Improve handling of named pipe arguments

Use display_name in more places, and prefer file names with extensions
when we have two arguments.

Fixes #783

CHANGELOG.md

@@ -6,6 +6,10 @@ Improved handling of multiline strings, which could cause a crash if
 they occurred at the end of the file. This was particularly noticeable
 with YAML.
 
+### Parsing
+
+Improved language detection when one argument is a named pipe.
+
 ### Syntax Highlighting
 
 Improved syntax highlighting, particularly for keywords.

src/main.rs

@@ -546,13 +546,12 @@ fn diff_file_content(
     diff_options: &DiffOptions,
     overrides: &[(LanguageOverride, Vec<glob::Pattern>)],
 ) -> DiffResult {
-    let (guess_src, guess_path) = match rhs_path {
+    let guess_src = match rhs_path {
-        FileArgument::NamedPath(path) => (&rhs_src, Path::new(path)),
+        FileArgument::DevNull => &lhs_src,
-        FileArgument::Stdin => (&rhs_src, Path::new(&display_path)),
+        _ => &rhs_src,
-        FileArgument::DevNull => (&lhs_src, Path::new(&display_path)),
     };
 
-    let language = guess(guess_path, guess_src, overrides);
+    let language = guess(Path::new(display_path), guess_src, overrides);
     let lang_config = language.map(|lang| (lang, tsp::from_language(lang)));
 
     if lhs_src == rhs_src {

src/options.rs

@@ -556,7 +556,13 @@ fn build_display_path(lhs_path: &FileArgument, rhs_path: &FileArgument) -> Strin
 
             match common_path_suffix(lhs, rhs) {
                 Some(common_suffix) => common_suffix,
-                None => rhs.display().to_string(),
+                None => {
+                    if rhs.extension().is_some() {
+                        rhs.display().to_string()
+                    } else {
+                        lhs.display().to_string()
+                    }
+                }
             }
         }
         (FileArgument::NamedPath(p), _) | (_, FileArgument::NamedPath(p)) => {