Provide porcelain output for scripts.

Cargo.toml

@@ -40,6 +40,8 @@ textwrap = { version = "0.12.1", features = ["terminal_size"] }
 man = { version = "0.3.0", optional = true }
 rson_rs = { version = "0.2.1", optional = true }
 regex = { version = "1.4.2", optional = true }
+serde =  { version = "1.0.117", features = ["derive"] }
+serde_json = "1.0.59"
 
 [dev-dependencies]
 tempfile = "3.1.0"

src/args.rs

@@ -40,6 +40,10 @@ pub struct Args {
     #[clap(long, hidden(true))]
     pub update: bool,
 
+    /// Output for scripting. Options are "json" for full structured output or "local" or "remote" for a list of branches to be deleted.
+    #[clap(long)]
+    pub porcelain: Option<PorcelainFormat>,
+
     /// Prevents too frequent updates. Seconds between updates in seconds. 0 to disable.
     /// [default: 5] [config: trim.updateInterval]
     #[clap(long)]
@@ -127,6 +131,41 @@ fn exclusive_bool(
     }
 }
 
+/// Configuration of --porcelain format.
+#[derive(Debug)]
+pub enum PorcelainFormat {
+    /// List of to-be-deleted local branches
+    LocalBranches,
+    /// List of remote branches to be deleted.
+    RemoteBranches,
+    /// Full structured JSON output
+    JSON,
+}
+
+impl FromStr for PorcelainFormat {
+    type Err = PorcelainFormatParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.trim() {
+            "" => Err(PorcelainFormatParseError {
+                message: "Porcelain format is empty".to_owned(),
+            }),
+            "json" => Ok(PorcelainFormat::JSON),
+            "local" | "l" => Ok(PorcelainFormat::LocalBranches),
+            "remote" | "r" => Ok(PorcelainFormat::RemoteBranches),
+            unknown => Err(PorcelainFormatParseError {
+                message: format!("Unknown porcelain format: {}", unknown),
+            }),
+        }
+    }
+}
+
+#[derive(Error, Debug)]
+#[error("{message}")]
+pub struct PorcelainFormatParseError {
+    message: String,
+}
+
 #[derive(Hash, Eq, PartialEq, Clone, Debug)]
 pub enum Scope {
     All,

src/branch.rs

@@ -3,6 +3,7 @@ use std::convert::TryFrom;
 use anyhow::{Context, Result};
 use git2::{Branch, Config, Direction, Reference, Repository};
 use log::*;
+use serde::Serialize;
 use thiserror::Error;
 
 use crate::config;
@@ -12,7 +13,7 @@ pub trait Refname {
     fn refname(&self) -> &str;
 }
 
-#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Hash, Clone)]
+#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Hash, Clone, Serialize)]
 pub struct LocalBranch {
     pub refname: String,
 }
@@ -83,7 +84,7 @@ impl<'repo> TryFrom<&git2::Reference<'repo>> for LocalBranch {
     }
 }
 
-#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Hash, Clone)]
+#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Hash, Clone, Serialize)]
 pub struct RemoteTrackingBranch {
     pub refname: String,
 }
@@ -181,7 +182,7 @@ pub enum RemoteTrackingBranchStatus {
     None,
 }
 
-#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Hash, Debug)]
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Hash, Debug, Serialize)]
 pub struct RemoteBranch {
     pub remote: String,
     pub refname: String,

src/core.rs

@@ -7,6 +7,7 @@ use crossbeam_channel::unbounded;
 use git2::{BranchType, Config, Repository};
 use log::*;
 use rayon::prelude::*;
+use serde::Serialize;
 
 use crate::args::DeleteFilter;
 use crate::branch::{
@@ -17,12 +18,14 @@ use crate::subprocess::{self, get_worktrees, RemoteHead};
 use crate::util::ForceSendSync;
 use crate::{config, BaseSpec, Git};
 
+#[derive(Serialize)]
 pub struct TrimPlan {
     pub skipped: HashMap<String, SkipSuggestion>,
     pub to_delete: HashSet<ClassifiedBranch>,
     pub preserved: Vec<Preserved>,
 }
 
+#[derive(Serialize)]
 pub struct Preserved {
     pub branch: ClassifiedBranch,
     pub reason: String,
@@ -390,7 +393,7 @@ impl TrimPlan {
     }
 }
 
-#[derive(Clone, Eq, PartialEq)]
+#[derive(Clone, Eq, PartialEq, Serialize)]
 pub enum SkipSuggestion {
     Tracking,
     TrackingRemote(String),
@@ -434,7 +437,7 @@ fn get_protect_pattern<'a, B: Refname>(
     Ok(None)
 }
 
-#[derive(Hash, Eq, PartialEq, Debug, Clone)]
+#[derive(Hash, Eq, PartialEq, Debug, Clone, Serialize)]
 pub enum ClassifiedBranch {
     MergedLocal(LocalBranch),
     Stray(LocalBranch),

src/lib.rs

@@ -3,6 +3,7 @@ mod branch;
 pub mod config;
 mod core;
 mod merge_tracker;
+pub mod porcelain_outputs;
 mod simple_glob;
 mod subprocess;
 mod util;

src/main.rs

@@ -9,8 +9,9 @@ use dialoguer::Confirm;
 use git2::{BranchType, Repository};
 use log::*;
 
-use git_trim::args::Args;
+use git_trim::args::{Args, PorcelainFormat};
 use git_trim::config::{self, get, Config, ConfigValue};
+use git_trim::porcelain_outputs::{print_json, print_local, print_remote};
 use git_trim::{
     delete_local_branches, delete_remote_branches, get_trim_plan, ls_remote_head, remote_update,
     ClassifiedBranch, ForceSendSync, Git, LocalBranch, PlanParam, RemoteHead, RemoteTrackingBranch,
@@ -58,7 +59,23 @@ fn main(args: Args) -> Result<()> {
         },
     )?;
 
-    print_summary(&plan, &git.repo)?;
+    match args.porcelain {
+        None => {
+            print_summary(&plan, &git.repo)?;
+        }
+        Some(PorcelainFormat::LocalBranches) => {
+            print_local(&plan, &git.repo, &mut std::io::stdout())?;
+            return Ok(());
+        }
+        Some(PorcelainFormat::RemoteBranches) => {
+            print_remote(&plan, &git.repo, &mut std::io::stdout())?;
+            return Ok(());
+        }
+        Some(PorcelainFormat::JSON) => {
+            print_json(&plan, &git.repo, &mut std::io::stdout())?;
+            return Ok(());
+        }
+    }
 
     let locals = plan.locals_to_delete();
     let remotes = plan.remotes_to_delete(&git.repo)?;

src/porcelain_outputs.rs

@@ -0,0 +1,53 @@
+use anyhow::Result;
+use git2::Repository;
+
+use crate::TrimPlan;
+
+/// Prints all locally to-be-deleted branches.
+pub fn print_local(
+    plan: &TrimPlan,
+    _repo: &Repository,
+    mut writer: impl std::io::Write,
+) -> Result<()> {
+    let mut merged_locals = Vec::new();
+    for branch in &plan.to_delete {
+        if let Some(local) = branch.local() {
+            merged_locals.push(local.short_name().to_owned());
+        }
+    }
+
+    merged_locals.sort();
+    for branch in merged_locals {
+        writeln!(writer, "{}", branch)?;
+    }
+
+    Ok(())
+}
+
+/// Print all remotely to-be-deleted branches in the form "<remote>/<branch_name>"
+pub fn print_remote(
+    plan: &TrimPlan,
+    repo: &Repository,
+    mut writer: impl std::io::Write,
+) -> Result<()> {
+    let mut merged_remotes = Vec::new();
+    for branch in &plan.to_delete {
+        if let Some(remote) = branch.remote(repo)? {
+            merged_remotes.push(remote);
+        }
+    }
+
+    merged_remotes.sort();
+    for branch in merged_remotes {
+        let branch_name = &branch.refname["/refs/heads".len()..];
+        writeln!(writer, "{}/{}", branch.remote, branch_name)?;
+    }
+
+    Ok(())
+}
+
+pub fn print_json(plan: &TrimPlan, _repo: &Repository, writer: impl std::io::Write) -> Result<()> {
+    serde_json::to_writer(writer, &plan)?;
+
+    Ok(())
+}