Rename directory to match crate name.

mdbook-exerciser/Cargo.toml

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+[package]
+name = "mdbook-exerciser"
+version = "0.1.0"
+edition = "2021"
+license = "Apache-2.0"
+authors = ["Andrew Walbran <qwandor@google.com>"]
+description = "A tool for extracting starter code for exercises from Markdown files."
+repository = "https://github.com/google/comprehensive-rust"
+
+[dependencies]
+anyhow = "1.0.68"
+log = "0.4.17"
+mdbook = "0.4.25"
+pretty_env_logger = "0.4.0"
+pulldown-cmark = { version = "0.9.2", default-features = false }

mdbook-exerciser/README.md

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+# exerciser
+
+This is an mdBook renderer to generate templates for exercises from the Markdown source. Given a
+Markdown file `example.md` with one or more sections like:
+
+````markdown
+<!-- File src/main.rs -->
+
+```rust,compile_fail
+{{#include example/src/main.rs:main}}
+
+fn some_more_code() {
+    // TODO: Write some Rust code here.
+}
+```
+````
+
+It will create a file `book/exerciser/exercise-templates/example/src/main.rs` with the appropriate
+contents.

mdbook-exerciser/src/lib.rs

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+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use log::{info, trace};
+use pulldown_cmark::{Event, Parser, Tag};
+use std::{
+    fs::{create_dir_all, File},
+    io::Write,
+    path::Path,
+};
+
+const FILENAME_START: &str = "<!-- File ";
+const FILENAME_END: &str = " -->";
+
+pub fn process(output_directory: &Path, input_contents: &str) -> anyhow::Result<()> {
+    let parser = Parser::new(input_contents);
+
+    // Find a specially-formatted comment followed by a code block, and then call `write_output`
+    // with the contents of the code block, to write to a file named by the comment. Code blocks
+    // without matching comments will be ignored, as will comments which are not followed by a code
+    // block.
+    let mut next_filename: Option<String> = None;
+    let mut current_file: Option<File> = None;
+    for event in parser {
+        trace!("{:?}", event);
+        match event {
+            Event::Html(html) => {
+                let html = html.trim();
+                if html.starts_with(FILENAME_START) && html.ends_with(FILENAME_END) {
+                    next_filename = Some(
+                        html[FILENAME_START.len()..html.len() - FILENAME_END.len()]
+                            .to_string(),
+                    );
+                    info!("Next file: {:?}:", next_filename);
+                }
+            }
+            Event::Start(Tag::CodeBlock(x)) => {
+                info!("Start {:?}", x);
+                if let Some(filename) = &next_filename {
+                    let full_filename = output_directory.join(filename);
+                    info!("Opening {:?}", full_filename);
+                    if let Some(directory) = full_filename.parent() {
+                        create_dir_all(directory)?;
+                    }
+                    current_file = Some(File::create(full_filename)?);
+                    next_filename = None;
+                }
+            }
+            Event::Text(text) => {
+                info!("Text: {:?}", text);
+                if let Some(output_file) = &mut current_file {
+                    output_file.write(text.as_bytes())?;
+                }
+            }
+            Event::End(Tag::CodeBlock(x)) => {
+                info!("End   {:?}", x);
+                current_file = None;
+            }
+            _ => {}
+        }
+    }
+
+    Ok(())
+}

mdbook-exerciser/src/main.rs

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+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use anyhow::Context;
+use log::trace;
+use mdbook::{book::Book, renderer::RenderContext, BookItem};
+use mdbook_exerciser::process;
+use std::{
+    fs::{create_dir, remove_dir_all},
+    io::stdin,
+    path::Path,
+};
+
+fn main() -> anyhow::Result<()> {
+    pretty_env_logger::init();
+
+    let context = RenderContext::from_json(&mut stdin()).context("Parsing stdin")?;
+
+    let config = context
+        .config
+        .get_renderer("exerciser")
+        .context("Missing output.exerciser configuration")?;
+
+    let output_directory = Path::new(
+        config
+            .get("output-directory")
+            .context("Missing output.exerciser.output-directory configuration value")?
+            .as_str()
+            .context("Expected a string for output.exerciser.output-directory")?,
+    );
+
+    let _ = remove_dir_all(output_directory);
+    create_dir(output_directory).with_context(|| {
+        format!("Failed to create output directory {:?}", output_directory)
+    })?;
+
+    process_all(&context.book, output_directory)?;
+
+    Ok(())
+}
+
+fn process_all(book: &Book, output_directory: &Path) -> anyhow::Result<()> {
+    for item in book.iter() {
+        if let BookItem::Chapter(chapter) = item {
+            trace!("Chapter {:?} / {:?}", chapter.path, chapter.source_path);
+            if let Some(chapter_path) = &chapter.path {
+                // Put the exercises in a subdirectory named after the chapter file, without its
+                // parent directories.
+                let chapter_output_directory =
+                    output_directory.join(chapter_path.file_stem().with_context(
+                        || format!("Chapter {:?} has no file stem", chapter_path),
+                    )?);
+                process(&chapter_output_directory, &chapter.content)?;
+            }
+        }
+    }
+
+    Ok(())
+}