crate-features: Added a tool to summarise unstable Rust feature use

See #13

Signed-off-by: SlyMarbo <[email protected]>

tools/crate-features/BUILD.bazel

@@ -0,0 +1,27 @@
+# Copyright 2022 The Firefly Authors.
+#
+# Use of this source code is governed by a BSD 3-clause
+# license that can be found in the LICENSE file.
+
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("//bazel/gofmt:gofmt.bzl", "gofmt")
+
+go_library(
+    name = "crate-features_lib",
+    srcs = [
+        "main.go",
+    ],
+    importpath = "firefly-os.dev/tools/crate-features",
+    visibility = ["//visibility:private"],
+)
+
+gofmt(
+    name = "gofmt",
+    embed = [":crate-features_lib"],
+)
+
+go_binary(
+    name = "crate-features",
+    embed = [":crate-features_lib"],
+    visibility = ["//visibility:public"],
+)

tools/crate-features/main.go

@@ -0,0 +1,155 @@
+// Copyright 2022 The Firefly Authors.
+//
+// Use of this source code is governed by a BSD 3-clause
+// license that can be found in the LICENSE file.
+
+// Command crate-features analyses the Rust crates in the
+// repository for unstable features, printing a summary.
+//
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io/fs"
+	"log"
+	"os"
+	"path"
+	"sort"
+	"strings"
+	"text/tabwriter"
+)
+
+// Features parses the given file, returning the set
+// of unstable Rust features the crate requires.
+//
+func Features(fsys fs.FS, name string) ([]string, error) {
+	f, err := fsys.Open(name)
+	if err != nil {
+		return nil, err
+	}
+
+	defer f.Close()
+
+	found := make(map[string]bool)
+	s := bufio.NewScanner(f)
+	for s.Scan() {
+		const (
+			featurePrefix = "#![feature("
+			featureSuffix = ")]"
+		)
+
+		line := s.Text()
+		if !strings.HasPrefix(line, featurePrefix) {
+			continue
+		}
+
+		features := strings.TrimPrefix(line, featurePrefix)
+
+		// Drop any trailing line comment.
+		if i := strings.Index(features, "//"); i > 0 {
+			features = strings.TrimSpace(features[:i])
+		}
+
+		if !strings.HasSuffix(features, featureSuffix) {
+			log.Printf("WARN:  %s: malformed feature inner attribute line: %q", name, line)
+			continue
+		}
+
+		features = strings.TrimSuffix(features, featureSuffix)
+		for _, feature := range strings.Split(features, ",") {
+			found[strings.TrimSpace(feature)] = true
+		}
+	}
+
+	if err := s.Err(); err != nil {
+		return nil, err
+	}
+
+	if len(found) == 0 {
+		return nil, nil
+	}
+
+	features := make([]string, 0, len(found))
+	for feature := range found {
+		features = append(features, feature)
+	}
+
+	sort.Strings(features)
+
+	return features, nil
+}
+
+func init() {
+	log.SetFlags(0)
+	log.SetOutput(os.Stderr)
+	log.SetPrefix("")
+}
+
+func main() {
+	// If we're being run with `bazel run`, we're in
+	// a semi-random build directory, and need to move
+	// to the workspace root directory.
+	//
+	workspace := os.Getenv("BUILD_WORKSPACE_DIRECTORY")
+	if workspace != "" {
+		err := os.Chdir(workspace)
+		if err != nil {
+			log.Printf("Failed to change directory to %q: %v", workspace, err)
+		}
+	}
+
+	features := make(map[string][]string)
+	fsys := os.DirFS(".")
+	err := fs.WalkDir(fsys, ".", func(name string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if d.IsDir() {
+			return nil
+		}
+
+		if path.Base(name) != "lib.rs" {
+			return nil
+		}
+
+		found, err := Features(fsys, name)
+		if err != nil {
+			return err
+		}
+
+		crate := path.Dir(name)
+		if path.Base(crate) == "src" {
+			crate = path.Dir(crate)
+		}
+
+		for _, feature := range found {
+			features[feature] = append(features[feature], crate)
+		}
+
+		return nil
+	})
+
+	if err != nil {
+		log.Fatalf("Failed to scan repository: %v", err)
+	}
+
+	sorted := make([]string, 0, len(features))
+	for feature, crates := range features {
+		sorted = append(sorted, feature)
+		sort.Strings(crates)
+	}
+
+	sort.Strings(sorted)
+
+	w := tabwriter.NewWriter(os.Stdout, 0, 8, 1, ' ', 0)
+	for _, feature := range sorted {
+		fmt.Fprintf(w, "%s\t%s\n", feature, strings.Join(features[feature], ", "))
+	}
+
+	err = w.Flush()
+	if err != nil {
+		log.Fatalf("Failed to print summary: %v", err)
+	}
+}