feat: absolute imports (#63)

* feat: go-like import style

jb now creates a directory structure inside of vendor/ that is similar to how go
does (github.com/grafana/jsonnet-libs). This is reflected in the final import
paths, which means they will be go-like

* refactor(spec/deps): named regexs

* feat: make goImportStyle configurable

Defaults to off, can be enabled in `jsonnetfile.json`

* fix: integration test

* doc: license headers

* fix(deps): remove GO_IMPORT_STYLE

not an option anymore, will always do so and symlink

* feat: symlink to legacy location

* feat: allow to disable legacy links

* fix(test): legacyImports in integration tests

* fix(spec): test

* fix: respect legacyName aliases

It was possible to alias packages by changing `name` previously.

While names are now absolute (and computed), legacy links should still respect
old aliases to avoid breaking code.

* fix(test): integration

* fix(init): keep legacyImports enabled for now

* feat: rewrite imports

adds a command to automatically rewrite imports from legacy to absolute style

* fix(tool): rewrite confused by prefixing packages

When a package was a prefix of another one, it broke.
Fixed that by using a proper regular expression. Added a test to make sure it
works as expected

* Update cmd/jb/init.go

* fix: exclude local packages from legacy linking

They actually still use the old style, which is fine. LegacyLinking
messed them up, but from now on it just ignores symlinks that match a localPackage.

tool/rewrite/rewrite_test.go

@@ -0,0 +1,76 @@
+// Copyright 2018 jsonnet-bundler authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package rewrite
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/jsonnet-bundler/jsonnet-bundler/spec/deps"
+)
+
+const sample = `
+(import "k.libsonnet") + // not vendored
+(import "ksonnet/abc.jsonnet") + // prefix of next
+(import "ksonnet.beta.4/k.libsonnet") + // normal import
+(import "github.com/ksonnet/ksonnet/def.jsonnet") + // already absolute
+(import "prometheus/mixin/whatever/abc.libsonnet") + // nested
+(import "mylib/foo.libsonnet") + // not managed by jb
+// completely unrelated line:
+[ "nice" ]
+`
+
+const want = `
+(import "k.libsonnet") + // not vendored
+(import "github.com/ksonnet/ksonnet/abc.jsonnet") + // prefix of next
+(import "github.com/ksonnet/ksonnet-lib/ksonnet.beta.4/k.libsonnet") + // normal import
+(import "github.com/ksonnet/ksonnet/def.jsonnet") + // already absolute
+(import "github.com/prometheus/prometheus/mixin/whatever/abc.libsonnet") + // nested
+(import "mylib/foo.libsonnet") + // not managed by jb
+// completely unrelated line:
+[ "nice" ]
+`
+
+func TestRewrite(t *testing.T) {
+	dir, err := ioutil.TempDir("", "jbrewrite")
+	require.Nil(t, err)
+	defer os.RemoveAll(dir)
+
+	name := filepath.Join(dir, "test.jsonnet")
+	err = ioutil.WriteFile(name, []byte(sample), 0644)
+	require.Nil(t, err)
+
+	vendorDir := filepath.Join(dir, "vendor")
+	err = os.MkdirAll(vendorDir, os.ModePerm)
+	require.Nil(t, err)
+
+	err = Rewrite(dir, "vendor", locks)
+	require.Nil(t, err)
+
+	content, err := ioutil.ReadFile(name)
+	require.Nil(t, err)
+
+	assert.Equal(t, want, string(content))
+}
+
+var locks = map[string]deps.Dependency{
+	"ksonnet":        *deps.Parse("", "github.com/ksonnet/ksonnet"),
+	"ksonnet.beta.4": *deps.Parse("", "github.com/ksonnet/ksonnet-lib/ksonnet.beta.4"),
+	"prometheus":     *deps.Parse("", "github.com/prometheus/prometheus"),
+}