language: add BaseLang (#1303)

In order to help folks extend Gazelle quicker and easier, provide a base
implementation of the language.Language interface where everything is
no-ops.

End users then can simply compose their downstream struct with this
to have a valid implementation to iterate upon.

internal/go_repository_tools_srcs.bzl

@@ -45,6 +45,7 @@ GO_REPOSITORY_TOOLS_SRCS = [
  Label("//label:BUILD.bazel"),
  Label("//label:label.go"),
  Label("//language:BUILD.bazel"),
+ Label("//language:base.go"),
  Label("//language/go:BUILD.bazel"),
  Label("//language/go:build_constraints.go"),
  Label("//language/go:config.go"),

internal/language/test_filegroup/BUILD.bazel

@@ -6,11 +6,7 @@ go_library(
  importpath = "github.com/bazelbuild/bazel-gazelle/internal/language/test_filegroup",
  visibility = ["//visibility:public"],
  deps = [
- "//config",
- "//label",
  "//language",
- "//repo",
- "//resolve",
  "//rule",
  ],
 )

internal/language/test_filegroup/lang.go

@@ -24,52 +24,28 @@ limitations under the License.
 package test_filegroup
 
 import (
- "flag"
  "path"
 
- "github.com/bazelbuild/bazel-gazelle/config"
- "github.com/bazelbuild/bazel-gazelle/label"
  "github.com/bazelbuild/bazel-gazelle/language"
- "github.com/bazelbuild/bazel-gazelle/repo"
- "github.com/bazelbuild/bazel-gazelle/resolve"
  "github.com/bazelbuild/bazel-gazelle/rule"
 )
 
 const testFilegroupName = "test_filegroup"
 
-type testFilegroupLang struct{}
+type testFilegroupLang struct {
+ language.BaseLang
+}
 
 func NewLanguage() language.Language {
  return &testFilegroupLang{}
 }
 
 func (*testFilegroupLang) Name() string { return testFilegroupName }
 
-func (*testFilegroupLang) RegisterFlags(fs *flag.FlagSet, cmd string, c *config.Config) {}
-
-func (*testFilegroupLang) CheckFlags(fs *flag.FlagSet, c *config.Config) error { return nil }
-
-func (*testFilegroupLang) KnownDirectives() []string { return nil }
-
-func (*testFilegroupLang) Configure(c *config.Config, rel string, f *rule.File) {}
-
 func (*testFilegroupLang) Kinds() map[string]rule.KindInfo {
  return kinds
 }
 
-func (*testFilegroupLang) Loads() []rule.LoadInfo { return nil }
-
-func (*testFilegroupLang) Fix(c *config.Config, f *rule.File) {}
-
-func (*testFilegroupLang) Imports(c *config.Config, r *rule.Rule, f *rule.File) []resolve.ImportSpec {
- return nil
-}
-
-func (*testFilegroupLang) Embeds(r *rule.Rule, from label.Label) []label.Label { return nil }
-
-func (*testFilegroupLang) Resolve(c *config.Config, ix *resolve.RuleIndex, rc *repo.RemoteCache, r *rule.Rule, imports interface{}, from label.Label) {
-}
-
 var kinds = map[string]rule.KindInfo{
  "filegroup": {
  NonEmptyAttrs: map[string]bool{"srcs": true, "deps": true},

language/BUILD.bazel

@@ -3,13 +3,15 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 go_library(
  name = "language",
  srcs = [
+ "base.go",
  "lang.go",
  "update.go",
  ],
  importpath = "github.com/bazelbuild/bazel-gazelle/language",
  visibility = ["//visibility:public"],
  deps = [
  "//config",
+ "//label",
  "//repo",
  "//resolve",
  "//rule",
@@ -21,6 +23,7 @@ filegroup(
  testonly = True,
  srcs = [
  "BUILD.bazel",
+ "base.go",
  "lang.go",
  "update.go",
  "//language/go:all_files",

language/base.go

@@ -0,0 +1,70 @@
+package language
+
+import (
+ "flag"
+
+ "github.com/bazelbuild/bazel-gazelle/config"
+ "github.com/bazelbuild/bazel-gazelle/label"
+ "github.com/bazelbuild/bazel-gazelle/repo"
+ "github.com/bazelbuild/bazel-gazelle/resolve"
+ "github.com/bazelbuild/bazel-gazelle/rule"
+)
+
+// BaseLang implements the minimum of language.Language interface.
+// This is not meant to be used directly by Gazelle, but to be used by
+// a downstream struct through composition. End users could use this to
+// write an extensions iteratively without having to implement every
+// functions in the interface right away.
+//
+// Example usage:
+//
+// type MyLang struct {
+// language.BaseLang
+// }
+//
+// func NewLanguage() language.Language {
+// return &MyLang{}
+// }
+//
+type BaseLang struct{}
+
+func (b *BaseLang) RegisterFlags(fs *flag.FlagSet, cmd string, c *config.Config) {}
+
+func (b *BaseLang) CheckFlags(fs *flag.FlagSet, c *config.Config) error {
+ return nil
+}
+
+func (b *BaseLang) KnownDirectives() []string {
+ return nil
+}
+
+func (b *BaseLang) Configure(c *config.Config, rel string, f *rule.File) {}
+
+func (b *BaseLang) Name() string {
+ return "BaseLang"
+}
+
+func (b *BaseLang) Imports(c *config.Config, r *rule.Rule, f *rule.File) []resolve.ImportSpec {
+ return nil
+}
+
+func (b *BaseLang) Embeds(r *rule.Rule, from label.Label) []label.Label {
+ return nil
+}
+
+func (b *BaseLang) Resolve(c *config.Config, ix *resolve.RuleIndex, rc *repo.RemoteCache, r *rule.Rule, imports interface{}, from label.Label) {
+}
+
+func (b *BaseLang) Kinds() map[string]rule.KindInfo {
+ return nil
+}
+
+func (b *BaseLang) Loads() []rule.LoadInfo {
+ return nil
+}
+
+func (b *BaseLang) GenerateRules(args GenerateArgs) GenerateResult {
+ return GenerateResult{}
+}
+
+func (b *BaseLang) Fix(c *config.Config, f *rule.File) {}