
   let l:tmp = gotest#load_fixture('lint/src/errcheck/compilererror/compilererror.go')
 

autoload/go/test-fixtures/lint/src/errcheck/errcheck.go

@@ -0,0 +1,10 @@
+package errcheck
+
+import (
+	"io"
+	"os"
+)
+
+func foo() {
+	io.Copy(os.Stdout, os.Stdin)
+}

autoload/go/test-fixtures/lint/src/errcheck/errcheck_test.go

@@ -0,0 +1,11 @@
+package errcheck
+
+import (
+	"io"
+	"os"
+	"testing"
+)
+
+func TestFoo(t *testing.T) {
+	io.Copy(os.Stdout, os.Stdin)
+}