Add styleR for ess-r-mode (#377)

Hi! My first time adding a formatter, please let me know if I missed
anything.

Some things I'm unclear about:

1. How to fail gracefully when [styleR](https://styler.r-lib.org/)
package is absent from the system
2. Whether the formatter should be named `ess-r` or something more
general like `rlang`

## Test case

FYI, there are loads of tests to pick from on
https://github.com/r-lib/styler/tree/main/tests/testthat.

I picked
[unindention/mixed-in.R](https://github.com/r-lib/styler/blob/main/tests/testthat/unindention/mixed-in.R),
but oddly, the output
[unindention/mixed-out.R](https://github.com/r-lib/styler/blob/main/tests/testthat/unindention/mixed-out.R)
isn't quite the same as we got!

I don't know if that's an upstream issue, or that upstream changed style
since that test was written, or that perhaps the file is meant to be
concatenated into something else.

5 files changed, 32 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a0e5b83..43746aa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ The format is based on [Keep a Changelog].
 * [hurlfmt](https://hurl.dev) for hurl files.
 * [csharpier](https://github.com/belav/csharpier) for C#.
 * [taplo](https://taplo.tamasfe.dev/) for TOML.
+* [styler](https://styler.r-lib.org/) for R.
 
 ## 4.4.1 (released 2025-05-13)
 ### Enhancements
diff --git a/apheleia-formatters.el b/apheleia-formatters.el
index 581a9a1..e847716 100644
--- a/apheleia-formatters.el
+++ b/apheleia-formatters.el
@@ -174,6 +174,8 @@
     (robotidy . ("robotidy" "--no-color" "-"
                  (apheleia-formatters-indent nil "--indent")
                  (apheleia-formatters-fill-column "--line-length")))
+    (r-styler . ("R" "--no-echo" "--no-save" "--no-restore" "-e"
+                 "styler::style_text(readLines(file('stdin')))"))
     (python3-json
      . ("python3" "-m" "json.tool"
         (apheleia-formatters-indent "--tab" "--indent")))
diff --git a/test/formatters/installers/r-styler.bash b/test/formatters/installers/r-styler.bash
new file mode 100644
index 0000000..3e7f41d
--- /dev/null
+++ b/test/formatters/installers/r-styler.bash
@@ -0,0 +1,2 @@
+apt-get install -y r-base-core
+R --no-echo --no-save --no-restore -e "install.packages('styler')"
diff --git a/test/formatters/samplecode/r-styler/in.R b/test/formatters/samplecode/r-styler/in.R
new file mode 100644
index 0000000..5a00a8b
--- /dev/null
+++ b/test/formatters/samplecode/r-styler/in.R
@@ -0,0 +1,15 @@
+{
+  (((
+ 2
+    )))
+   }
+
+{
+{
+        call(
+          call1(2, 3),
+          {
+               sin(cos(pi))
+  } )
+     }
+}
diff --git a/test/formatters/samplecode/r-styler/out.R b/test/formatters/samplecode/r-styler/out.R
new file mode 100644
index 0000000..988599b
--- /dev/null
+++ b/test/formatters/samplecode/r-styler/out.R
@@ -0,0 +1,12 @@
+{
+  (((
+    2
+  )))
+}
+
+{{ call(
+  call1(2, 3),
+  {
+    sin(cos(pi))
+  }
+) }}