write_since(): Output file paths relative to the current directory

Previously, the file paths of TODO lines in the output were relative to
the repository root. When you're in a subdirectory, though, this makes
them harder to work with, as they're relative paths, but aren't relative
to the current working directory.

Change the file path output so that paths are relative to the current
directory instead of the repo root.

2 files changed, 109 insertions, 1 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 910b488..7adfb2f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -17,6 +17,7 @@
 #![warn(rust_2018_idioms)]
 
 use std::io::Write;
+use std::path::{Path, PathBuf};
 
 use git2::{DiffOptions, Repository, Tree};
 use thiserror::Error;
@@ -71,7 +72,7 @@ impl Todos<'_> {
                                     write!(
                                         write_to,
                                         "{}:{}:{}",
-                                        path.display(),
+                                        relative_path(self.repo, path).display(),
                                         line_number,
                                         l,
                                     ).expect("write error");
@@ -95,3 +96,29 @@ impl Todos<'_> {
         Ok(master.get().peel_to_tree()?)
     }
 }
+
+/// Get `path` relative to the current directory.
+///
+/// Attempt to remove the current directory prefix from `path` to turn it into a
+/// relative path from the current directory.
+fn relative_path(repo: &Repository, path: &Path) -> PathBuf {
+    let workdir = match repo.workdir() {
+        Some(d) => d,
+        None => return path.to_path_buf(),
+    };
+
+    let current_dir = match std::env::current_dir() {
+        Ok(d) => d,
+        Err(_) => return path.to_path_buf(),
+    };
+
+    let current_dir_relative = match current_dir.strip_prefix(workdir) {
+        Ok(d) => d,
+        Err(_) => return path.to_path_buf(),
+    };
+
+    match path.strip_prefix(current_dir_relative) {
+        Ok(d) => d.to_path_buf(),
+        Err(_) => path.to_path_buf(),
+    }
+}
diff --git a/t/108-file-path-is-relative.t b/t/108-file-path-is-relative.t
new file mode 100644
index 0000000..44a489f
--- /dev/null
+++ b/t/108-file-path-is-relative.t
@@ -0,0 +1,81 @@
+#!/usr/bin/env perl -w
+
+# Copyright (c) 2020  Teddy Wing
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+
+use strict;
+
+use File::Copy;
+use File::Path qw(remove_tree);
+use Test::More;
+
+use Bin qw($BIN);
+
+my $file = 'git-sugdiff.rs';
+
+mkdir 't-git-repo/subdir' or die $!;
+chdir 't-git-repo/subdir' or die $!;
+
+move("../$file", $file);
+
+system('git add git-sugdiff.rs');
+ok !$?;
+
+system('git commit -m "Move git-sugdiff.rs"');
+ok !$?;
+
+system('git checkout -b fork-point');
+ok !$?;
+
+open(my $input, '<', $file) or die $!;
+open(my $output, '>', "$file.out") or die $!;
+
+while (<$input>) {
+	if ($. == 34) {
+		print $output "    // TODO: 100-shows-todo-comments-since-fork-point\n";
+	}
+
+	print $output $_;
+}
+
+close $input;
+close $output;
+
+move("$file.out", $file) or die $!;
+
+system('git add git-sugdiff.rs');
+ok !$?;
+
+system('git commit -m "New TODO"');
+ok !$?;
+
+my $todos = qx($BIN);
+is $todos, 'git-sugdiff.rs:34:    // TODO: 100-shows-todo-comments-since-fork-point
+';
+
+
+# Teardown
+system('git checkout master');
+system('git branch -D fork-point');
+
+system('git reset --hard HEAD~1');
+ok !$?;
+
+chdir '..' or die $!;
+remove_tree('subdir');
+
+
+done_testing;