Standardize path formatting

src/error.rs

@@ -1,4 +1,4 @@
-use crate::format::CodeStr;
+use crate::format::CodePath;
 use colored::{Colorize, control::SHOULD_COLORIZE};
 use std::{
     cmp::{max, min},
@@ -50,14 +50,14 @@ pub fn throw<T: error::Error + 'static>(
                     format!(
                         "{} {} {}",
                         "[Error]".red().bold(),
-                        format!("[{}]", path.to_string_lossy().code_str()).magenta(),
+                        format!("[{}]", path.code_path()).magenta(),
                         message,
                     )
                 } else {
                     format!(
                         "{} {} {}\n\n{}",
                         "[Error]".red().bold(),
-                        format!("[{}]", path.to_string_lossy().code_str()).magenta(),
+                        format!("[{}]", path.code_path()).magenta(),
                         message,
                         listing,
                     )
@@ -66,7 +66,7 @@ pub fn throw<T: error::Error + 'static>(
                 format!(
                     "{} {} {}",
                     "[Error]".red().bold(),
-                    format!("[{}]", path.to_string_lossy().code_str()).magenta(),
+                    format!("[{}]", path.code_path()).magenta(),
                     message,
                 )
             }

src/format.rs

@@ -1,4 +1,16 @@
 use colored::{ColoredString, Colorize, control::SHOULD_COLORIZE};
+use std::path::Path;
+
+// This trait formats a filesystem path for human-facing diagnostic output.
+pub trait CodePath {
+    fn code_path(&self) -> ColoredString;
+}
+
+impl CodePath for Path {
+    fn code_path(&self) -> ColoredString {
+        self.to_string_lossy().code_str()
+    }
+}
 
 // This trait has a function for formatting "code-like" text, such as a file path. The reason it's
 // implemented as a trait and not just a function is so we can use it with method syntax, as in

src/main.rs

@@ -15,7 +15,7 @@ mod unifier;
 use crate::{
     error::{Error, throw},
     evaluator::evaluate,
-    format::CodeStr,
+    format::{CodePath, CodeStr},
     parser::parse,
     tokenizer::tokenize,
     type_checker::type_check,
@@ -124,10 +124,7 @@ fn run(source_path: &Path, check_only: bool) -> Result<(), Error> {
     // Read the file.
     let source_contents = read_to_string(source_path).map_err(|error| {
         throw(
-            &format!(
-                "Error when reading file {}.",
-                source_path.to_string_lossy().code_str(),
-            ),
+            &format!("Error when reading file {}.", source_path.code_path()),
             None,
             None,
             Some(error),

src/parser.rs

@@ -1,7 +1,7 @@
 use crate::{
     error::{Error, SourceRange, listing, throw},
     evaluator::is_value,
-    format::CodeStr,
+    format::{CodePath, CodeStr},
     term,
     term::free_variables,
     token::{self, TerminatorType, Token},
@@ -3748,7 +3748,7 @@ fn parse_group<'a>(
                                 "{} {} This parenthesis was never closed:\n\n{}\n\nIt was \
                                     expected to be closed at the end of this line:\n\n{}",
                                 "[Error]".red().bold(),
-                                format!("[{}]", path.to_string_lossy().code_str()).magenta(),
+                                format!("[{}]", path.code_path()).magenta(),
                                 left_parenthesis_listing,
                                 unexpected_token_listing,
                             )
@@ -3766,7 +3766,7 @@ fn parse_group<'a>(
                             "{} {} This parenthesis was never closed:\n\n{}\n\nIt was \
                                 expected to be closed before {}:\n\n{}",
                             "[Error]".red().bold(),
-                            format!("[{}]", path.to_string_lossy().code_str()).magenta(),
+                            format!("[{}]", path.code_path()).magenta(),
                             left_parenthesis_listing,
                             tokens[next].to_string().code_str(),
                             unexpected_token_listing,