Make Unbricked into a submodule

Pulling specific versions of its files via `git2`

Fixes #110 (by keeping the variable even after outliving its usefulness)

Author: ISSOtm

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "unbricked"]
+	path = unbricked
+	url = https://github.com/ISSOtm/unbricked

Cargo.lock

@@ -17,3 +17,4 @@ pulldown-cmark-to-cmark = "6.0.0"
 regex = "1.5.4"
 termcolor = "1.1.2"
 serde_json = "1.0.59"
+git2 = "0.20.2"

preproc/Cargo.toml

@@ -0,0 +1,61 @@
+use std::{
+    collections::{hash_map::Entry, HashMap},
+    path::{Path, PathBuf},
+};
+
+use anyhow::{anyhow, Context};
+use git2::{Blob, Oid, Repository};
+
+#[derive(Default)]
+pub struct Repos(HashMap<PathBuf, Repository>);
+
+impl Repos {
+    pub fn open(&mut self, path: PathBuf) -> mdbook::errors::Result<&Repository> {
+        match self.0.entry(path) {
+            Entry::Occupied(occupied_entry) => Ok(occupied_entry.into_mut()),
+            Entry::Vacant(vacant_entry) => {
+                let repo = Repository::open(vacant_entry.key())?;
+                Ok(vacant_entry.insert(repo))
+            }
+        }
+    }
+}
+
+pub fn find_commit_by_msg(repo: &Repository, msg: &str) -> mdbook::errors::Result<Oid> {
+    let head = repo.head().context("Failed to look up repo HEAD")?;
+    let mut commit = head
+        .peel_to_commit()
+        .context("Failed to get the commit pointed to by HEAD")?;
+    while !commit
+        .message()
+        .ok_or(anyhow!("Non-UTF-8 commit message!?"))?
+        .strip_prefix(msg)
+        .is_some_and(|rest| rest.is_empty() || rest.starts_with('\n'))
+    {
+        commit = commit
+            .parent(0)
+            .context("Failed to find a commit with specified message")?;
+    }
+    Ok(commit.id())
+}
+
+pub fn get_file<'repos>(
+    repos: &'repos Repos,
+    (repo_path, commit_id): &(PathBuf, Oid),
+    path: &Path,
+) -> mdbook::errors::Result<Blob<'repos>> {
+    let repo = &repos.0[repo_path];
+    let commit = repo.find_commit(*commit_id).unwrap();
+    let tree = commit
+        .tree()
+        .context("Unable to obtain the commit's tree")?;
+    let entry = tree
+        .get_path(path)
+        .context("Unable to find the specified file")?;
+    let object = entry
+        .to_object(repo)
+        .context("Unable to obtain the file's object in the repo")?;
+    object
+        .peel_to_blob()
+        .context("The specified path is not a file")
+}