Add the maincheck linter that ensures all the main functions are decl…

…ared

in a file that is called main.go

GitOrigin-RevId: 6d554550b9b9edd19bda3c7ab9a5d16e28a8d017

nogo.bzl

@@ -1,5 +1,6 @@
 nogo_deps = [
-    "@com_github_scionproto_scion//tools/lint/log:log",
+    "@com_github_scionproto_scion//tools/lint/log:go_default_library",
+    "@com_github_scionproto_scion//tools/lint/maincheck:go_default_library",
     "@com_github_oncilla_gochecks//logcheck:go_default_library",
     "@com_github_oncilla_gochecks//serrorscheck:go_default_library",
     "@org_golang_x_tools//go/analysis/passes/asmdecl:go_default_library",

nogo.json

@@ -99,5 +99,11 @@
     "exclude_files": {
       "com_github_grpc_ecosystem_go_grpc_middleware/retry": ""
     }
+  },
+  "maincheck": {
+    "exclude_files": {
+        "/com_github_deepmap_oapi_codegen/": "",
+        "/com_github_golang_mock/mockgen": ""
+    }
   }
-}
+}

scion/cmd/scion/BUILD.bazel

@@ -5,9 +5,9 @@ go_library(
     name = "go_default_library",
     srcs = [
         "address.go",
+        "main.go",
         "observability.go",
         "ping.go",
-        "scion.go",
         "showpaths.go",
         "traceroute.go",
     ],

tools/lint/log/BUILD.bazel

@@ -1,11 +1,9 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
-
-#gazelle:ignore gazelle would add a go_library block which we don't need here.
+load("//lint:go.bzl", "go_library")
 
 go_library(
-    name = "log",
+    name = "go_default_library",
     srcs = ["log.go"],
-    importpath = "lint",
+    importpath = "github.com/scionproto/scion/tools/lint/log",
     visibility = ["//visibility:public"],
     deps = [
         "@org_golang_x_tools//go/analysis:go_default_library",

tools/lint/maincheck/BUILD.bazel

@@ -0,0 +1,9 @@
+load("//lint:go.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["maincheck.go"],
+    importpath = "github.com/scionproto/scion/tools/lint/maincheck",
+    visibility = ["//visibility:public"],
+    deps = ["@org_golang_x_tools//go/analysis:go_default_library"],
+)

tools/lint/maincheck/maincheck.go

@@ -0,0 +1,72 @@
+// Copyright 2022 Anapaya Systems
+//
+// 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 maincheck
+
+import (
+	"go/ast"
+	"path/filepath"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var permitted = []string{
+	"main.go",
+	"testmain.go",                    // bazel uses this for unit and integration tests.
+	"go_default_mock_gomock_prog.go", // bazel uses this for mock generation.
+}
+
+// Analyzer contains an analyzer that makes sure that go target is always a
+// func literal that calls defer log.HandlePanic as first statement.
+var Analyzer = &analysis.Analyzer{
+	Name:             "maincheck",
+	Doc:              "Check that main function is located in a main.go file",
+	Run:              run,
+	RunDespiteErrors: true,
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	for _, file := range pass.Files {
+		// If this is not a main package, we can exit early.
+		if file.Name.Name != "main" {
+			return nil, nil
+		}
+
+		for _, dec := range file.Decls {
+			fun, ok := dec.(*ast.FuncDecl)
+			if !ok {
+				continue
+			}
+			if fun.Name.Name != "main" {
+				continue
+			}
+			base := filepath.Base(pass.Fset.File(file.Name.NamePos).Name())
+			found := func() bool {
+				for _, p := range permitted {
+					if base == p {
+						return true
+					}
+				}
+				return false
+			}()
+
+			if !found {
+				pass.Reportf(fun.Pos(),
+					"main function must be located in a file called main.go instead of %s", base,
+				)
+			}
+		}
+	}
+	return nil, nil
+}

tools/pathdb_dump/BUILD.bazel

@@ -3,7 +3,7 @@ load("//:scion.bzl", "scion_go_binary")
 
 go_library(
     name = "go_default_library",
-    srcs = ["pathdb_dump.go"],
+    srcs = ["main.go"],
     importpath = "github.com/scionproto/scion/tools/pathdb_dump",
     visibility = ["//visibility:private"],
     deps = [

tools/pktgen/cmd/pktgen/BUILD.bazel

@@ -5,7 +5,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "config.go",
-        "pktgen.go",
+        "main.go",
     ],
     importpath = "github.com/scionproto/scion/tools/pktgen/cmd/pktgen",
     visibility = ["//visibility:private"],
@@ -40,7 +40,7 @@ go_test(
     srcs = [
         "config_test.go",
         "export_test.go",
-        "pktgen_test.go",
+        "main_test.go",
     ],
     data = glob(["testdata/**"]),
     embed = [":go_default_library"],

tools/udpproxy/BUILD.bazel

@@ -3,7 +3,7 @@ load("@io_bazel_rules_docker//go:image.bzl", "go_image")
 
 go_library(
     name = "go_default_library",
-    srcs = ["udpproxy.go"],
+    srcs = ["main.go"],
     importpath = "github.com/scionproto/scion/tools/udpproxy",
     visibility = ["//visibility:private"],
     deps = [