feat: display commit info in --version (#558)

This improves --version output for #554.

build.rs

@@ -7,7 +7,7 @@
 #![allow(clippy::if_same_then_else)]
 
 use rayon::prelude::*;
-use std::path::PathBuf;
+use std::{path::PathBuf, process::Command};
 use version_check as rustc;
 
 struct TreeSitterParser {
@@ -363,4 +363,28 @@ fn main() {
     }
 
     parsers.par_iter().for_each(|p| p.build());
+    commit_info();
+}
+
+fn commit_info() {
+    if !PathBuf::from(".git").exists() {
+        return;
+    }
+
+    let output = match Command::new("git")
+        .arg("log")
+        .arg("-1")
+        .arg("--date=short")
+        .arg("--format=%H %h %cd")
+        .output()
+    {
+        Ok(output) if output.status.success() => output,
+        _ => return,
+    };
+    let stdout = String::from_utf8(output.stdout).unwrap();
+    let mut parts = stdout.split_whitespace();
+    let mut next = || parts.next().unwrap();
+    println!("cargo:rustc-env=DFT_COMMIT_HASH={}", next());
+    println!("cargo:rustc-env=DFT_COMMIT_SHORT_HASH={}", next());
+    println!("cargo:rustc-env=DFT_COMMIT_DATE={}", next())
 }

src/main.rs

@@ -36,6 +36,7 @@ mod options;
 mod parse;
 mod positions;
 mod summary;
+mod version;
 
 #[macro_use]
 extern crate log;

src/options.rs

@@ -2,7 +2,7 @@
 
 use std::{env, ffi::OsStr, path::Path, path::PathBuf};
 
-use clap::{crate_authors, crate_description, crate_version, Arg, Command};
+use clap::{crate_authors, crate_description, Arg, Command};
 use const_format::formatcp;
 use crossterm::tty::IsTty;
 
@@ -10,6 +10,7 @@ use crate::{
     display::style::BackgroundColor,
     exit_codes::EXIT_BAD_ARGUMENTS,
     parse::guess_language::{language_override_from_name, LanguageOverride},
+    version::VERSION,
 };
 
 pub const DEFAULT_BYTE_LIMIT: usize = 1_000_000;
@@ -83,7 +84,7 @@ impl Default for DiffOptions {
 fn app() -> clap::Command<'static> {
     Command::new("Difftastic")
         .override_usage(USAGE)
-        .version(crate_version!())
+        .version(VERSION.as_str())
         .about(crate_description!())
         .author(crate_authors!())
         .after_long_help(concat!(

src/version.rs

@@ -0,0 +1,50 @@
+use std::fmt;
+
+use lazy_static::lazy_static;
+
+pub struct CommitInfo {
+    pub short_commit_hash: &'static str,
+    pub commit_hash: &'static str,
+    pub commit_date: &'static str,
+}
+
+pub struct VersionInfo {
+    pub version: &'static str,
+    pub commit_info: Option<CommitInfo>,
+}
+
+impl fmt::Display for VersionInfo {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.version)?;
+
+        if let Some(ref ci) = &self.commit_info {
+            write!(f, " ({} {})", ci.short_commit_hash, ci.commit_date)?;
+        }
+        Ok(())
+    }
+}
+
+lazy_static! {
+    pub static ref VERSION: String = version().to_string();
+}
+
+pub const fn version() -> VersionInfo {
+    let version = env!("CARGO_PKG_VERSION");
+    let commit_info = match (
+        option_env!("DFT_COMMIT_SHORT_HASH"),
+        option_env!("DFT_COMMIT_HASH"),
+        option_env!("DFT_COMMIT_DATE"),
+    ) {
+        (Some(short_commit_hash), Some(commit_hash), Some(commit_date)) => Some(CommitInfo {
+            short_commit_hash,
+            commit_hash,
+            commit_date,
+        }),
+        _ => None,
+    };
+
+    VersionInfo {
+        version,
+        commit_info,
+    }
+}