mdbook: add build info, like we do on Pan Docs (#164)

Author: avivace

preproc/src/git.rs

@@ -0,0 +1,70 @@
+/*
+ * This Source Code Form is subject to the
+ * terms of the Mozilla Public License, v.
+ * 2.0. If a copy of the MPL was not
+ * distributed with this file, You can
+ * obtain one at
+ * http://mozilla.org/MPL/2.0/.
+ */
+
+use std::process::{Command, Stdio};
+
+use anyhow::Error;
+
+#[derive(Debug)]
+pub struct Commit {
+    info: String,
+    splits: [usize; 2],
+}
+
+impl Commit {
+    pub fn rev_parse(what: &str) -> Result<Self, Error> {
+        let output = Command::new("git")
+            .args([
+                "--git-dir=.git",
+                "show",
+                "-s",
+                "--format=%H%x00%h%x00%ci",
+                what,
+            ])
+            .stderr(Stdio::inherit())
+            .stdin(Stdio::null())
+            .output()
+            .expect("Failed to get commit info");
+        if !output.status.success() {
+            return Err(Error::msg(format!(
+                "Git exited with status {} while getting commit info",
+                output.status
+            )));
+        }
+        let mut info = String::from_utf8(output.stdout).expect("Commit info is not valid UTF-8??");
+        let trimmed_len = info.trim_end().len();
+        info.truncate(trimmed_len);
+
+        let first_split = info
+            .find('\0')
+            .expect("Failed to split hash and short hash");
+        let second_split = info[first_split + 1..]
+            .find('\0')
+            .expect("Failed to split short hash and timestamp")
+            + first_split
+            + 1;
+
+        Ok(Self {
+            info,
+            splits: [first_split, second_split],
+        })
+    }
+
+    pub fn hash(&self) -> &str {
+        &self.info[..self.splits[0]]
+    }
+
+    pub fn short_hash(&self) -> &str {
+        &self.info[self.splits[0] + 1..self.splits[1]]
+    }
+
+    pub fn timestamp(&self) -> &str {
+        &self.info[self.splits[1] + 1..]
+    }
+}

preproc/src/main.rs

@@ -14,9 +14,10 @@ use std::io;
 use std::process;
 
 mod admonitions;
+mod git;
+mod links;
 mod preproc;
 use preproc::GbAsmTut;
-mod links;
 
 pub fn make_app() -> App<'static, 'static> {
     App::new("pandocs-preproc")

preproc/src/preproc.rs

@@ -7,6 +7,7 @@
  * http://mozilla.org/MPL/2.0/.
  */
 
+use crate::git::Commit;
 use crate::links;
 use anyhow::Result;
 use mdbook::book::{Book, BookItem};
@@ -33,6 +34,12 @@ impl Preprocessor for GbAsmTut {
     fn run(&self, ctx: &PreprocessorContext, mut book: Book) -> Result<Book, Error> {
         let src_dir = ctx.root.join(&ctx.config.book.src);
 
+        let commit = if ctx.root.join(".git").exists() {
+            Some(Commit::rev_parse("HEAD")?)
+        } else {
+            None
+        };
+
         let mut res = Ok(());
         book.for_each_mut(|section: &mut BookItem| {
             if res.is_err() {
@@ -50,6 +57,17 @@ impl Preprocessor for GbAsmTut {
                     if let Err(err) = self.process_admonitions(ch) {
                         res = Err(err);
                     }
+
+                    if ch.name == "Home" {
+                        if let Some(ref commit) = commit {
+                            ch.content.push_str(&format!(
+                                "\n\n\n <small>This document version was produced from git commit [`{}`](https://github.com/gbdev/gb-asm-tutorial/tree/{}) ({}).</small>\n",
+                                commit.short_hash(),
+                                commit.hash(),
+                                commit.timestamp(),
+                            ));
+                        }
+                    }
                 }
             }
         });