fix: accepting non-main.go files as well

Previous code was handling only main.go as the main build file, but
the main function can actually be in any file.

Now, if a specific file (*.go) is passed, that file will be checked
for the main function.

If a folder is passed, the package will be scanned for the main
function.

pipeline/build/build.go

@@ -45,7 +45,17 @@ func (Pipe) Run(ctx *context.Context) error {
 }
 
 func checkMain(ctx *context.Context, build config.Build) error {
-	var dir = strings.Replace(build.Main, "main.go", "", -1)
+	if strings.HasSuffix(build.Main, ".go") {
+		file, err := parser.ParseFile(token.NewFileSet(), build.Main, nil, 0)
+		if err != nil {
+			return errors.Wrapf(err, "failed to parse file: %s", build.Main)
+		}
+		if !hasMain(file) {
+			return fmt.Errorf("build for %s does not contain a main function", build.Binary)
+		}
+		return nil
+	}
+	var dir = build.Main
 	if dir == "" {
 		dir = "."
 	}
@@ -55,21 +65,27 @@ func checkMain(ctx *context.Context, build config.Build) error {
 	}
 	for _, pack := range packs {
 		for _, file := range pack.Files {
-			for _, decl := range file.Decls {
-				fn, ok := decl.(*ast.FuncDecl)
-				if !ok {
-					continue
-				}
-				log.Info(fn.Name.Name)
-				if fn.Name.Name == "main" && fn.Recv == nil {
-					return nil
-				}
+			if hasMain(file) {
+				return nil
 			}
 		}
 	}
 	return fmt.Errorf("build for %s does not contain a main function", build.Binary)
 }
 
+func hasMain(file *ast.File) bool {
+	for _, decl := range file.Decls {
+		fn, isFn := decl.(*ast.FuncDecl)
+		if !isFn {
+			continue
+		}
+		if fn.Name.Name == "main" && fn.Recv == nil {
+			return true
+		}
+	}
+	return false
+}
+
 func runPipeOnBuild(ctx *context.Context, build config.Build) error {
 	if err := runHook(build.Env, build.Hooks.Pre); err != nil {
 		return errors.Wrap(err, "pre hook failed")

pipeline/build/build_test.go

@@ -277,7 +277,7 @@ func TestRunPipeWithouMainFunc(t *testing.T) {
 	})
 	t.Run("not main.go", func(t *testing.T) {
 		ctx.Config.Builds[0].Main = "foo.go"
-		assert.EqualError(t, Pipe{}.Run(ctx), `failed to parse dir: foo.go: open foo.go: no such file or directory`)
+		assert.EqualError(t, Pipe{}.Run(ctx), `failed to parse file: foo.go: open foo.go: no such file or directory`)
 	})
 	t.Run("glob", func(t *testing.T) {
 		ctx.Config.Builds[0].Main = "."
@@ -289,23 +289,62 @@ func TestRunPipeWithouMainFunc(t *testing.T) {
 	})
 }
 
+func TestRunPipeWithMainFuncNotInMainGoFile(t *testing.T) {
+	folder, back := testlib.Mktmp(t)
+	defer back()
+	assert.NoError(t, ioutil.WriteFile(
+		filepath.Join(folder, "foo.go"),
+		[]byte("package main\nfunc main() {println(0)}"),
+		0644,
+	))
+	var config = config.Project{
+		Builds: []config.Build{
+			{
+				Binary: "foo",
+				Hooks:  config.Hooks{},
+				Goos: []string{
+					runtime.GOOS,
+				},
+				Goarch: []string{
+					runtime.GOARCH,
+				},
+			},
+		},
+	}
+	var ctx = context.New(config)
+	t.Run("empty", func(t *testing.T) {
+		ctx.Config.Builds[0].Main = ""
+		assert.NoError(t, Pipe{}.Run(ctx))
+	})
+	t.Run("foo.go", func(t *testing.T) {
+		ctx.Config.Builds[0].Main = "foo.go"
+		assert.NoError(t, Pipe{}.Run(ctx))
+	})
+	t.Run("glob", func(t *testing.T) {
+		ctx.Config.Builds[0].Main = "."
+		assert.NoError(t, Pipe{}.Run(ctx))
+	})
+}
+
 func exists(file string) bool {
 	_, err := os.Stat(file)
 	return !os.IsNotExist(err)
 }
 
 func writeMainWithoutMainFunc(t *testing.T, folder string) {
-	writeFile(t, folder, "package main\nconst a = 2\nfunc notMain() {println(0)}")
+	assert.NoError(t, ioutil.WriteFile(
+		filepath.Join(folder, "main.go"),
+		[]byte("package main\nconst a = 2\nfunc notMain() {println(0)}"),
+		0644,
+	))
 }
 
 func writeGoodMain(t *testing.T, folder string) {
-	writeFile(t, folder, "package main\nvar a = 1\nfunc main() {println(0)}")
-}
-
-func writeFile(t *testing.T, folder, content string) {
 	assert.NoError(t, ioutil.WriteFile(
-		filepath.Join(folder, "main.go"), []byte(content), 0644),
-	)
+		filepath.Join(folder, "main.go"),
+		[]byte("package main\nvar a = 1\nfunc main() {println(0)}"),
+		0644,
+	))
 }
 
 func assertContainsError(t *testing.T, err error, s string) {