language/go: several naming convention fixes plus auto-detection (#842)

* For external dependency resolution, if we don't know what naming
  convention the external repository uses (for example, because
  there's no known repository), we'll now use
  goDefaultLibraryNamingConvention. This avoids assuming that
  repositories with build files fetched with http_archive have been
  updated.
* In migrateNamingConvention, print a warning and avoid renaming if
  there's already a target with the new name.
* Library, test, and alias actuals are now generated based on import
  path instead of package name.
* Added unknownNamingConvention, a new zero value.
* Added detectNamingConvention. It reads the root build file and build
  files in subdirectories one level deep to infer the naming
  convention used if one is not specified in the root build
  file. Defaults to importNamingConvention.
* Delete empty go_library rules in directories with go_binary.
* Fixed tests.

For #5

cmd/gazelle/diff_test.go

@@ -55,7 +55,7 @@ func TestDiffExisting(t *testing.T) {
  # gazelle:prefix example.com/hello
  
 +go_library(
-+    name = "go_default_library",
++    name = "hello",
 +    srcs = ["hello.go"],
 +    importpath = "example.com/hello",
 +    visibility = ["//visibility:public"],
@@ -91,7 +91,7 @@ func TestDiffNew(t *testing.T) {
 +load("@io_bazel_rules_go//go:def.bzl", "go_library")
 +
 +go_library(
-+    name = "go_default_library",
++    name = "hello",
 +    srcs = ["hello.go"],
 +    importpath = "example.com/hello",
 +    visibility = ["//visibility:public"],
@@ -138,7 +138,7 @@ func TestDiffReadWriteDir(t *testing.T) {
  # gazelle:prefix example.com/hello
 +
 +go_library(
-+    name = "go_default_library",
++    name = "hello",
 +    srcs = ["hello.go"],
 +    importpath = "example.com/hello",
 +    visibility = ["//visibility:public"],

cmd/gazelle/fix_test.go

@@ -257,13 +257,13 @@ load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
 
 go_binary(
     name = "hello",
-    embed = [":go_default_library"],
+    embed = [":repo_lib"],
     pure = "on",
     visibility = ["//visibility:public"],
 )
 
 go_library(
-    name = "go_default_library",
+    name = "repo_lib",
     srcs = ["hello.go"],
     importpath = "example.com/repo",
     visibility = ["//visibility:private"],
@@ -291,15 +291,15 @@ load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
 # src build file
 
 go_library(
-    name = "go_default_library",
+    name = "repo_lib",
     srcs = ["hello.go"],
     importpath = "example.com/repo",
     visibility = ["//visibility:private"],
 )
 
 go_binary(
     name = "repo",
-    embed = [":go_default_library"],
+    embed = [":repo_lib"],
     visibility = ["//visibility:public"],
 )
 `,
@@ -324,13 +324,13 @@ load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
 
 go_binary(
     name = "hello",
-    embed = [":go_default_library"],
+    embed = [":repo_lib"],
     pure = "on",
     visibility = ["//visibility:public"],
 )
 
 go_library(
-    name = "go_default_library",
+    name = "repo_lib",
     srcs = ["hello.go"],
     importpath = "example.com/repo",
     visibility = ["//visibility:private"],

cmd/gazelle/integration_test.go

@@ -524,24 +524,24 @@ import _ "golang.org/x/baz"
 			Content: `load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["a.go"],
     importpath = "example.com/foo",
     visibility = ["//visibility:public"],
-    deps = ["//vendor/golang.org/x/bar:go_default_library"],
+    deps = ["//vendor/golang.org/x/bar"],
 )
 `,
 		}, {
 			Path: "vendor/golang.org/x/bar/" + config.DefaultValidBuildFileNames[0],
 			Content: `load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "bar",
     srcs = ["bar.go"],
     importmap = "example.com/foo/vendor/golang.org/x/bar",
     importpath = "golang.org/x/bar",
     visibility = ["//visibility:public"],
-    deps = ["//vendor/golang.org/x/baz:go_default_library"],
+    deps = ["//vendor/golang.org/x/baz"],
 )
 `,
 		},
@@ -898,11 +898,11 @@ import (
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "bar",
     srcs = ["bar.go"],
     importpath = "bar",
     visibility = ["//visibility:public"],
-    deps = ["//foo:go_default_library"],
+    deps = ["//foo"],
 )
 `,
 	}})
@@ -1007,7 +1007,7 @@ import _ "example.com/foo"
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["foo.go"],
     importmap = "example.com/repo/sub/vendor/example.com/foo",
     importpath = "example.com/foo",
@@ -1020,11 +1020,11 @@ go_library(
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "bar",
     srcs = ["bar.go"],
     importpath = "example.com/repo/sub/bar",
     visibility = ["//visibility:public"],
-    deps = ["//sub/vendor/example.com/foo:go_default_library"],
+    deps = ["//sub/vendor/example.com/foo"],
 )
 `,
 		},
@@ -1140,11 +1140,11 @@ import _ "example.com/bar"
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["foo.go"],
     importpath = "example.com/foo",
     visibility = ["//visibility:public"],
-    deps = ["@custom_repo//:go_default_library"],
+    deps = ["@custom_repo//:bar"],
 )
 `,
 		},
@@ -1179,6 +1179,7 @@ import _ "example.com/bar"
 	extDir := filepath.Join(dir, "ext")
 	args := []string{
 		"-go_prefix=example.com/foo",
+		"-go_naming_convention=import_alias",
 		"-mode=fix",
 		"-repo_root=" + extDir,
 		"-repo_config=" + filepath.Join(dir, "main", "WORKSPACE"),
@@ -1194,11 +1195,17 @@ import _ "example.com/bar"
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["foo.go"],
     importpath = "example.com/foo",
     visibility = ["//visibility:public"],
-    deps = ["@custom_repo//:go_default_library"],
+    deps = ["@custom_repo//:bar"],
+)
+
+alias(
+    name = "go_default_library",
+    actual = ":foo",
+    visibility = ["//visibility:public"],
 )
 `,
 		},
@@ -2246,7 +2253,7 @@ import _ "example.com/bar"
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "bar",
     srcs = ["bar.go"],
     importpath = "example.com/bar",
     visibility = ["//visibility:public"],
@@ -2272,11 +2279,11 @@ go_library(
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["foo.go"],
     importpath = "example.com/repo/foo",
     visibility = ["//visibility:public"],
-    deps = ["//vendor/example.com/bar:go_default_library"],
+    deps = ["//vendor/example.com/bar"],
 )
 `,
 	}})
@@ -2311,7 +2318,7 @@ import (
 
 # this should be ignored because -index=false
 go_library(
-    name = "go_default_library",
+    name = "baz",
     srcs = ["baz.go"],
     importpath = "example.com/dep/baz",
     visibility = ["//visibility:public"],
@@ -2342,11 +2349,11 @@ go_library(
 			Content: `load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["foo.go"],
     importpath = "example.com/repo/foo",
     visibility = ["//visibility:public"],
-    deps = ["//vendor/example.com/dep/baz:go_default_library"],
+    deps = ["//vendor/example.com/dep/baz"],
 )
 `,
 		},
@@ -2394,13 +2401,13 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 # gazelle:prefix example.com/sub
 
 go_library(
-    name = "go_default_library",
+    name = "sub",
     srcs = ["sub.go"],
     importpath = "example.com/sub",
     visibility = ["//visibility:public"],
     deps = [
-        "//sub/missing:go_default_library",
-        "//vendor/example.com/external:go_default_library",
+        "//sub/missing",
+        "//vendor/example.com/external",
     ],
 )
 `,
@@ -2564,8 +2571,11 @@ func TestMapKind(t *testing.T) {
 		{
 			Path: "WORKSPACE",
 		}, {
-			Path:    "BUILD.bazel",
-			Content: "# gazelle:prefix example.com/mapkind",
+			Path: "BUILD.bazel",
+			Content: `
+# gazelle:prefix example.com/mapkind
+# gazelle:go_naming_convention go_default_library
+`,
 		}, {
 			Path:    "root_lib.go",
 			Content: `package mapkind`,
@@ -2654,6 +2664,7 @@ go_library(
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 # gazelle:prefix example.com/mapkind
+# gazelle:go_naming_convention go_default_library
 
 go_library(
     name = "go_default_library",
@@ -2820,7 +2831,7 @@ func TestMinimalModuleCompatibilityAliases(t *testing.T) {
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     srcs = ["foo.go"],
     importpath = "example.com/foo/v2",
     importpath_aliases = ["example.com/foo"],
@@ -2833,7 +2844,7 @@ go_library(
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
-    name = "go_default_library",
+    name = "bar",
     srcs = ["bar.go"],
     importpath = "example.com/foo/v2/bar",
     importpath_aliases = ["example.com/foo/bar"],
@@ -2880,7 +2891,7 @@ go_repository(
 load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
-    name = "go_default_library",
+    name = "version",
     srcs = ["version.go"],
     importpath = "example.com/m/internal/version",
     visibility = [
@@ -2890,9 +2901,9 @@ go_library(
 )
 
 go_test(
-    name = "go_default_test",
+    name = "version_test",
     srcs = ["version_test.go"],
-    embed = [":go_default_library"],
+    embed = [":version"],
 )
 `,
 	}})
@@ -3101,7 +3112,7 @@ go_proto_library(
 )
 
 go_library(
-    name = "go_default_library",
+    name = "foo",
     embed = [":foo_go_proto"],
     importpath = "example.com/foo",
     visibility = ["//visibility:public"],
@@ -3159,7 +3170,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 # gazelle:lang
 
 go_library(
-    name = "go_default_library",
+    name = "bar",
     srcs = ["bar.go"],
     importpath = "",
     visibility = ["//visibility:public"],
@@ -3173,7 +3184,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 # gazelle:lang go,proto
 
 go_library(
-    name = "go_default_library",
+    name = "baz",
     srcs = ["baz.go"],
     importpath = "",
     visibility = ["//visibility:public"],
@@ -3241,11 +3252,58 @@ proto_library(
 )
 
 go_library(
-    name = "go_default_library",
+    name = "proto",
     srcs = ["foo.pb.go"],
     importpath = "example.com/proto",
     visibility = ["//visibility:public"],
 )`,
 		},
 	})
 }
+
+func TestGoMainLibraryRemoved(t *testing.T) {
+	files := []testtools.FileSpec{
+		{
+			Path: "WORKSPACE",
+		},
+		{
+			Path: "BUILD.bazel",
+			Content: `
+# gazelle:prefix example.com
+# gazelle:go_naming_convention import
+`,
+		},
+		{
+			Path: "cmd/foo/BUILD.bazel",
+			Content: `load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+		name = "foo_lib",
+		srcs = ["foo.go"],
+		importpath = "example.com/cmd/foo",
+		visibility = ["//visibility:private"],
+)
+
+go_binary(
+		name = "foo",
+		embed = [":foo_lib"],
+		visibility = ["//visibility:public"],
+)
+`,
+		},
+	}
+	dir, cleanup := testtools.CreateFiles(t, files)
+	defer cleanup()
+
+	args := []string{"update"}
+	if err := runGazelle(dir, args); err != nil {
+		t.Fatal(err)
+	}
+
+	testtools.CheckFiles(t, dir, []testtools.FileSpec{
+		{
+			Path:    "cmd/foo/BUILD.bazel",
+			Content: "",
+		},
+	})
+}