feat: support --author flag for git-shortlog

This patch adds support for `--author`, which passes the values straight
to `git-shortlog` [[1]].

Sometimes, it is useful to filter the shortlog by authors. In the past,
people might do this by piping the output of `git-stats` to `grep` or
similar. However, with the introduction of the Totals line, that line
becomes inaccurate.

This way, they can still get an accurate Total by filtering with `git`
directly. This can be useful, for example, for filtering out automated
commits (e.g., dependabot) or non-company contributors.

[1]: https://git-scm.com/docs/git-shortlog

README.md

@@ -53,10 +53,11 @@ Arguments:
   [revision-range]  Show only commits in the specified revision range [default: HEAD]
 
 Options:
-  -e, --email        Show the email address of each author
-  -r, --reviews      Show who reviewed/tested commits based on `Acked-by`, `Tested-by`, and `Reviewed-by` git trailers
-  -s, --sort <SORT>  What column to sort by [default: commits] [possible values: author, commits, files, insertions, deletions, net]
-      --reverse      Whether to reverse the sorting from descending to ascending
-  -h, --help         Print help (see more with '--help')
-  -V, --version      Print version
-  ```
+  -e, --email            Show the email address of each author
+  -r, --reviews          Show who reviewed/tested commits based on `Acked-by`, `Tested-by`, and `Reviewed-by` git trailers
+  -s, --sort <SORT>      What column to sort by [default: commits] [possible values: author, commits, files, insertions, deletions, net]
+      --reverse          Whether to reverse the sorting from descending to ascending
+  -a, --author <AUTHOR>  Limit the commits output to ones with author header lines that match the specified pattern (regular expression)
+  -h, --help             Print help (see more with '--help')
+  -V, --version          Print version
+```

src/main.rs

@@ -39,6 +39,12 @@ struct Cli {
     /// Whether to reverse the sorting from descending to ascending
     #[arg(long)]
     reverse: bool,
+    /// Limit the commits output to ones with author header lines that match the specified pattern (regular expression).
+    ///
+    /// With more than one --author=<pattern>, commits whose author matches any of the given patterns are chosen.
+    /// This is pased through as `--author` to `git shortlog`.
+    #[arg(short, long)]
+    author: Option<Vec<String>>,
 }
 
 #[derive(Clone, ValueEnum)]
@@ -113,12 +119,24 @@ fn main() -> Result<()> {
     });
     yansi::whenever(Condition::cached((HAVE_COLOR)()));
 
+    // Build up the command based on flags
     let rev_range = cli.rev_range;
-    let raw_shortlog = if cli.email {
-        cmd!(sh, "git shortlog -sen {rev_range}").read()?
-    } else {
-        cmd!(sh, "git shortlog -sn {rev_range}").read()?
-    };
+    let author = cli.author.map(|authors| {
+        authors
+            .iter()
+            .map(|a| format!("--author={}", a))
+            .collect::<Vec<String>>()
+    });
+    let mut cmd = cmd!(sh, "git shortlog -sn");
+    if cli.email {
+        cmd = cmd.arg("-e")
+    }
+    if let Some(a) = author {
+        cmd = cmd.args(a);
+    }
+    cmd = cmd.arg(&rev_range);
+
+    let raw_shortlog = cmd.read()?;
 
     let shortlog: Vec<(usize, &str)> = raw_shortlog
         .lines()