misc/vim: fix :Import insertion heuristic.

If a factored import group has a blank line, assume it is dividing
separate groups of imports (e.g. standard library vs. site-specific).
        import (
                "bytes"
                "io"

                "mycorp/package"
        )

The most common case is inserting new standard library imports,
which are usually (stylistically) the first group, so we should drop
"net" in the above example immediately after "io".

Since this logic is getting non-trivial, add a test.

R=golang-dev, minux.ma, franciscossouza
CC=golang-dev
https://golang.org/cl/6445043

misc/vim/ftplugin/go/import.vim

@@ -12,7 +12,7 @@
 "       in the current Go buffer, using proper style and ordering.
 "       If {path} is already being imported, an error will be
 "       displayed and the buffer will be untouched.
-" 
+"
 "   :ImportAs {localname} {path}
 "
 "       Same as Import, but uses a custom local name for the package.
@@ -58,6 +58,12 @@ function! s:SwitchImport(enabled, localname, path)
         return
     endif
 
+    " Extract any site prefix (e.g. github.com/).
+    " If other imports with the same prefix are grouped separately,
+    " we will add this new import with them.
+    " Only up to and including the first slash is used.
+    let siteprefix = matchstr(path, "^[^/]*/")
+
     let qpath = '"' . path . '"'
     if a:localname != ''
         let qlocalpath = a:localname . ' ' . qpath
@@ -83,16 +89,31 @@ function! s:SwitchImport(enabled, localname, path)
             let appendstr = qlocalpath
             let indentstr = 1
             let appendline = line
+            let firstblank = -1
+            let lastprefix = ""
             while line <= line("$")
                 let line = line + 1
                 let linestr = getline(line)
                 let m = matchlist(getline(line), '^\()\|\(\s\+\)\(\S*\s*\)"\(.\+\)"\)')
                 if empty(m)
+                    if siteprefix == ""
+                        " must be in the first group
+                        break
+                    endif
+                    " record this position, but keep looking
+                    if firstblank < 0
+                        let firstblank = line
+                    endif
                     continue
                 endif
                 if m[1] == ')'
+                    " if there's no match, add it to the first group
+                    if appendline < 0 && firstblank >= 0
+                        let appendline = firstblank
+                    endif
                     break
                 endif
+                let lastprefix = matchstr(m[4], "^[^/]*/")
                 if a:localname != '' && m[3] != ''
                     let qlocalpath = printf('%-' . (len(m[3])-1) . 's %s', a:localname, qpath)
                 endif
@@ -103,7 +124,16 @@ function! s:SwitchImport(enabled, localname, path)
                     let deleteline = line
                     break
                 elseif m[4] < path
-                    let appendline = line
+                    " don't set candidate position if we have a site prefix,
+                    " we've passed a blank line, and this doesn't share the same
+                    " site prefix.
+                    if siteprefix == "" || firstblank < 0 || match(m[4], "^" . siteprefix) >= 0
+                        let appendline = line
+                    endif
+                elseif siteprefix != "" && match(m[4], "^" . siteprefix) >= 0
+                    " first entry of site group
+                    let appendline = line - 1
+                    break
                 endif
             endwhile
             break

misc/vim/ftplugin/go/test.sh

@@ -0,0 +1,61 @@
+#!/bin/bash -e
+#
+# Copyright 2012 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+#
+# Tests for import.vim.
+
+cd $(dirname $0)
+
+cat > base.go <<EOF
+package test
+
+import (
+	"bytes"
+	"io"
+	"net"
+
+	"mycorp/foo"
+)
+EOF
+
+fail=0
+
+# usage: test_one new_import pattern
+# Pattern is a PCRE expression that will match across lines.
+test_one() {
+  echo 2>&1 -n "Import $1: "
+  vim -e -s -u /dev/null -U /dev/null --noplugin -c "source import.vim" \
+    -c "Import $1" -c 'wq! test.go' base.go
+  # ensure blank lines are treated correctly
+  if ! gofmt test.go | cmp test.go; then
+    echo 2>&1 "gofmt conflict"
+    gofmt test.go | diff -u test.go - | sed "s/^/\t/" 2>&1
+    fail=1
+    return
+  fi
+  if ! grep -P -q "(?s)$2" test.go; then
+    echo 2>&1 "$2 did not match"
+    cat test.go | sed "s/^/\t/" 2>&1
+    fail=1
+    return
+  fi
+  echo 2>&1 "ok"
+}
+
+test_one baz '"baz".*"bytes"'
+test_one io/ioutil '"io".*"io/ioutil".*"net"'
+test_one myc '"io".*"myc".*"net"'  # prefix of a site prefix
+test_one nat '"io".*"nat".*"net"'
+test_one net/http '"net".*"net/http".*"mycorp/foo"'
+test_one zoo '"net".*"zoo".*"mycorp/foo"'
+test_one mycorp/bar '"net".*"mycorp/bar".*"mycorp/foo"'
+test_one mycorp/goo '"net".*"mycorp/foo".*"mycorp/goo"'
+
+rm -f base.go test.go
+if [ $fail -gt 0 ]; then
+  echo 2>&1 "FAIL"
+  exit 1
+fi
+echo 2>&1 "PASS"