From d980c8532918a1908b47d2a5571432520e425102 Mon Sep 17 00:00:00 2001
From: Martin Fischer <martin@push-f.com>
Date: Sun, 30 Mar 2025 13:58:58 +0200
Subject: refactor: port to Go

---
 .gitignore         |   2 +-
 README.md          |   9 ++
 build.go           | 241 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 build.py           | 168 -------------------------------------
 fetch_and_build.sh |   2 +-
 go.mod             |  10 +++
 go.sum             |  17 ++++
 head.html          |  26 ------
 script.js          |  18 ++--
 style.css          |   6 +-
 template.html.tmpl |  53 ++++++++++++
 11 files changed, 346 insertions(+), 206 deletions(-)
 create mode 100644 build.go
 delete mode 100755 build.py
 create mode 100644 go.mod
 create mode 100644 go.sum
 delete mode 100644 head.html
 create mode 100644 template.html.tmpl

diff --git a/.gitignore b/.gitignore
index 23f3028..55b34c1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
 caniuse.rs/
 rust/
-target/
+out/
 lib_feats.txt
diff --git a/README.md b/README.md
index e69de29..64548ff 100644
--- a/README.md
+++ b/README.md
@@ -0,0 +1,9 @@
+# rust-features
+
+An autogenerated web page listing Rust features.
+
+Hosted under https://rust-features.push-f.com/.
+
+# Local development
+
+    go run build.go 
diff --git a/build.go b/build.go
new file mode 100644
index 0000000..9e91800
--- /dev/null
+++ b/build.go
@@ -0,0 +1,241 @@
+package main
+
+import (
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"html/template"
+	"maps"
+	"os"
+	"regexp"
+	"slices"
+	"strconv"
+	"strings"
+
+	"github.com/BurntSushi/toml"
+	log "github.com/sirupsen/logrus"
+)
+
+var codeRegex = regexp.MustCompile("`(.+?)`")
+
+//go:embed template.html.tmpl
+var templateText string
+
+//go:embed script.js
+var script []byte
+
+//go:embed style.css
+var style []byte
+
+func main() {
+	caniuseRepo := "caniuse.rs"
+	outDir := "out"
+
+	libFeaturesText, err := os.ReadFile("lib_feats.txt")
+	if err != nil {
+		log.Fatalf("error reading lib_feats.txt: %s", err)
+	}
+	libFeatureFlags := strings.Split(string(libFeaturesText), "\n")
+
+	versionInfos := make(map[string]VersionInfo)
+	versionsPath := fmt.Sprintf(caniuseRepo + "/data/versions.toml")
+	_, err = toml.DecodeFile(versionsPath, &versionInfos)
+	if err != nil {
+		log.Fatalf("error parsing %s: %s", versionsPath, err)
+	}
+
+	if len(versionInfos) == 0 {
+		log.Fatal("found no versions in versions.toml")
+	}
+
+	versions := make([]Version, 0)
+	sortedVersions := slices.SortedFunc(maps.Keys(versionInfos), compareVersion)
+	slices.Reverse(sortedVersions)
+
+	for _, name := range append([]string{"unstable"}, sortedVersions...) {
+		features := getFeatures(caniuseRepo, name)
+		if len(features) == 0 {
+			log.Infof("no features found for %s", name)
+		}
+		libFeatures := make([]Feature, 0)
+		nonLibFeatures := make([]Feature, 0)
+		for _, feature := range features {
+			if slices.Contains(libFeatureFlags, feature.Flag) || strings.Contains(feature.Title, " impl for ") {
+				libFeatures = append(libFeatures, feature)
+			} else {
+				nonLibFeatures = append(nonLibFeatures, feature)
+			}
+		}
+
+		version := Version{
+			Name:           name,
+			LibFeatures:    nilAsEmptyArray(slices.SortedFunc(slices.Values(libFeatures), compareFeature)),
+			NonLibFeatures: nilAsEmptyArray(slices.SortedFunc(slices.Values(nonLibFeatures), compareFeature)),
+		}
+		versionInfo := versionInfos[name]
+		if versionInfo.BlogPostPath != nil {
+			url := fmt.Sprintf("https://blog.rust-lang.org/%s", *versionInfo.BlogPostPath)
+			version.BlogPostURL = &url
+		}
+
+		versions = append(versions, version)
+	}
+
+	tmpl := template.New("template.html.tmpl").Funcs(template.FuncMap{
+		"formatBackticks": func(s string) template.HTML {
+			return template.HTML(codeRegex.ReplaceAllStringFunc(s, func(code string) string {
+				return fmt.Sprintf(
+					"<code>%s</code>",
+					template.HTMLEscapeString(codeRegex.FindStringSubmatch(code)[1]),
+				)
+			}))
+		},
+	})
+	tmpl, err = tmpl.Parse(templateText)
+
+	if err != nil {
+		log.Fatalf("error parsing template: %s", err)
+	}
+
+	err = os.MkdirAll(outDir, 0o755)
+	if err != nil {
+		log.Fatalf("error creating directory: %s", err)
+	}
+
+	outputFile, err := os.Create(outDir + "/index.html")
+	if err != nil {
+		log.Fatalf("error creating index.html: %s", err)
+	}
+	defer outputFile.Close()
+
+	err = tmpl.Execute(outputFile,
+		map[string]any{
+			"Versions": versions,
+		},
+	)
+	if err != nil {
+		log.Fatalf("error executing template: %s", err)
+	}
+
+	outputFile, err = os.Create(outDir + "/data.json")
+	if err != nil {
+		log.Fatalf("error creating data.json: %s", err)
+	}
+	defer outputFile.Close()
+
+	encoder := json.NewEncoder(outputFile)
+	err = encoder.Encode(versions)
+	if err != nil {
+		log.Fatalf("error encoding JSON: %s", err)
+	}
+
+	err = os.WriteFile(outDir+"/script.js", script, 0o644)
+	if err != nil {
+		log.Fatalf("error creating script.js: %s", err)
+	}
+
+	err = os.WriteFile(outDir+"/style.css", style, 0o644)
+	if err != nil {
+		log.Fatalf("error creating style.css: %s", err)
+	}
+}
+
+type Version struct {
+	Name           string    `json:"name"`
+	BlogPostURL    *string   `json:"-"`
+	LibFeatures    []Feature `json:"lib"`
+	NonLibFeatures []Feature `json:"non_lib"`
+}
+
+// Version info from "caniuse.rs/data/versions.toml".
+type VersionInfo struct {
+	BlogPostPath *string `toml:"blog_post_path"`
+}
+
+// Data from a .toml file in "caniuse.rs/data/{version}/".
+type Feature struct {
+	Title             string   `toml:"title" json:"title"`
+	Flag              string   `toml:"flag" json:"flag"`
+	TrackingIssueId   *uint    `toml:"tracking_issue_id" json:"-"`
+	ImplPrId          *uint    `toml:"impl_pr_id" json:"-"`
+	StabilizationPrId *uint    `toml:"stabilization_pr_id" json:"-"`
+	Aliases           []string `toml:"aliases" json:"aliases"`
+	Items             []string `toml:"items" json:"items"`
+	URL               string   `json:"url"`
+}
+
+func getFeatures(caniuseRepo string, version string) map[string]Feature {
+	dirPath := caniuseRepo + "/data/" + version
+	entries, err := os.ReadDir(dirPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+		log.Fatal(err)
+	}
+
+	features := make(map[string]Feature)
+
+	for _, entry := range entries {
+		var feature Feature
+		_, err := toml.DecodeFile(dirPath+"/"+entry.Name(), &feature)
+		if err != nil {
+			log.Fatalf("Error parsing %s: %s\n", dirPath+entry.Name(), err)
+		}
+		if feature.TrackingIssueId != nil {
+			feature.URL = fmt.Sprintf("https://github.com/rust-lang/rust/issues/%d", *feature.TrackingIssueId)
+		} else if feature.ImplPrId != nil {
+			feature.URL = fmt.Sprintf("https://github.com/rust-lang/rust/pull/%d", *feature.ImplPrId)
+		} else if feature.StabilizationPrId != nil {
+			feature.URL = fmt.Sprintf("https://github.com/rust-lang/rust/pull/%d", *feature.StabilizationPrId)
+		}
+		feature.Title = strings.TrimPrefix(feature.Title, "the ")
+		feature.Title = strings.Replace(feature.Title, "implementation", "impl", 1)
+		var key string
+		if feature.Flag == "" {
+			key = entry.Name()
+		} else {
+			key = feature.Flag
+		}
+		_, exists := features[key]
+		if exists {
+			// caniuse.rs sometimes intentionally has several .toml files
+			// for the same feature flag (with different titles).
+			// In this case we only want to display the feature once.
+			feature.Title = feature.Flag
+		}
+		features[key] = feature
+	}
+	return features
+}
+
+func compareFeature(a, b Feature) int {
+	aTitle := strings.ToLower(strings.TrimLeft(a.Title, "`"))
+	bTitle := strings.ToLower(strings.TrimLeft(b.Title, "`"))
+	if aTitle > bTitle {
+		return 1
+	} else if aTitle < bTitle {
+		return -1
+	}
+	return 0
+}
+
+func compareVersion(a, b string) int {
+	aParts := strings.Split(a, ".")
+	bParts := strings.Split(b, ".")
+
+	aMajor, _ := strconv.Atoi(aParts[0])
+	bMajor, _ := strconv.Atoi(bParts[0])
+	if aMajor != bMajor {
+		return aMajor - bMajor
+	}
+
+	aMinor, _ := strconv.Atoi(aParts[1])
+	bMinor, _ := strconv.Atoi(bParts[1])
+	return aMinor - bMinor
+}
+
+// workaround for https://github.com/golang/go/issues/37711
+func nilAsEmptyArray[T any](slice []T) []T {
+	return append([]T{}, slice...)
+}
diff --git a/build.py b/build.py
deleted file mode 100755
index d0f7fba..0000000
--- a/build.py
+++ /dev/null
@@ -1,168 +0,0 @@
-#!/usr/bin/env python3
-import html
-import json
-import os
-import re
-import shutil
-import tomllib
-
-
-def get_features(dirname):
-    feature_data = {}
-    for feature in sorted(os.listdir('caniuse.rs/data/' + dirname)):
-        with open('caniuse.rs/data/' + dirname + '/' + feature, 'rb') as f:
-            name = feature.split('.')[0]
-            feature_data[name] = tomllib.load(f)
-
-    # new dict because we want to deduplicate features
-    features = {}
-
-    # caniuse.rs sometimes has several .toml files for one feature flag e.g.
-    # For the const_io feature flag it has 6 .toml files, all with the same
-    # tracking_issue_id but different titles.
-    #
-    # That makes sense for a search-centric application.  Not so much for a
-    # static-site generator since showing the same link 6 times is confusing.
-    for feat, data in feature_data.items():
-        key = data['flag'] if 'flag' in data else feat
-
-        url = None
-        if 'tracking_issue_id' in data:
-            url = 'https://github.com/rust-lang/rust/issues/{}'.format(
-                data['tracking_issue_id']
-            )
-        elif 'impl_pr_id' in data:
-            url = 'https://github.com/rust-lang/rust/pull/{}'.format(data['impl_pr_id'])
-        elif 'stabilization_pr_id' in data:
-            url = 'https://github.com/rust-lang/rust/pull/{}'.format(
-                data['stabilization_pr_id']
-            )
-        data['url'] = url
-        data['filename'] = feat
-
-        if data['title'].startswith('the '):
-            data['title'] = data['title'][len('the ') :]
-        data['title'] = data['title'].replace('implementation', 'impl')
-
-        if key in features:
-            data['title'] = data['flag'].replace('_', ' ')
-
-        if key in features and features[key]['url'] != url:
-            print(
-                'different urls for feature {}:\n* {}: {}\n* {}: {}'.format(
-                    key,
-                    data['filename'],
-                    data['url'],
-                    features[key]['filename'],
-                    features[key]['url'],
-                )
-            )
-
-        features[key] = data
-
-    features = dict(
-        sorted(features.items(), key=lambda t: t[1]['title'].replace('`', '').lower())
-    )
-
-    lib_features = {}
-    non_lib_features = {}
-
-    for key, data in features.items():
-        if ('flag' in data and data['flag'] in library_flags) or 'impl for' in data[
-            'title'
-        ]:
-            lib_features[key] = data
-        else:
-            non_lib_features[key] = data
-
-    return dict(lib_features=lib_features, non_lib_features=non_lib_features)
-
-
-with open('lib_feats.txt') as f:
-    library_flags = set([l.strip() for l in f])
-
-with open('caniuse.rs/data/versions.toml', 'rb') as f:
-    versions = tomllib.load(f)
-
-for version, data in versions.items():
-    try:
-        data['features'] = get_features(version)
-    except FileNotFoundError:
-        pass
-
-versions = dict(reversed(list(versions.items())))
-
-unstable_features = get_features('unstable')
-
-
-os.makedirs('target', exist_ok=True)
-shutil.copy('style.css', 'target')
-shutil.copy('script.js', 'target')
-
-with open('target/data.json', 'w') as f:
-    data = dict(unstable=dict(features=unstable_features), **versions)
-    json.dump(data, f)
-
-
-def write_features(f, id, features):
-    if features['non_lib_features']:
-        write_feature_list(f, id + '-non-lib', features['non_lib_features'])
-    if features['lib_features']:
-        f.write('<h3 id="{}">library</h3>'.format(id + '-lib'))
-        write_feature_list(f, id + '-lib', features['lib_features'])
-
-
-def write_feature_list(f, id, features):
-    f.write('<ul id={}-list'.format(id))
-    if len(features) > 5:
-        f.write(' class=columns')
-    f.write('>')
-    for feat, data in features.items():
-        f.write('<li><a')
-        if 'flag' in data:
-            f.write(' title="{}"'.format(data['flag']))
-        url = data['url']
-        if url:
-            f.write(f' href="{url}"')
-        f.write('>')
-        title = html.escape(data['title'])
-        title = re.sub('`(.+?)`', lambda m: '<code>{}</code>'.format(m.group(1)), title)
-        f.write(title)
-        f.write('</a></li>')
-    f.write('</ul>')
-
-
-with open('target/index.html', 'w') as f:
-    with open('head.html') as h:
-        f.write(h.read())
-
-    f.write('<h2 id=unstable>Unstable features</h2>')
-    write_features(f, 'unstable', unstable_features)
-
-    after_beta = False
-
-    for version, data in versions.items():
-        f.write('<div id={0} class=release>'.format(version))
-        f.write('<h2>{}'.format(version))
-        channel = data.get('channel')
-        if after_beta:
-            channel = 'stable'
-            after_beta = False
-        if channel:
-            if channel == 'nightly':
-                channel = 'stabilized'
-            elif channel == 'beta':
-                after_beta = True
-            f.write(' [{}]'.format(channel))
-        f.write('</h2>')
-
-        if 'blog_post_path' in data:
-            f.write(
-                '<a class=release-notes href="https://blog.rust-lang.org/{}">{}</a>'.format(
-                    data['blog_post_path'], 'release notes'
-                )
-            )
-        f.write('</div>')
-
-        if 'features' in data:
-            write_features(f, version, data['features'])
diff --git a/fetch_and_build.sh b/fetch_and_build.sh
index 760b03d..ba1c91c 100755
--- a/fetch_and_build.sh
+++ b/fetch_and_build.sh
@@ -2,4 +2,4 @@
 (cd rust; git checkout master; git pull --ff-only)
 ./find.sh | grep -oP '(?<=feature = ")([^"]+)' > lib_feats.txt
 rm -r build/
-./build.py
+go run build.go
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..37a793b
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,10 @@
+module push-f.com/rust-features
+
+go 1.23.5
+
+require (
+	github.com/BurntSushi/toml v1.5.0
+	github.com/sirupsen/logrus v1.9.3
+)
+
+require golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..4f5a5ea
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,17 @@
+github.com/BurntSushi/toml v1.5.0 h1:W5quZX/G/csjUnuI8SUYlsHs9M38FC7znL0lIO+DvMg=
+github.com/BurntSushi/toml v1.5.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
+github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 h1:0A+M6Uqn+Eje4kHMK80dtF3JCXC4ykBgQG4Fe06QRhQ=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/head.html b/head.html
deleted file mode 100644
index 2caa40b..0000000
--- a/head.html
+++ /dev/null
@@ -1,26 +0,0 @@
-<!doctype html>
-<html>
-<head>
-<meta charset=utf-8>
-<title>Rust features</title>
-<link rel="stylesheet" href="style.css" />
-<meta name="viewport" content="width=device-width, initial-scale=1">
-</head>
-<body>
-
-<div class=header>
-<div class=left><h1>Rust features</h1></div>
-<input id=search autocomplete=off tabindex=4>
-<noscript>
-With JavaScript you get a search box here.
-<style>
-#search { display: none; }
-</style>
-</noscript>
-<script src=script.js></script>
-<div class=right></div>
-</div>
-<div style="clear: both"></div>
-
-page generated by <a tabindex=1 target=_blank href="https://push-f.com/">push-f</a>
-         from the <a tabindex=2 target=_blank href="https://github.com/jplatte/caniuse.rs">caniuse.rs dataset</a>
diff --git a/script.js b/script.js
index a631288..0e2491e 100644
--- a/script.js
+++ b/script.js
@@ -6,32 +6,32 @@
 	input.focus();
 	input.addEventListener('input', (e) => {
 		const query = e.target.value.toLowerCase();
-		for (const [key, data] of Object.entries(versions)) {
-			const heading = document.getElementById(key);
+		for (const version of versions) {
+			const heading = document.getElementById(version.name);
 
-			if (data.features == undefined) {
+			if (version.lib.length == 0 && version.non_lib.length == 0) {
 				heading.hidden = query.length != 0;
 				continue;
 			}
-			const nonLibResults = search(data.features.non_lib_features, query);
-			const libResults = search(data.features.lib_features, query);
+			const nonLibResults = search(version.non_lib, query);
+			const libResults = search(version.lib, query);
 
 			const totalResultCount = nonLibResults.length + libResults.length;
 
 			// so that release notes don't get in the way when <Tab>ing through results
 			document.body.classList.toggle('hide-release-notes', totalResultCount == 0);
 
-			let list = document.getElementById(key + '-non-lib-list');
+			let list = document.getElementById(version.name + '-non-lib-list');
 			if (list) {
 				list.replaceChildren(...renderList(nonLibResults).children);
 				list.hidden = nonLibResults.length == 0;
 			}
 
-			list = document.getElementById(key + '-lib-list');
+			list = document.getElementById(version.name + '-lib-list');
 			if (list) {
 				list.replaceChildren(...renderList(libResults).children);
 				list.hidden = libResults.length == 0;
-				document.getElementById(key + '-lib').hidden = libResults.length == 0;
+				document.getElementById(version.name + '-lib-heading').hidden = libResults.length == 0;
 			}
 
 			heading.hidden = totalResultCount == 0;
@@ -40,7 +40,7 @@
 })();
 
 function search(features, query) {
-	return Object.values(features).filter((feat) => {
+	return features.filter((feat) => {
 		if (feat.title.toLowerCase().replaceAll('`', '').includes(query)) {
 			return true;
 		}
diff --git a/style.css b/style.css
index 8c8559f..6ad3fd2 100644
--- a/style.css
+++ b/style.css
@@ -2,7 +2,11 @@ body {
 	font-family: sans;
 }
 
-.columns {
+a {
+    text-decoration: none;
+}
+
+ul {
 	columns: 300px;
 }
 
diff --git a/template.html.tmpl b/template.html.tmpl
new file mode 100644
index 0000000..d993725
--- /dev/null
+++ b/template.html.tmpl
@@ -0,0 +1,53 @@
+<!doctype html>
+<html>
+<head>
+<meta charset=utf-8>
+<title>Rust features</title>
+<link rel="stylesheet" href="style.css" />
+<meta name="viewport" content="width=device-width, initial-scale=1">
+</head>
+<body>
+
+<div class=header>
+<div class=left><h1>Rust features</h1></div>
+<input id=search autocomplete=off tabindex=4>
+<noscript>
+With JavaScript you get a search box here.
+<style>
+#search { display: none; }
+</style>
+</noscript>
+<script src=script.js></script>
+<div class=right></div>
+</div>
+<div style="clear: both"></div>
+
+page generated by <a tabindex=1 target=_blank href="https://push-f.com/">push-f</a>
+         from the <a tabindex=2 target=_blank href="https://github.com/jplatte/caniuse.rs">caniuse.rs dataset</a>
+
+{{range .Versions}}
+    <div class=release>
+        <h2 id="{{.Name}}">{{.Name}}</h2>
+        {{with .BlogPostURL}}
+           <a href="{{.}}" class=release-notes>release notes</a>
+        {{end}}
+    </div>
+    {{if .NonLibFeatures}}
+        <ul id="{{.Name}}-non-lib-list">
+            {{- range .NonLibFeatures}}
+                <li>{{template "feature" .}}</li>
+            {{- end}}
+        </ul>
+    {{end}}
+    {{if .LibFeatures}}
+        <h3 id="{{.Name}}-lib-heading">library</h3>
+        <ul id="{{.Name}}-lib-list">
+            {{- range .LibFeatures}}
+                <li>{{template "feature" .}}</li>
+            {{- end}}
+        </ul>
+    {{end}}
+{{end}}
+{{define "feature" -}}
+    <a {{with .URL}}href="{{.}}"{{end}} {{with .Flag}}title="{{.}}"{{end}}>{{.Title | formatBackticks}}</a>
+{{- end}}
-- 
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