book: add snippets processor

Remove the four spaces in snippets when using anchors.

Signed-off-by: Yuki Kishimoto <[email protected]>

book/book.toml

@@ -22,3 +22,6 @@ git-repository-url = "https://github.com/rust-nostr/nostr"
 [preprocessor.admonish]
 command = "mdbook-admonish"
 assets_version = "3.0.2" # do not edit: managed by `mdbook-admonish install`
+
+[preprocessor.snippets]
+after = ["links"]

book/justfile

@@ -3,6 +3,7 @@ init:
 	@mdbook --version || cargo install mdbook --version 0.4.40
 	@mdbook-linkcheck --version || cargo install mdbook-linkcheck --version 0.7.7
 	@mdbook-admonish --version || cargo install mdbook-admonish --version 1.15.0
+	@mdbook-snippets --version || cargo install --path ./snippets-processor
 
 build: init
 	mdbook build

book/snippets-processor/.gitignore

@@ -0,0 +1 @@
+target/

book/snippets-processor/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "mdbook-snippets"
+version = "0.1.0"
+edition = "2021"
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[dependencies]
+clap = "4.5"
+mdbook = "=0.4.40"
+serde_json = "1.0"

book/snippets-processor/src/main.rs

@@ -0,0 +1,127 @@
+// Copied from https://github.com/breez/breez-sdk-docs/tree/74f018a647820ce515a564083b9986157ee7f894/snippets-processor
+
+use std::io;
+
+use clap::{crate_version, Arg, ArgMatches, Command};
+use mdbook::book::Book;
+use mdbook::errors::{Error, Result};
+use mdbook::preprocess::{CmdPreprocessor, Preprocessor, PreprocessorContext};
+use mdbook::BookItem;
+
+fn main() -> Result<()> {
+    // set up app
+    let matches = make_app().get_matches();
+    let pre = SnippetsProcessor;
+
+    // determine what behaviour has been requested
+    if let Some(sub_args) = matches.subcommand_matches("supports") {
+        // handle cmdline supports
+        handle_supports(&pre, sub_args)
+    } else {
+        // handle preprocessing
+        handle_preprocessing(&pre)
+    }
+}
+
+/// Parse CLI options.
+pub fn make_app() -> Command {
+    Command::new("mdbook-snippets")
+        .version(crate_version!())
+        .about("A preprocessor that removes leading whitespace from code snippets.")
+        .subcommand(
+            Command::new("supports")
+                .arg(Arg::new("renderer").required(true))
+                .about("Check whether a renderer is supported by this preprocessor"),
+        )
+}
+
+/// Tell mdBook if we support what it asks for.
+fn handle_supports(pre: &dyn Preprocessor, sub_args: &ArgMatches) -> Result<()> {
+    let renderer = sub_args
+        .get_one::<String>("renderer")
+        .expect("Required argument");
+    let supported = pre.supports_renderer(renderer);
+    if supported {
+        Ok(())
+    } else {
+        Err(Error::msg(format!(
+            "The snippets preprocessor does not support the '{renderer}' renderer",
+        )))
+    }
+}
+
+/// Preprocess `book` using `pre` and print it out.
+fn handle_preprocessing(pre: &dyn Preprocessor) -> Result<()> {
+    let (ctx, book) = CmdPreprocessor::parse_input(io::stdin())?;
+    check_mdbook_version(&ctx.mdbook_version);
+
+    let processed_book = pre.run(&ctx, book)?;
+    serde_json::to_writer(io::stdout(), &processed_book)?;
+    Ok(())
+}
+
+/// Produce a warning on mdBook version mismatch.
+fn check_mdbook_version(version: &str) {
+    if version != mdbook::MDBOOK_VERSION {
+        eprintln!(
+            "This mdbook-snippets was built against mdbook v{}, \
+            but we are being called from mdbook v{version}. \
+            If you have any issue, this might be a reason.",
+            mdbook::MDBOOK_VERSION,
+        )
+    }
+}
+
+struct SnippetsProcessor;
+impl Preprocessor for SnippetsProcessor {
+    fn name(&self) -> &str {
+        "snippets"
+    }
+
+    fn run(&self, _ctx: &PreprocessorContext, mut book: Book) -> Result<Book> {
+        book.for_each_mut(|item| {
+            if let BookItem::Chapter(chapter) = item {
+                let mut resulting_lines: Vec<String> = vec![];
+                let mut in_block = false;
+                let mut block_lines: Vec<String> = vec![];
+                let mut min_indentation: usize = 0;
+                for line in chapter.content.lines() {
+                    if line.starts_with("```") {
+                        if in_block {
+                            // This is end of block
+                            // Replace previous lines
+                            for block_line in block_lines.iter().cloned() {
+                                let indent = std::cmp::min(min_indentation, block_line.len());
+                                resulting_lines.push(block_line[indent..].to_string())
+                            }
+                            in_block = false;
+                        } else {
+                            // Start of block
+                            in_block = true;
+                            block_lines = vec![];
+                            min_indentation = usize::MAX;
+                        }
+
+                        resulting_lines.push(line.to_string());
+                        continue;
+                    }
+
+                    if in_block {
+                        let line = line.replace('\t', "    ");
+                        block_lines.push(line.clone());
+                        let trimmed = line.trim_start_matches(' ');
+                        if !trimmed.is_empty() {
+                            min_indentation =
+                                std::cmp::min(min_indentation, line.len() - trimmed.len())
+                        }
+                    } else {
+                        resulting_lines.push(line.to_string());
+                    }
+                }
+
+                chapter.content = resulting_lines.join("\n");
+            }
+        });
+        Ok(book)
+    }
+}