Fix json string escape

src/grammar.pest

@@ -15,7 +15,13 @@ literal = { string_literal |
 null_literal = @{ "null" ~ !symbol_char }
 boolean_literal = @{ ("true"|"false") ~ !symbol_char }
 number_literal = @{ "-"? ~ ASCII_DIGIT+ ~ "."? ~ ASCII_DIGIT* ~ ("E" ~ "-"? ~ ASCII_DIGIT+)? }
-string_literal = @{ ("\"" ~ (!"\"" ~ ("\\\"" | ANY))* ~ "\"") | ("'" ~ (!"'" ~ ("\\'" | ANY))* ~ "'") }
+json_char = {
+    !("\"" | "\\") ~ ANY
+    | "\\" ~ ("\"" | "\\" | "/" | "b" | "f" | "n" | "r" | "t")
+    | "\\" ~ ("u" ~ ASCII_HEX_DIGIT{4})
+}
+string_inner = @{ json_char* }
+string_literal = ${ "\"" ~ string_inner ~ "\"" }
 array_literal = { "[" ~ literal? ~ ("," ~ literal)* ~ "]" }
 object_literal = { "{" ~ (string_literal ~ ":" ~ literal)?
                    ~ ("," ~ string_literal ~ ":" ~ literal)* ~ "}" }

src/grammar.rs

@@ -125,8 +125,6 @@ mod test {
         let s = vec![
             "\"json string\"",
             "\"quot: \\\"\"",
-            "'json string'",
-            "'quot: \\''",
             "[]",
             "[\"hello\"]",
             "[1,2,3,4,true]",
@@ -174,6 +172,7 @@ mod test {
             "{{exp 1}}",
             "{{exp \"literal\"}}",
             "{{exp \"literal with space\"}}",
+            r#"{{exp "literal with escape \\\\"}}"#,
             "{{exp ref}}",
             "{{exp (sub)}}",
             "{{exp (sub 123)}}",

src/lib.rs

@@ -358,7 +358,7 @@
 //!
 //!
 
-#![allow(dead_code)]
+#![allow(dead_code, clippy::upper_case_acronyms)]
 #![warn(rust_2018_idioms)]
 #![recursion_limit = "200"]
 

tests/escape.rs

@@ -3,7 +3,7 @@ extern crate handlebars;
 #[macro_use]
 extern crate serde_json;
 
-use handlebars::Handlebars;
+use handlebars::{handlebars_helper, Handlebars};
 
 #[test]
 fn test_escape_216() {
@@ -19,3 +19,25 @@ fn test_escape_216() {
         r"\\\\ foo bar foobar foo#bar foo//bar foo\foo foo\\\foo\\foo \\foo {{FOO}} {{FOO}}"
     );
 }
+
+#[test]
+fn test_string_no_escape_422() {
+    let mut hbs = Handlebars::new();
+
+    handlebars_helper!(replace: |input: str, from: str, to: str| {
+        input.replace(from, to)
+    });
+    hbs.register_helper("replace", Box::new(replace));
+
+    assert_eq!(
+        r#"some\ path"#,
+        hbs.render_template(r#"{{replace "some/path" "/" "\\ " }}"#, &())
+            .unwrap()
+    );
+
+    assert_eq!(
+        r#"some\path"#,
+        hbs.render_template(r#"{{replace "some/path" "/" "\\" }}"#, &())
+            .unwrap()
+    );
+}