fix(json): proper escapes for JSON strings (#101)

Includes two fixes:
1. Things like `\n` are not doubly-escaped any more
2. The backslash `\` itself in the source is escaped

src/handlers/json.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use std::fmt::{self, Write};
 
 use crate::{protocol::Diagnostic, ReportHandler, Severity};
 
@@ -23,20 +23,34 @@ impl Default for JSONReportHandler {
     }
 }
 
-fn escape(input: &str) -> String {
-    input
-        .chars()
-        .map(|c| match c {
-            '"' => "\\\\\"".to_string(),
-            '\'' => "\\\\'".to_string(),
-            '\r' => "\\\\r".to_string(),
-            '\n' => "\\\\n".to_string(),
-            '\t' => "\\\\t".to_string(),
-            '\u{08}' => "\\\\b".to_string(),
-            '\u{0c}' => "\\\\f".to_string(),
-            c => format!("{}", c),
-        })
-        .collect()
+struct Escape<'a>(&'a str);
+
+impl fmt::Display for Escape<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        for c in self.0.chars() {
+            let escape = match c {
+                '\\' => Some(r"\\"),
+                '"' => Some(r#"\""#),
+                '\'' => Some(r"\'"),
+                '\r' => Some(r"\r"),
+                '\n' => Some(r"\n"),
+                '\t' => Some(r"\t"),
+                '\u{08}' => Some(r"\b"),
+                '\u{0c}' => Some(r"\f"),
+                _ => None,
+            };
+            if let Some(escape) = escape {
+                f.write_str(escape)?;
+            } else {
+                f.write_char(c)?;
+            }
+        }
+        Ok(())
+    }
+}
+
+fn escape(input: &'_ str) -> Escape<'_> {
+    Escape(input)
 }
 
 impl JSONReportHandler {
@@ -93,7 +107,13 @@ impl JSONReportHandler {
         }
         if let Some(relateds) = diagnostic.related() {
             write!(f, r#""related": ["#)?;
+            let mut add_comma = false;
             for related in relateds {
+                if add_comma {
+                    write!(f, ",")?;
+                } else {
+                    add_comma = true;
+                }
                 self.render_report(f, related)?;
             }
             write!(f, "]")?;
@@ -127,3 +147,9 @@ impl ReportHandler for JSONReportHandler {
         self.render_report(f, diagnostic)
     }
 }
+
+#[test]
+fn test_escape() {
+    assert_eq!(escape("a\nb").to_string(), r"a\nb");
+    assert_eq!(escape("C:\\Miette").to_string(), r"C:\\Miette");
+}

tests/test_json.rs

@@ -497,7 +497,7 @@ mod json_report_handler {
         println!("Error: {}", out);
         let expected: String = r#"
         {
-            "message": "wtf?!\\nit broke :(",
+            "message": "wtf?!\nit broke :(",
             "code": "oops::my::bad",
             "severity": "error",
             "help": "try doing it better next time?",
@@ -737,11 +737,18 @@ mod json_report_handler {
         let err = MyBad {
             src: NamedSource::new("bad_file.rs", src.clone()),
             highlight: (9, 4).into(),
-            related: vec![MyBad {
-                src: NamedSource::new("bad_file2.rs", src),
-                highlight: (0, 6).into(),
-                related: vec![],
-            }],
+            related: vec![
+                MyBad {
+                    src: NamedSource::new("bad_file2.rs", src.clone()),
+                    highlight: (0, 6).into(),
+                    related: vec![],
+                },
+                MyBad {
+                    src: NamedSource::new("bad_file3.rs", src),
+                    highlight: (0, 6).into(),
+                    related: vec![],
+                },
+            ],
         };
         let out = fmt_report(err.into());
         println!("Error: {}", out);
@@ -777,6 +784,22 @@ mod json_report_handler {
                     }
                 ],
                 "related": []
+            },{
+                "message": "oops!",
+                "code": "oops::my::bad",
+                "severity": "error",
+                "help": "try doing it better next time?",
+                "filename": "bad_file3.rs",
+                "labels": [
+                    {
+                        "label": "this bit here",
+                        "span": {
+                            "offset": 0,
+                            "length": 6
+                        }
+                    }
+                ],
+                "related": []
             }]
         }"#
         .lines()