Add support for `treefmt` (#280)

This formatter is formatting via
[treefmt](https://numtide.github.io/treefmt). This is useful if the
project is configuring formatters for the project and you don't have to
replicate this logic within Emacs, but instead utilize treefmt directly.

To do that you can set the `apheleia-formatter` to `treefmt` within the
projects `.dir-locals.el`.

I noticed there are tests for this, since treefmt could technically
format anything, I went with treefmt formatting rust code. It also
relies on having a `treefmt.toml` in the project folder, so had to add
that as well in the tests.

3 files changed, 32 insertions, 0 deletions

diff --git a/test/formatters/installers/treefmt.bash b/test/formatters/installers/treefmt.bash
new file mode 100644
index 0000000..ac42f01
--- /dev/null
+++ b/test/formatters/installers/treefmt.bash
@@ -0,0 +1,11 @@
+ver="$(latest_release numtide/treefmt)"
+
+wget "https://github.com/numtide/treefmt/releases/download/${ver}/treefmt-x86_64-unknown-linux-gnu.tar.gz" -O - | tar -C /usr/local/bin -xz
+chmod +x /usr/local/bin/treefmt
+
+apt-get install -y rustfmt
+cat <<EOT >> /tmp/treefmt.toml
+[formatter.rust]
+command = "rustfmt"
+includes = ["*.rs"]
+EOT
diff --git a/test/formatters/samplecode/treefmt/in.rs b/test/formatters/samplecode/treefmt/in.rs
new file mode 100644
index 0000000..e09c014
--- /dev/null
+++ b/test/formatters/samplecode/treefmt/in.rs
@@ -0,0 +1,12 @@
+fn foo() {
+    println!("a");
+}
+
+
+
+fn bar() {
+    println!("b");
+
+
+    println!("c");
+}
diff --git a/test/formatters/samplecode/treefmt/out.rs b/test/formatters/samplecode/treefmt/out.rs
new file mode 100644
index 0000000..28db64c
--- /dev/null
+++ b/test/formatters/samplecode/treefmt/out.rs
@@ -0,0 +1,9 @@
+fn foo() {
+    println!("a");
+}
+
+fn bar() {
+    println!("b");
+
+    println!("c");
+}