Rewrite verify_readmes.sh script in Go

Makefile

@@ -43,6 +43,9 @@ $(TOOLS)/crosslink: PACKAGE=go.opentelemetry.io/build-tools/crosslink
 SEMCONVKIT = $(TOOLS)/semconvkit
 $(TOOLS)/semconvkit: PACKAGE=go.opentelemetry.io/otel/$(TOOLS_MOD_DIR)/semconvkit
 
+VERIFYREADMES = $(TOOLS)/verifyreadmes
+$(TOOLS)/verifyreadmes: PACKAGE=go.opentelemetry.io/otel/$(TOOLS_MOD_DIR)/verifyreadmes
+
 GOLANGCI_LINT = $(TOOLS)/golangci-lint
 $(TOOLS)/golangci-lint: PACKAGE=github.com/golangci/golangci-lint/v2/cmd/golangci-lint
 
@@ -68,7 +71,7 @@ GOVULNCHECK = $(TOOLS)/govulncheck
 $(TOOLS)/govulncheck: PACKAGE=golang.org/x/vuln/cmd/govulncheck
 
 .PHONY: tools
-tools: $(CROSSLINK) $(GOLANGCI_LINT) $(MISSPELL) $(GOCOVMERGE) $(STRINGER) $(PORTO) $(SEMCONVGEN) $(MULTIMOD) $(SEMCONVKIT) $(GOTMPL) $(GORELEASE)
+tools: $(CROSSLINK) $(GOLANGCI_LINT) $(MISSPELL) $(GOCOVMERGE) $(STRINGER) $(PORTO) $(SEMCONVGEN) $(VERIFYREADMES) $(MULTIMOD) $(SEMCONVKIT) $(GOTMPL) $(GORELEASE)
 
 # Virtualized python tools via docker
 
@@ -322,5 +325,5 @@ lint-markdown:
 	docker run --rm -u $(DOCKER_USER) -v "$(CURDIR):$(WORKDIR)" $(MARKDOWNIMAGE) -c $(WORKDIR)/.markdownlint.yaml $(WORKDIR)/**/*.md
 
 .PHONY: verify-readmes
-verify-readmes:
-	./verify_readmes.sh
+verify-readmes: $(VERIFYREADMES)
+	$(VERIFYREADMES)

internal/tools/verifyreadmes/main.go

@@ -0,0 +1,80 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package verifyreadmes is used to verify that all go modules in the repository
+// have a README.md file.
+package main
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// excludedDirs is a list of directories to exclude from the README check if the full path contains any of these strings.
+var excludedDirs = []string{
+	"internal",
+	"test",
+	"example",
+	"/.",
+}
+
+const readmeFilename = "README.md"
+
+// verifyReadme is a [os.WalkFunc] that checks if a README.md exists in the same directory as the go.mod file.
+func verifyReadme(path string, info os.FileInfo, err error) error {
+	if err != nil {
+		return err
+	}
+
+	if !info.Mode().IsRegular() || info.Name() != "go.mod" {
+		return nil
+
+	}
+
+	for _, dir := range excludedDirs {
+		if strings.Contains(path, dir) {
+			return nil
+		}
+	}
+
+
+	// Check that a README.md exists in the same directory as the go.mod file.
+	readme := filepath.Join(filepath.Dir(path), readmeFilename)
+	_, err = os.Stat(readme)
+	if os.IsNotExist(err) {
+		err = fmt.Errorf("couldn't find %s for %q", readmeFilename, filepath.Dir(path))
+	}
+
+	return err
+}
+
+func main() {
+	root, err := os.Getwd()
+	if len(os.Args) == 2 {
+		root, err = filepath.Abs(os.Args[1])
+	}
+
+	if err != nil {
+		fmt.Println("Error: ", err)
+		os.Exit(1)
+	}
+
+	fmt.Println("Verifying READMEs in", root)
+
+	var errs []string
+	filepath.Walk(root, func(path string, info fs.FileInfo, err error) error {
+		if err := verifyReadme(path, info, err); err != nil {
+			errs = append(errs, err.Error())
+		}
+		return nil // continue walking
+	})
+
+	if len(errs) > 0 {
+		fmt.Println("Some readme files couldn't be found.")
+		fmt.Println(strings.Join(errs, "\n"))
+		os.Exit(1)
+	}
+}