feat: Adds Git State module for showing "REBASING 2/3", etc. (#276)

- Adds the git_state module.
- Adds git_state to the default prompt order
- Updates the documentation to describe the git_state module

src/modules/git_state.rs

@@ -0,0 +1,166 @@
+use ansi_term::Color;
+use git2::{Repository, RepositoryState};
+use std::path::Path;
+
+use super::{Context, Module};
+
+/// Creates a module with the state of the git repository at the current directory
+///
+/// During a git operation it will show: REBASING, BISECTING, MERGING, etc.
+/// If the progress information is available (e.g. rebasing 3/10), it will show that too.
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("git_state")?;
+
+    let repo_root = context.repo_root.as_ref()?;
+    let mut repository = Repository::open(repo_root).ok()?;
+    let state_description = get_state_description(&mut repository);
+
+    if let StateDescription::Clean = state_description {
+        return None;
+    }
+
+    module.get_prefix().set_value("(");
+    module.get_suffix().set_value(") ");
+    module.set_style(Color::Yellow.bold());
+
+    let label = match state_description {
+        StateDescription::Label(label) => label,
+        StateDescription::LabelAndProgress(label, _) => label,
+        // Should only be possible if you've added a new variant to StateDescription
+        _ => panic!("Expected to have a label at this point in the control flow."),
+    };
+
+    module.new_segment(label.segment_name, label.message_default);
+
+    if let StateDescription::LabelAndProgress(_, progress) = state_description {
+        module.new_segment("progress_current", &format!(" {}", progress.current));
+        module.new_segment("progress_divider", "/");
+        module.new_segment("progress_total", &format!("{}", progress.total));
+    }
+
+    Some(module)
+}
+
+static MERGE_LABEL: StateLabel = StateLabel {
+    segment_name: "merge",
+    message_default: "MERGING",
+};
+
+static REVERT_LABEL: StateLabel = StateLabel {
+    segment_name: "revert",
+    message_default: "REVERTING",
+};
+
+static CHERRY_LABEL: StateLabel = StateLabel {
+    segment_name: "cherry_pick",
+    message_default: "CHERRY-PICKING",
+};
+
+static BISECT_LABEL: StateLabel = StateLabel {
+    segment_name: "bisect",
+    message_default: "BISECTING",
+};
+
+static AM_LABEL: StateLabel = StateLabel {
+    segment_name: "am",
+    message_default: "AM",
+};
+
+static REBASE_LABEL: StateLabel = StateLabel {
+    segment_name: "rebase",
+    message_default: "REBASING",
+};
+
+static AM_OR_REBASE_LABEL: StateLabel = StateLabel {
+    segment_name: "am_or_rebase",
+    message_default: "AM/REBASE",
+};
+
+fn get_state_description(repository: &mut Repository) -> StateDescription {
+    match repository.state() {
+        RepositoryState::Clean => StateDescription::Clean,
+        RepositoryState::Merge => StateDescription::Label(&MERGE_LABEL),
+        RepositoryState::Revert => StateDescription::Label(&REVERT_LABEL),
+        RepositoryState::RevertSequence => StateDescription::Label(&REVERT_LABEL),
+        RepositoryState::CherryPick => StateDescription::Label(&CHERRY_LABEL),
+        RepositoryState::CherryPickSequence => StateDescription::Label(&CHERRY_LABEL),
+        RepositoryState::Bisect => StateDescription::Label(&BISECT_LABEL),
+        RepositoryState::ApplyMailbox => StateDescription::Label(&AM_LABEL),
+        RepositoryState::ApplyMailboxOrRebase => StateDescription::Label(&AM_OR_REBASE_LABEL),
+        RepositoryState::Rebase => describe_rebase(repository),
+        RepositoryState::RebaseInteractive => describe_rebase(repository),
+        RepositoryState::RebaseMerge => describe_rebase(repository),
+    }
+}
+
+fn describe_rebase(repository: &mut Repository) -> StateDescription {
+    /*
+     *  Sadly, libgit2 seems to have some issues with reading the state of
+     *  interactive rebases. So, instead, we'll poke a few of the .git files
+     *  ourselves. This might be worth re-visiting this in the future...
+     *
+     *  The following is based heavily on: https://github.com/magicmonty/bash-git-prompt
+     */
+
+    let just_label = StateDescription::Label(&REBASE_LABEL);
+
+    let dot_git = repository
+        .workdir()
+        .and_then(|d| Some(d.join(Path::new(".git"))));
+
+    let dot_git = match dot_git {
+        None => {
+            // We didn't find the .git directory.
+            // Something very odd is going on. We'll just back away slowly.
+            return just_label;
+        }
+        Some(path) => path,
+    };
+
+    let has_path = |relative_path: &str| {
+        let path = dot_git.join(Path::new(relative_path));
+        path.exists()
+    };
+
+    let file_to_usize = |relative_path: &str| {
+        let path = dot_git.join(Path::new(relative_path));
+        let contents = crate::utils::read_file(path).ok()?;
+        let quantity = contents.trim().parse::<usize>().ok()?;
+        Some(quantity)
+    };
+
+    let paths_to_progress = |current_path: &str, total_path: &str| {
+        let current = file_to_usize(current_path)?;
+        let total = file_to_usize(total_path)?;
+        Some(StateProgress { current, total })
+    };
+
+    let progress = if has_path("rebase-merge") {
+        paths_to_progress("rebase-merge/msgnum", "rebase-merge/end")
+    } else if has_path("rebase-apply") {
+        paths_to_progress("rebase-apply/next", "rebase-apply/last")
+    } else {
+        None
+    };
+
+    match progress {
+        None => just_label,
+        Some(progress) => StateDescription::LabelAndProgress(&REBASE_LABEL, progress),
+    }
+}
+
+enum StateDescription {
+    Clean,
+    Label(&'static StateLabel),
+    LabelAndProgress(&'static StateLabel, StateProgress),
+}
+
+struct StateLabel {
+    segment_name: &'static str,
+    message_default: &'static str,
+}
+
+struct StateProgress {
+    current: usize,
+    total: usize,
+}

src/modules/mod.rs

@@ -3,6 +3,7 @@ mod character;
 mod cmd_duration;
 mod directory;
 mod git_branch;
+mod git_state;
 mod git_status;
 mod golang;
 mod hostname;
@@ -34,6 +35,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
         "line_break" => line_break::module(context),
         "package" => package::module(context),
         "git_branch" => git_branch::module(context),
+        "git_state" => git_state::module(context),
         "git_status" => git_status::module(context),
         "username" => username::module(context),
         #[cfg(feature = "battery")]