Feature documentation (#7814)

# Objective

- Fixes #1800, fixes #6984
- Alternative to #7196
- Ensure feature list is always up to date and that all are documented
- Help discovery of features

## Solution

- Use a template to update the cargo feature list
- Use the comment just above the feature declaration as the description
- Add the checks to CI
- Add the features to the base crate doc

.github/bors.toml

@@ -9,6 +9,7 @@ status = [
     "run-examples-on-wasm",
     "check-doc",
     "check-missing-examples-in-docs",
+    "check-missing-features-in-docs",
     # "check-unused-dependencies",
     "ci",
     "check-compiles",

.github/workflows/ci-comment-failures.yml

@@ -117,7 +117,65 @@ jobs:
                 owner: context.repo.owner,
                 repo: context.repo.repo,
                 issue_number: issue_number,
-                body: 'You added a new example but didn\'t update the readme. Please run `cargo run -p build-example-pages -- update` to update it, and commit the file change.'
+                body: 'You added a new example but didn\'t update the readme. Please run `cargo run -p build-templated-pages -- update examples` to update it, and commit the file change.'
+              });
+            }
+
+  missing-features:
+    runs-on: ubuntu-latest
+    if: >
+      github.event.workflow_run.event == 'pull_request' &&
+      github.event.workflow_run.conclusion == 'failure'
+    steps:
+      - name: 'Download artifact'
+        id: find-artifact
+        uses: actions/github-script@v6
+        with:
+          result-encoding: string
+          script: |
+            var artifacts = await github.rest.actions.listWorkflowRunArtifacts({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               run_id: ${{github.event.workflow_run.id }},
+            });
+            var matchArtifacts = artifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "missing-features"
+            });
+            if (matchArtifacts.length == 0) { return "false" }
+            var matchArtifact = matchArtifacts[0];
+            var download = await github.rest.actions.downloadArtifact({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               artifact_id: matchArtifact.id,
+               archive_format: 'zip',
+            });
+            var fs = require('fs');
+            fs.writeFileSync('${{github.workspace}}/missing-features.zip', Buffer.from(download.data));
+            return "true"
+      - run: unzip missing-features.zip
+        if: ${{ steps.find-artifact.outputs.result == 'true' }}
+      - name: 'Comment on PR'
+        if: ${{ steps.find-artifact.outputs.result == 'true' }}
+        uses: actions/github-script@v6
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            var fs = require('fs');
+            var issue_number = Number(fs.readFileSync('./NR'));
+            if (fs.existsSync('./missing-features')) {
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: issue_number,
+                body: 'You added a new feature but didn\'t add a description for it. Please update the root Cargo.toml file.'
+              });
+            }
+            if (fs.existsSync('./missing-update')) {
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: issue_number,
+                body: 'You added a new feature but didn\'t update the readme. Please run `cargo run -p build-templated-pages -- update features` to update it, and commit the file change.'
               });
             }
 

.github/workflows/ci.yml

@@ -257,14 +257,14 @@ jobs:
       - uses: actions/checkout@v3
       - name: check for missing metadata
         id: missing-metadata
-        run: cargo run -p build-example-pages -- check-missing
+        run: cargo run -p build-templated-pages -- check-missing examples
       - name: check for missing update
         id: missing-update
-        run: cargo run -p build-example-pages -- update
+        run: cargo run -p build-templated-pages -- update examples
       - name: Check for modified files
         run: |
           echo "if this step fails, run the following command and commit the changed file on your PR."
-          echo " > cargo run -p build-example-pages -- update"
+          echo " > cargo run -p build-templated-pages -- update examples"
           git diff --quiet HEAD --
       - name: Save PR number
         if: ${{ failure() && github.event_name == 'pull_request' }}
@@ -283,6 +283,39 @@ jobs:
           name: missing-examples
           path: missing-examples/
 
+  check-missing-features-in-docs:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v3
+      - name: check for missing features
+        id: missing-features
+        run: cargo run -p build-templated-pages -- check-missing features
+      - name: check for missing update
+        id: missing-update
+        run: cargo run -p build-templated-pages -- update features
+      - name: Check for modified files
+        run: |
+          echo "if this step fails, run the following command and commit the changed file on your PR."
+          echo " > cargo run -p build-templated-pages -- update features"
+          git diff --quiet HEAD --
+      - name: Save PR number
+        if: ${{ failure() && github.event_name == 'pull_request' }}
+        run: |
+          mkdir -p ./missing-features
+          echo ${{ github.event.number }} > ./missing-features/NR
+      - name: log failed task - missing features
+        if: ${{ failure() && github.event_name == 'pull_request' && steps.missing-features.conclusion == 'failure' }}
+        run: touch ./missing-features/missing-features
+      - name: log failed task - missing update
+        if: ${{ failure() && github.event_name == 'pull_request' && steps.missing-update.conclusion == 'failure' }}
+        run: touch ./missing-features/missing-update
+      - uses: actions/upload-artifact@v2
+        if: ${{ failure() && github.event_name == 'pull_request' }}
+        with:
+          name: missing-features
+          path: missing-features/
+
   check-unused-dependencies:
     runs-on: ubuntu-latest
     timeout-minutes: 30

Cargo.toml

@@ -22,7 +22,7 @@ members = [
   "crates/*",
   "examples/mobile",
   "tools/ci",
-  "tools/build-example-pages",
+  "tools/build-templated-pages",
   "tools/build-wasm-example",
   "errors",
 ]
@@ -56,62 +56,136 @@ default = [
 # Force dynamic linking, which improves iterative compile times
 dynamic_linking = ["bevy_dylib", "bevy_internal/dynamic_linking"]
 
-# Optional bevy crates
+# Provides animation functionality
 bevy_animation = ["bevy_internal/bevy_animation"]
+
+# Provides asset functionality
 bevy_asset = ["bevy_internal/bevy_asset"]
+
+# Provides audio functionality
 bevy_audio = ["bevy_internal/bevy_audio"]
+
+# Provides cameras and other basic render pipeline features
 bevy_core_pipeline = ["bevy_internal/bevy_core_pipeline"]
+
+# Plugin for dynamic loading (using [libloading](https://crates.io/crates/libloading))
 bevy_dynamic_plugin = ["bevy_internal/bevy_dynamic_plugin"]
+
+# Adds gamepad support
 bevy_gilrs = ["bevy_internal/bevy_gilrs"]
+
+# [glTF](https://www.khronos.org/gltf/) support
 bevy_gltf = ["bevy_internal/bevy_gltf"]
+
+# Adds PBR rendering
 bevy_pbr = ["bevy_internal/bevy_pbr"]
+
+# Provides rendering functionality
 bevy_render = ["bevy_internal/bevy_render"]
+
+# Provides scene functionality
 bevy_scene = ["bevy_internal/bevy_scene"]
+
+# Provides sprite functionality
 bevy_sprite = ["bevy_internal/bevy_sprite"]
+
+# Provides text functionality
 bevy_text = ["bevy_internal/bevy_text"]
+
+# A custom ECS-driven UI framework
 bevy_ui = ["bevy_internal/bevy_ui"]
+
+# winit window and input backend
 bevy_winit = ["bevy_internal/bevy_winit"]
 
-# Tracing features
+# Tracing support, saving a file in Chrome Tracing format
 trace_chrome = ["trace", "bevy_internal/trace_chrome"]
+
+# Tracing support, exposing a port for Tracy
 trace_tracy = ["trace", "bevy_internal/trace_tracy"]
+
+# Tracing support
 trace = ["bevy_internal/trace"]
+
+# Save a trace of all wgpu calls
 wgpu_trace = ["bevy_internal/wgpu_trace"]
 
-# Image format support for texture loading (PNG and HDR are enabled by default)
+# EXR image format support
 exr = ["bevy_internal/exr"]
+
+# HDR image format support
 hdr = ["bevy_internal/hdr"]
+
+# PNG image format support
 png = ["bevy_internal/png"]
+
+# TGA image format support
 tga = ["bevy_internal/tga"]
+
+# JPEG image format support
 jpeg = ["bevy_internal/jpeg"]
+
+# BMP image format support
 bmp = ["bevy_internal/bmp"]
+
+# Basis Universal compressed texture support
 basis-universal = ["bevy_internal/basis-universal"]
+
+# DDS compressed texture support
 dds = ["bevy_internal/dds"]
+
+# KTX2 compressed texture support
 ktx2 = ["bevy_internal/ktx2"]
-# For ktx2 supercompression
+
+# For KTX2 supercompression
 zlib = ["bevy_internal/zlib"]
+
+# For KTX2 supercompression
 zstd = ["bevy_internal/zstd"]
 
-# Audio format support (vorbis is enabled by default)
+# FLAC audio format support
 flac = ["bevy_internal/flac"]
+
+# MP3 audio format support
 mp3 = ["bevy_internal/mp3"]
+
+# OGG/VORBIS audio format support
 vorbis = ["bevy_internal/vorbis"]
+
+# WAV audio format support
 wav = ["bevy_internal/wav"]
+
+# AAC audio format support (through symphonia)
 symphonia-aac = ["bevy_internal/symphonia-aac"]
+
+# AAC, FLAC, MP3, MP4, OGG/VORBIS, and WAV audio formats support (through symphonia)
 symphonia-all = ["bevy_internal/symphonia-all"]
+
+# FLAC audio format support (through symphonia)
 symphonia-flac = ["bevy_internal/symphonia-flac"]
+
+# MP4 audio format support (through symphonia)
 symphonia-isomp4 = ["bevy_internal/symphonia-isomp4"]
+
+# MP3 audio format support (through symphonia)
 symphonia-mp3 = ["bevy_internal/symphonia-mp3"]
+
+# OGG/VORBIS audio format support (through symphonia)
 symphonia-vorbis = ["bevy_internal/symphonia-vorbis"]
+
+# WAV audio format support (through symphonia)
 symphonia-wav = ["bevy_internal/symphonia-wav"]
 
 # Enable watching file system for asset hot reload
 filesystem_watcher = ["bevy_internal/filesystem_watcher"]
 
+# Enable serialization support through serde
 serialize = ["bevy_internal/serialize"]
 
-# Display server protocol support (X11 is enabled by default)
+# Wayland display server support
 wayland = ["bevy_internal/wayland"]
+
+# X11 display server support
 x11 = ["bevy_internal/x11"]
 
 # Enable rendering of font glyphs using subpixel accuracy
@@ -124,16 +198,15 @@ bevy_ci_testing = ["bevy_internal/bevy_ci_testing"]
 debug_asset_server = ["bevy_internal/debug_asset_server"]
 
 # Enable animation support, and glTF animation loading
-animation = ["bevy_internal/animation"]
+animation = ["bevy_internal/animation", "bevy_animation"]
 
-# Enable using a shared stdlib for cxx on Android.
+# Enable using a shared stdlib for cxx on Android
 android_shared_stdcxx = ["bevy_internal/android_shared_stdcxx"]
 
-# Enable detailed trace event logging.
-# These trace events are expensive even when off, thus they require compile time opt-in.
+# Enable detailed trace event logging. These trace events are expensive even when off, thus they require compile time opt-in
 detailed_trace = ["bevy_internal/detailed_trace"]
 
-# Include tonemapping LUT KTX2 files.
+# Include tonemapping Look Up Tables KTX2 files
 tonemapping_luts = ["bevy_internal/tonemapping_luts"]
 
 [dependencies]
@@ -1267,7 +1340,7 @@ category = "Scene"
 wasm = false
 
 # Shaders
-[[package.metadata.category]]
+[[package.metadata.example_category]]
 name = "Shaders"
 description = """
 These examples demonstrate how to implement different shaders in user code.
@@ -1399,7 +1472,7 @@ category = "Shaders"
 wasm = false
 
 # Stress tests
-[[package.metadata.category]]
+[[package.metadata.example_category]]
 name = "Stress Tests"
 description = """
 These examples are used to test the performance and stability of various parts of the engine in an isolated way.

docs-template/features.md.tpl

@@ -0,0 +1,21 @@
+<!-- MD041 - This file will be included in docs and should not start with a top header -->
+<!-- markdownlint-disable-file MD041 -->
+
+## Cargo Features
+
+Bevy exposes many features to customise the engine. Enabling them add functionalities but often come at the cost of longer compilation times and extra dependencies.
+
+### Default Features
+
+The default feature set enables most of the expected features of a game engine, like rendering in both 2D and 3D, asset loading, audio and UI. To help reduce compilation time, consider disabling default features and enabling only those you need.
+
+|feature name|description|
+|-|-|
+{% for feature in features %}{% if feature.is_default %}|{{ feature.name }}|{{ feature.description }}|
+{% endif %}{% endfor %}
+### Optional Features
+
+|feature name|description|
+|-|-|
+{% for feature in features %}{% if feature.is_default == False %}|{{ feature.name }}|{{ feature.description }}|
+{% endif %}{% endfor %}

docs/cargo_features.md

@@ -1,53 +1,70 @@
-# Cargo Features
+<!-- MD041 - This file will be included in docs and should not start with a top header -->
+<!-- markdownlint-disable-file MD041 -->
 
-## Default Features
+## Cargo Features
+
+Bevy exposes many features to customise the engine. Enabling them add functionalities but often come at the cost of longer compilation times and extra dependencies.
+
+### Default Features
+
+The default feature set enables most of the expected features of a game engine, like rendering in both 2D and 3D, asset loading, audio and UI. To help reduce compilation time, consider disabling default features and enabling only those you need.
 
 |feature name|description|
 |-|-|
-|animation|Animation support and glTF animation loading.|
-|bevy_asset|Provides asset functionality for Bevy Engine.|
-|bevy_audio|Audio support. Support for all audio formats depends on this.|
-|bevy_gilrs|Adds gamepad support.|
-|bevy_gltf|[glTF](https://www.khronos.org/gltf/) support.|
-|bevy_scene|Provides scene functionality for Bevy Engine.|
-|bevy_winit|GUI support.|
-|render|The render pipeline and all render related plugins.|
-|png|PNG picture format support.|
-|hdr|[HDR](https://en.wikipedia.org/wiki/High_dynamic_range) support.|
-|vorbis|Ogg Vorbis audio format support.|
-|x11|Make GUI applications use X11 protocol. You could enable wayland feature to override this.|
-|filesystem_watcher|Enable watching the file system for asset hot reload|
+|android_shared_stdcxx|Enable using a shared stdlib for cxx on Android|
+|animation|Enable animation support, and glTF animation loading|
+|bevy_animation|Provides animation functionality|
+|bevy_asset|Provides asset functionality|
+|bevy_audio|Provides audio functionality|
+|bevy_core_pipeline|Provides cameras and other basic render pipeline features|
+|bevy_gilrs|Adds gamepad support|
+|bevy_gltf|[glTF](https://www.khronos.org/gltf/) support|
+|bevy_pbr|Adds PBR rendering|
+|bevy_render|Provides rendering functionality|
+|bevy_scene|Provides scene functionality|
+|bevy_sprite|Provides sprite functionality|
+|bevy_text|Provides text functionality|
+|bevy_ui|A custom ECS-driven UI framework|
+|bevy_winit|winit window and input backend|
+|filesystem_watcher|Enable watching file system for asset hot reload|
+|hdr|HDR image format support|
+|ktx2|KTX2 compressed texture support|
+|png|PNG image format support|
+|tonemapping_luts|Include tonemapping Look Up Tables KTX2 files|
+|vorbis|OGG/VORBIS audio format support|
+|x11|X11 display server support|
+|zstd|For KTX2 supercompression|
 
-## Optional Features
+### Optional Features
 
 |feature name|description|
 |-|-|
-|bevy_dynamic_plugin|Plugin for dynamic loading (using [libloading](https://crates.io/crates/libloading)).|
-|dynamic_linking|Forces bevy to be dynamically linked, which improves iterative compile times.|
-|trace|Enables system tracing.|
-|trace_chrome|Enables [tracing-chrome](https://github.com/thoren-d/tracing-chrome) as bevy_log output. This allows you to visualize system execution.|
-|trace_tracy|Enables [Tracy](https://github.com/wolfpld/tracy) as bevy_log output. This allows `Tracy` to connect to and capture profiling data as well as visualize system execution in real-time, present statistics about system execution times, and more.|
-|wgpu_trace|For tracing wgpu.|
-|dds|DDS picture format support.|
-|ktx2|KTX2 picture format support.|
-|zlib|KTX2 Zlib supercompression support.|
-|zstd|KTX2 Zstandard supercompression support.|
-|basis-universal|Basis Universal picture format support and, if the `ktx2` feature is enabled, also KTX2 UASTC picture format transcoding support.|
-|tga|TGA picture format support.|
-|jpeg|JPEG picture format support.|
-|bmp|BMP picture format support.|
-|flac|FLAC audio format support. It's included in bevy_audio feature.|
-|mp3|MP3 audio format support.|
-|wav|WAV audio format support.|
-|symphonia-aac|AAC audio format support by Symphonia. For more details, see `symphonia-all`.|
-|symphonia-all|AAC, FLAC, MP4, MP3, Vorbis, and WAV support by Symphonia. Add support for parsing multiple file formats using a single crate instead of compiling different crates. The other non-`symphonia` features are disabled when its corresponding `symphonia` feature is enabled. [Link to `symphonia` documentation](https://docs.rs/symphonia/latest/symphonia/). More information about this topic can be found [here](https://github.com/bevyengine/bevy/pull/6388#discussion_r1009622883) |
-|symphonia-flac|FLAC audio format support by Symphonia. For more details, see `symphonia-all`.|
-|symphonia-isomp4|MP4 audio format support by Symphonia. For more details, see `symphonia-all`.|
-|symphonia-mp3|MP3 audio format support by Symphonia. For more details, see `symphonia-all`.|
-|symphonia-vorbis|Vorbis audio format support by Symphonia. For more details, see `symphonia-all`.|
-|symphonia-wav|WAV audio format support by Symphonia. For more details, see `symphonia-all`.|
-|serialize|Enables serialization of `bevy_input` types.|
-|wayland|Enable this to use Wayland display server protocol other than X11.|
-|subpixel_glyph_atlas|Enable this to cache glyphs using subpixel accuracy. This increases texture memory usage as each position requires a separate sprite in the glyph atlas, but provide more accurate character spacing.|
-|bevy_ci_testing|Used for running examples in CI.|
-|debug_asset_server|Enabling this turns on "hot reloading" of built in assets, such as shaders.|
+|basis-universal|Basis Universal compressed texture support|
+|bevy_ci_testing|Enable systems that allow for automated testing on CI|
+|bevy_dynamic_plugin|Plugin for dynamic loading (using [libloading](https://crates.io/crates/libloading))|
+|bmp|BMP image format support|
+|dds|DDS compressed texture support|
+|debug_asset_server|Enable the "debug asset server" for hot reloading internal assets|
+|detailed_trace|Enable detailed trace event logging. These trace events are expensive even when off, thus they require compile time opt-in|
+|dynamic_linking|Force dynamic linking, which improves iterative compile times|
+|exr|EXR image format support|
+|flac|FLAC audio format support|
+|jpeg|JPEG image format support|
+|mp3|MP3 audio format support|
+|serialize|Enable serialization support through serde|
+|subpixel_glyph_atlas|Enable rendering of font glyphs using subpixel accuracy|
+|symphonia-aac|AAC audio format support (through symphonia)|
+|symphonia-all|AAC, FLAC, MP3, MP4, OGG/VORBIS, and WAV audio formats support (through symphonia)|
+|symphonia-flac|FLAC audio format support (through symphonia)|
+|symphonia-isomp4|MP4 audio format support (through symphonia)|
+|symphonia-mp3|MP3 audio format support (through symphonia)|
+|symphonia-vorbis|OGG/VORBIS audio format support (through symphonia)|
+|symphonia-wav|WAV audio format support (through symphonia)|
+|tga|TGA image format support|
+|trace|Tracing support|
+|trace_chrome|Tracing support, saving a file in Chrome Tracing format|
+|trace_tracy|Tracing support, exposing a port for Tracy|
+|wav|WAV audio format support|
+|wayland|Wayland display server support|
+|wgpu_trace|Save a trace of all wgpu calls|
+|zlib|For KTX2 supercompression|

src/lib.rs

@@ -10,6 +10,7 @@
 //! community](https://bevyengine.org/community/) if you have any questions or ideas!
 //!
 //! ## Example
+//!
 //! Here is a simple "Hello World" Bevy app:
 //! ```
 //! use bevy::prelude::*;
@@ -28,7 +29,8 @@
 //! Don't let the simplicity of the example above fool you. Bevy is a [fully featured game engine](https://bevyengine.org)
 //! and it gets more powerful every day!
 //!
-//! ### This Crate
+//! ## This Crate
+//!
 //! The `bevy` crate is just a container crate that makes it easier to consume Bevy subcrates.
 //! The defaults provide a "full" engine experience, but you can easily enable / disable features
 //! in your project's `Cargo.toml` to meet your specific needs. See Bevy's `Cargo.toml` for a full
@@ -37,7 +39,7 @@
 //! If you prefer, you can also consume the individual bevy crates directly.
 //! Each module in the root of this crate, except for the prelude, can be found on crates.io
 //! with `bevy_` appended to the front, e.g. `app` -> [`bevy_app`](https://docs.rs/bevy_app/*/bevy_app/).
-
+#![doc = include_str!("../docs/cargo_features.md")]
 #![doc(
     html_logo_url = "https://bevyengine.org/assets/icon.png",
     html_favicon_url = "https://bevyengine.org/assets/icon.png"

tools/build-templated-pages/Cargo.toml

@@ -1,8 +1,8 @@
 [package]
-name = "build-example-pages"
+name = "build-templated-pages"
 version = "0.9.0"
 edition = "2021"
-description = "handle examples in Bevy"
+description = "handle templated pages in Bevy repository"
 publish = false
 license = "MIT OR Apache-2.0"
 

tools/build-templated-pages/src/examples.rs

@@ -1,60 +1,10 @@
 use std::{cmp::Ordering, collections::HashMap, fs::File};
 
-use bitflags::bitflags;
 use serde::Serialize;
 use tera::{Context, Tera};
 use toml_edit::Document;
 
-bitflags! {
-    struct Command: u32 {
-        const CHECK_MISSING = 0b00000001;
-        const UPDATE = 0b00000010;
-    }
-}
-
-fn main() {
-    let what_to_run = match std::env::args().nth(1).as_deref() {
-        Some("check-missing") => Command::CHECK_MISSING,
-        Some("update") => Command::UPDATE,
-        _ => Command::all(),
-    };
-
-    let examples = parse_examples(what_to_run.contains(Command::CHECK_MISSING));
-
-    if what_to_run.contains(Command::UPDATE) {
-        let categories = parse_categories();
-        let examples_by_category: HashMap<String, Category> = examples
-            .into_iter()
-            .fold(HashMap::<String, Vec<Example>>::new(), |mut v, ex| {
-                v.entry(ex.category.clone()).or_default().push(ex);
-                v
-            })
-            .into_iter()
-            .map(|(key, mut examples)| {
-                examples.sort();
-                let description = categories.get(&key).cloned();
-                (
-                    key,
-                    Category {
-                        description,
-                        examples,
-                    },
-                )
-            })
-            .collect();
-
-        let mut context = Context::new();
-        context.insert("all_examples", &examples_by_category);
-        Tera::new("examples/*.md.tpl")
-            .expect("error parsing template")
-            .render_to(
-                "README.md.tpl",
-                &context,
-                File::create("examples/README.md").expect("error creating file"),
-            )
-            .expect("error rendering template");
-    }
-}
+use crate::Command;
 
 #[derive(Debug, Serialize, PartialEq, Eq)]
 struct Category {
@@ -138,7 +88,7 @@ fn parse_categories() -> HashMap<String, String> {
         .unwrap()
         .get("metadata")
         .as_ref()
-        .unwrap()["category"]
+        .unwrap()["example_category"]
         .clone()
         .as_array_of_tables()
         .unwrap()
@@ -151,3 +101,41 @@ fn parse_categories() -> HashMap<String, String> {
         })
         .collect()
 }
+
+pub(crate) fn check(what_to_run: Command) {
+    let examples = parse_examples(what_to_run.contains(Command::CHECK_MISSING));
+
+    if what_to_run.contains(Command::UPDATE) {
+        let categories = parse_categories();
+        let examples_by_category: HashMap<String, Category> = examples
+            .into_iter()
+            .fold(HashMap::<String, Vec<Example>>::new(), |mut v, ex| {
+                v.entry(ex.category.clone()).or_default().push(ex);
+                v
+            })
+            .into_iter()
+            .map(|(key, mut examples)| {
+                examples.sort();
+                let description = categories.get(&key).cloned();
+                (
+                    key,
+                    Category {
+                        description,
+                        examples,
+                    },
+                )
+            })
+            .collect();
+
+        let mut context = Context::new();
+        context.insert("all_examples", &examples_by_category);
+        Tera::new("docs-template/*.md.tpl")
+            .expect("error parsing template")
+            .render_to(
+                "EXAMPLE_README.md.tpl",
+                &context,
+                File::create("examples/README.md").expect("error creating file"),
+            )
+            .expect("error rendering template");
+    }
+}

tools/build-templated-pages/src/features.rs

@@ -0,0 +1,110 @@
+use std::{cmp::Ordering, fs::File};
+
+use serde::Serialize;
+use tera::{Context, Tera};
+use toml_edit::Document;
+
+use crate::Command;
+
+#[derive(Debug, Serialize, PartialEq, Eq)]
+struct Feature {
+    name: String,
+    description: String,
+    is_default: bool,
+}
+
+impl Ord for Feature {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.name.cmp(&other.name)
+    }
+}
+
+impl PartialOrd for Feature {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+fn parse_features(panic_on_missing: bool) -> Vec<Feature> {
+    let manifest_file = std::fs::read_to_string("Cargo.toml").unwrap();
+    let manifest = manifest_file.parse::<Document>().unwrap();
+
+    let features = manifest["features"].as_table().unwrap();
+    let default: Vec<_> = features
+        .get("default")
+        .unwrap()
+        .as_array()
+        .unwrap()
+        .iter()
+        .flat_map(|v| {
+            std::iter::once(v.as_str().unwrap().to_string()).chain(
+                features
+                    .get(v.as_str().unwrap())
+                    .unwrap()
+                    .as_array()
+                    .unwrap()
+                    .iter()
+                    .map(|v| v.as_str().unwrap().to_string()),
+            )
+        })
+        .collect();
+
+    features
+        .get_values()
+        .iter()
+        .flat_map(|(key, _)| {
+            let key = key[0];
+
+            if key == "default" {
+                None
+            } else {
+                let name = key
+                    .as_repr()
+                    .unwrap()
+                    .as_raw()
+                    .as_str()
+                    .unwrap()
+                    .to_string();
+                if let Some(description) = key.decor().prefix() {
+                    let description = description.as_str().unwrap().to_string();
+                    if !description.starts_with("\n# ") || !description.ends_with('\n') {
+                        panic!("Missing description for feature {name}");
+                    }
+                    let description = description
+                        .strip_prefix("\n# ")
+                        .unwrap()
+                        .strip_suffix('\n')
+                        .unwrap()
+                        .to_string();
+                    Some(Feature {
+                        is_default: default.contains(&name),
+                        name,
+                        description,
+                    })
+                } else if panic_on_missing {
+                    panic!("Missing description for feature {name}");
+                } else {
+                    None
+                }
+            }
+        })
+        .collect()
+}
+
+pub(crate) fn check(what_to_run: Command) {
+    let mut features = parse_features(what_to_run.contains(Command::CHECK_MISSING));
+    features.sort();
+
+    if what_to_run.contains(Command::UPDATE) {
+        let mut context = Context::new();
+        context.insert("features", &features);
+        Tera::new("docs-template/*.md.tpl")
+            .expect("error parsing template")
+            .render_to(
+                "features.md.tpl",
+                &context,
+                File::create("docs/cargo_features.md").expect("error creating file"),
+            )
+            .expect("error rendering template");
+    }
+}

tools/build-templated-pages/src/main.rs

@@ -0,0 +1,39 @@
+use bitflags::bitflags;
+
+mod examples;
+mod features;
+
+bitflags! {
+    struct Command: u32 {
+        const CHECK_MISSING = 0b00000001;
+        const UPDATE = 0b00000010;
+    }
+}
+
+bitflags! {
+    struct Target: u32 {
+        const EXAMPLES = 0b00000001;
+        const FEATURES = 0b00000010;
+    }
+}
+
+fn main() {
+    let what_to_run = match std::env::args().nth(1).as_deref() {
+        Some("check-missing") => Command::CHECK_MISSING,
+        Some("update") => Command::UPDATE,
+        _ => Command::all(),
+    };
+
+    let target = match std::env::args().nth(2).as_deref() {
+        Some("examples") => Target::EXAMPLES,
+        Some("features") => Target::FEATURES,
+        _ => Target::all(),
+    };
+
+    if target.contains(Target::EXAMPLES) {
+        examples::check(what_to_run);
+    }
+    if target.contains(Target::FEATURES) {
+        features::check(what_to_run);
+    }
+}