Create mdbook-tera-backend renderer (#80)

Create renderer

Co-authored-by: Martin Geisler <martin@geisler.net>

Cargo.toml

@@ -1,4 +1,4 @@
 [workspace]
-members = ["i18n-helpers"]
+members = ["i18n-helpers", "mdbook-tera-backend"]
 default-members = ["i18n-helpers"]
 resolver = "2"

README.md

@@ -8,8 +8,10 @@
 This repository contains the following crates that provide extensions and
 infrastructure for [mdbook](https://github.com/rust-lang/mdBook/):
 
-- [mdbook-i18n-helpers](i18n-helpers/README.md): Gettext translation support for
-  [mdbook](https://github.com/rust-lang/mdBook/)
+- [mdbook-i18n-helpers](./i18n-helpers/README.md): Gettext translation support
+  for [mdbook](https://github.com/rust-lang/mdBook/)
+- [mdbook-tera-backend](./mdbook-tera-backend/README.md): Tera templates
+  extension for [mdbook](https://github.com/rust-lang/mdBook/)'s HTML renderer.
 
 ## Showcases
 
@@ -39,11 +41,17 @@ cargo install mdbook-i18n-helpers
 Please see [USAGE](i18n-helpers/USAGE.md) for how to translate your
 [mdbook](https://github.com/rust-lang/mdBook/) project.
 
-## Changelog
-
 Please see the [i18n-helpers/CHANGELOG](CHANGELOG) for details on the changes in
 each release.
 
+### `mdbook-tera-backend`
+
+Run
+
+```shell
+$ cargo install mdbook-tera-backend
+```
+
 ## Contact
 
 For questions or comments, please contact

mdbook-tera-backend/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "mdbook-tera-backend"
+version = "0.0.1"
+authors = ["Martin Geisler <mgeisler@google.com>", "Alexandre Senges <asenges@google.com>"]
+categories = ["template-engine"]
+edition = "2021"
+keywords = ["mdbook", "tera", "renderer", "template"]
+license = "Apache-2.0"
+repository = "https://github.com/google/mdbook-i18n-helpers"
+description = "Plugin to extend mdbook with Tera templates and custom HTML components."
+
+[dependencies]
+anyhow = "1.0.75"
+mdbook = { version = "0.4.25", default-features = false }
+serde = "1.0"
+serde_json = "1.0.91"
+tera = "1.19.1"
+
+[dev-dependencies]
+tempdir = "0.3.7"

mdbook-tera-backend/README.md

@@ -0,0 +1,80 @@
+# Tera backend extension for `mdbook`
+
+[![Visit crates.io](https://img.shields.io/crates/v/mdbook-i18n-helpers?style=flat-square)](https://crates.io/crates/mdbook-tera-backend)
+[![Build workflow](https://img.shields.io/github/actions/workflow/status/google/mdbook-i18n-helpers/test.yml?style=flat-square)](https://github.com/google/mdbook-i18n-helpers/actions/workflows/test.yml?query=branch%3Amain)
+[![GitHub contributors](https://img.shields.io/github/contributors/google/mdbook-i18n-helpers?style=flat-square)](https://github.com/google/mdbook-i18n-helpers/graphs/contributors)
+[![GitHub stars](https://img.shields.io/github/stars/google/mdbook-i18n-helpers?style=flat-square)](https://github.com/google/mdbook-i18n-helpers/stargazers)
+
+This `mdbook` backend makes it possible to use
+[tera](https://github.com/Keats/tera) templates and expand the capabilities of
+your books. It works on top of the default HTML backend.
+
+## Installation
+
+Run
+
+```shell
+$ cargo install mdbook-tera-backend
+```
+
+## Usage
+
+### Configuring the backend
+
+To enable the backend, simply add `[output.tera-backend]` to your `book.toml`,
+and configure the place where youre templates will live. For instance
+`theme/templates`:
+
+```toml
+[output.html] # You must still enable the html backend.
+[output.tera-backend]
+template_dir = "theme/templates"
+```
+
+### Creating templates
+
+Create your template files in the same directory as your book.
+
+```html
+<!-- ./theme/templates/hello_world.html -->
+<div>
+  Hello world!
+</div>
+```
+
+### Using templates in `index.hbs`
+
+Since the HTML renderer will first render Handlebars templates, we need to tell
+it to ignore Tera templates using `{{{{raw}}}}` blocks:
+
+```html
+{{{{raw}}}}
+{% set current_language = ctx.config.book.language %}
+<p>Current language: {{ current_language }}</p>
+{% include "hello_world.html" %}
+{{{{/raw}}}}
+```
+
+Includes names are based on the file name and not the whole file path.
+
+### Tera documentation
+
+Find out all you can do with Tera templates
+[here](https://keats.github.io/tera/docs/).
+
+## Changelog
+
+Please see [CHANGELOG](../CHANGELOG.md) for details on the changes in each
+release.
+
+## Contact
+
+For questions or comments, please contact
+[Martin Geisler](mailto:mgeisler@google.com) or
+[Alexandre Senges](mailto:asenges@google.come) or start a
+[discussion](https://github.com/google/mdbook-i18n-helpers/discussions). We
+would love to hear from you.
+
+---
+
+This is not an officially supported Google product.

mdbook-tera-backend/src/main.rs

@@ -0,0 +1,35 @@
+mod tera_renderer;
+
+use anyhow::{anyhow, Context};
+use mdbook::renderer::RenderContext;
+use std::io;
+
+use crate::tera_renderer::custom_component::TeraRendererConfig;
+use crate::tera_renderer::renderer::Renderer;
+
+/// Re-renders HTML files outputed by the HTML backend with Tera templates.
+/// Please make sure the HTML backend is enabled.
+fn main() -> anyhow::Result<()> {
+    let mut stdin = io::stdin();
+    let ctx = RenderContext::from_json(&mut stdin).unwrap();
+    if ctx.config.get_renderer("html").is_none() {
+        return Err(anyhow!(
+            "Could not find the HTML backend. Please make sure the HTML backend is enabled."
+        ));
+    }
+    let config: TeraRendererConfig = ctx
+        .config
+        .get_deserialized_opt("output.tera-backend")
+        .context("Failed to get tera-backend config")?
+        .context("No tera-backend config found")?;
+
+    let tera_template = config
+        .create_template(&ctx.root)
+        .context("Failed to create components")?;
+
+    let mut renderer = Renderer::new(ctx, tera_template);
+
+    renderer.render_book().context("Failed to render book")?;
+
+    Ok(())
+}

mdbook-tera-backend/src/tera_renderer.rs

@@ -0,0 +1,2 @@
+pub mod custom_component;
+pub mod renderer;

mdbook-tera-backend/src/tera_renderer/custom_component.rs

@@ -0,0 +1,37 @@
+use anyhow::Result;
+use serde::Deserialize;
+use std::path::{Path, PathBuf};
+use tera::Tera;
+
+/// Configuration in `book.toml` `[output.tera-renderer]`.
+#[derive(Deserialize)]
+pub struct TeraRendererConfig {
+    /// Relative path to the templates directory from the `book.toml` directory.
+    pub template_dir: Option<PathBuf>,
+}
+
+/// Recursively add all templates in the `template_dir` to the `tera_template`.
+fn add_templates_recursively(tera_template: &mut Tera, directory: &Path) -> Result<()> {
+    for entry in std::fs::read_dir(directory)? {
+        let entry = entry?;
+        let path = entry.path();
+        if path.is_dir() {
+            add_templates_recursively(tera_template, &path)?;
+        } else {
+            tera_template.add_template_file(&path, path.file_name().unwrap().to_str())?;
+        }
+    }
+    Ok(())
+}
+
+impl TeraRendererConfig {
+    /// Create the `tera_template` and add all templates in the `template_dir` to it.
+    pub fn create_template(&self, current_dir: &Path) -> Result<Tera> {
+        let mut tera_template = Tera::default();
+        if let Some(template_dir) = &self.template_dir {
+            add_templates_recursively(&mut tera_template, &current_dir.join(template_dir))?;
+        }
+
+        Ok(tera_template)
+    }
+}

mdbook-tera-backend/src/tera_renderer/renderer.rs

@@ -0,0 +1,174 @@
+use anyhow::{anyhow, Result};
+use mdbook::renderer::RenderContext;
+use std::path::Path;
+use tera::Tera;
+
+/// Renderer for the tera backend.
+///
+/// This will read all the files in the `RenderContext` and render them using the `Tera` template.
+/// ```
+pub struct Renderer {
+    ctx: RenderContext,
+    tera_template: Tera,
+}
+
+impl Renderer {
+    /// Create a new `Renderer` from the `RenderContext` and `Tera` template.
+    pub fn new(ctx: RenderContext, tera_template: Tera) -> Self {
+        Renderer { ctx, tera_template }
+    }
+
+    /// Render the book. This goes through the output of the HTML renderer
+    /// by considering all the output HTML files as input to the Tera template.
+    /// It overwrites the preexisting files with their Tera-rendered version.
+    pub fn render_book(&mut self) -> Result<()> {
+        let dest_dir = self.ctx.destination.parent().unwrap().join("html");
+        if !dest_dir.is_dir() {
+            return Err(anyhow!(
+                "{dest_dir:?} is not a directory. Please make sure the HTML renderer is enabled."
+            ));
+        }
+        self.render_book_directory(&dest_dir)
+    }
+
+    /// Render the book directory located at `path` recursively.
+    fn render_book_directory(&mut self, path: &Path) -> Result<()> {
+        for entry in path.read_dir()? {
+            let entry = entry?;
+            let path = entry.path();
+            if path.is_dir() {
+                self.render_book_directory(&path)?;
+            } else {
+                self.process_file(&path)?;
+            }
+        }
+        Ok(())
+    }
+
+    /// Reads the file at `path` and renders it.
+    fn process_file(&mut self, path: &Path) -> Result<()> {
+        if path.extension().unwrap_or_default() != "html" {
+            return Ok(());
+        }
+        let file_content = std::fs::read_to_string(path)?;
+        let output = self.render_file_content(&file_content, path)?;
+        Ok(std::fs::write(path, output)?)
+    }
+
+    /// Creates the rendering context to be passed to the templates.
+    ///
+    /// # Arguments
+    ///
+    /// `path`: The path to the file that will be added as extra context to the renderer.
+    fn create_context(&mut self, path: &Path) -> Result<tera::Context> {
+        let mut context = tera::Context::new();
+        let book_dir = self.ctx.destination.parent().unwrap();
+        let relative_path = path.strip_prefix(book_dir).unwrap();
+        context.insert("path", &relative_path);
+        context.insert("book_dir", &self.ctx.destination.parent().unwrap());
+
+        Ok(context)
+    }
+
+    /// Rendering logic for an individual file.
+    fn render_file_content(&mut self, file_content: &str, path: &Path) -> Result<String> {
+        let tera_context = self.create_context(path)?;
+
+        let rendered_file = self
+            .tera_template
+            .render_str(file_content, &tera_context)
+            .map_err(|e| anyhow!("Error rendering file {path:?}: {e:?}"))?;
+        Ok(rendered_file)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use tempdir::TempDir;
+
+    use super::*;
+    use crate::tera_renderer::custom_component::TeraRendererConfig;
+    use anyhow::Result;
+
+    const RENDER_CONTEXT_STR: &str = r#"
+    {
+        "version":"0.4.32",
+        "root":"",
+        "book":{
+           "sections": [],
+           "__non_exhaustive": null
+        },
+        "destination": "",
+        "config":{
+           "book":{
+              "authors":[
+                 "Martin Geisler"
+              ],
+              "language":"en",
+              "multilingual":false,
+              "src":"src",
+              "title":"Comprehensive Rust 🦀"
+           },
+           "build":{
+              "build-dir":"book",
+              "use-default-preprocessors":true
+           },
+           "output":{
+              "tera-backend": {
+                    "template_dir": "templates"
+              },
+              "renderers":[
+                 "html",
+                 "tera-backend"
+              ]
+           }
+        }
+     }"#;
+
+    const HTML_FILE: &str = r#"
+        <!DOCTYPE html>
+            {% include "test_template.html" %}
+            PATH: {{ path }}
+        </html>
+    "#;
+
+    const TEMPLATE_FILE: &str = "RENDERED";
+
+    const RENDERED_HTML_FILE: &str = r#"
+        <!DOCTYPE html>
+            RENDERED
+            PATH: html/test.html
+        </html>
+    "#;
+
+    #[test]
+    fn test_renderer() -> Result<()> {
+        let mut ctx = RenderContext::from_json(RENDER_CONTEXT_STR.as_bytes()).unwrap();
+
+        let tmp_dir = TempDir::new("output")?;
+        let html_path = tmp_dir.path().join("html");
+        let templates_path = tmp_dir.path().join("templates");
+
+        std::fs::create_dir(&html_path)?;
+        std::fs::create_dir(&templates_path)?;
+
+        let html_file_path = html_path.join("test.html");
+        std::fs::write(&html_file_path, HTML_FILE)?;
+        std::fs::write(templates_path.join("test_template.html"), TEMPLATE_FILE)?;
+
+        ctx.destination = tmp_dir.path().join("tera-renderer");
+        ctx.root = tmp_dir.path().to_owned();
+
+        let config: TeraRendererConfig = ctx
+            .config
+            .get_deserialized_opt("output.tera-backend")?
+            .ok_or_else(|| anyhow!("No tera backend configuration."))?;
+
+        let tera_template = config.create_template(&ctx.root)?;
+        let mut renderer = Renderer::new(ctx, tera_template);
+        renderer.render_book().expect("Failed to render book");
+
+        assert_eq!(std::fs::read_to_string(html_file_path)?, RENDERED_HTML_FILE);
+        Ok(())
+    }
+}