Make --output respect --directory

I should really add a test for this too ... but goldens are not really
suitable for this. Let's leave it untested for now then?

docs/rcl_evaluate.md

@@ -45,7 +45,10 @@ output format is `json`.
 
 ### `-o` `--output <outfile>`
 
-Write the output to the given file instead of stdout.
+Write the output to the given file instead of stdout. When [`--directory`][dir]
+is set, the output path is relative to that directory.
+
+[dir]: rcl.md#-c-directory-dir
 
 ### `--sandbox <mode>`
 

docs/rcl_format.md

@@ -29,9 +29,12 @@ exactly one input file.
 
 ### `-o` `--output <outfile>`
 
-Write the output to the given file instead of stdout. This option is
+Write the output to the given file instead of stdout. When [`--directory`][dir]
+is set, the output path is relative to that directory. This option is
 incompatible with `--in-place`.
 
+[dir]: rcl.md#-c-directory-dir
+
 ### `-w` `--width <width>`
 
 Target width in columns. Must be an integer. Defaults to 80. Note that the

src/loader.rs

@@ -50,10 +50,10 @@ pub struct PathLookup {
     /// A friendly name displayed to the user.
     ///
     /// This is the path relative to the working directory if possible.
-    name: String,
+    pub name: String,
 
     /// The absolute path on the file system to load the data from.
-    path: PathBuf,
+    pub path: PathBuf,
 }
 
 /// A filesystem resolves import paths to file contents.
@@ -328,6 +328,11 @@ impl Loader {
         Ok(())
     }
 
+    /// Resolve a path specified on the CLI so it respects the workdir.
+    pub fn resolve_cli_path(&self, path: &str) -> Result<PathLookup> {
+        self.filesystem.resolve_entrypoint(path)
+    }
+
     /// Borrow all documents.
     pub fn as_inputs(&self) -> Vec<Doc> {
         self.documents.iter().map(Document::as_doc).collect()

src/main.rs

@@ -35,11 +35,12 @@ impl App {
 
     /// Write a string to a file.
     fn print_to_file(&self, out_path: &str, data: String) -> Result<()> {
-        std::fs::write(out_path, data).map_err(|err| {
+        let out_path = self.loader.resolve_cli_path(out_path)?;
+        std::fs::write(&out_path.path, data).map_err(|err| {
             // The concat! macro is not exported, we'll make do with a vec here.
             let parts = vec![
                 "Failed to write to file '".into(),
-                Doc::highlight(out_path).into_owned(),
+                Doc::highlight(&out_path.name).into_owned(),
                 "': ".into(),
                 err.to_string().into(),
             ];