Minor changes in query parsing for quickwit#1334. (#1356)

Quickwit's still heavily relies on generating field names
containing a '.' for nested object, yet allows for
user defined field names to contain a dot.

In order to reuse tantivy query parser, we will end up
using quickwit field names directly into tantivy.
Only '.' will be escaped.

This PR makes minor changes in how tantivy query parser parses
a field name and resolves it to a field.
Some of the new edge case behavior is hacky.

Closes #1355

query-grammar/src/query_grammar.rs

@@ -18,7 +18,7 @@ use crate::Occur;
 const SPECIAL_CHARS: &[char] = &[
     '+', '^', '`', ':', '{', '}', '"', '[', ']', '(', ')', '~', '!', '\\', '*', ' ',
 ];
-const ESCAPED_SPECIAL_CHARS_PATTERN: &str = r#"\\(\+|\^|`|:|\{|\}|"|\[|\]|\(|\)|\~|!|\\|\*| )"#;
+const ESCAPED_SPECIAL_CHARS_PATTERN: &str = r#"\\(\+|\^|`|:|\{|\}|"|\[|\]|\(|\)|\~|!|\\|\*|\s)"#;
 
 /// Parses a field_name
 /// A field name must have at least one character and be followed by a colon.
@@ -34,7 +34,8 @@ fn field_name<'a>() -> impl Parser<&'a str, Output = String> {
             take_while(|c| !SPECIAL_CHARS.contains(&c)),
         ),
         '\\',
-        satisfy(|c| SPECIAL_CHARS.contains(&c)),
+        satisfy(|_| true), /* if the next character is not a special char, the \ will be treated
+                            * as the \ character. */
     ))
     .skip(char(':'))
     .map(|s| ESCAPED_SPECIAL_CHARS_RE.replace_all(&s, "$1").to_string())
@@ -516,15 +517,27 @@ mod test {
     }
 
     #[test]
-    fn test_field_name() -> TestParseResult {
+    fn test_field_name() {
         assert_eq!(
             super::field_name().parse(".my.field.name:a"),
             Ok((".my.field.name".to_string(), "a"))
         );
+        assert_eq!(
+            super::field_name().parse(r#"my\　field:a"#),
+            Ok(("my　field".to_string(), "a"))
+        );
+        assert_eq!(
+            super::field_name().parse(r#"にんじん:a"#),
+            Ok(("にんじん".to_string(), "a"))
+        );
         assert_eq!(
             super::field_name().parse("my\\ field\\ name:a"),
             Ok(("my field name".to_string(), "a"))
         );
+        assert_eq!(
+            super::field_name().parse(r#"my\field:a"#),
+            Ok((r#"my\field"#.to_string(), "a"))
+        );
         assert!(super::field_name().parse("my field:a").is_err());
         assert_eq!(
             super::field_name().parse("\\(1\\+1\\):2"),
@@ -534,14 +547,21 @@ mod test {
             super::field_name().parse("my_field_name:a"),
             Ok(("my_field_name".to_string(), "a"))
         );
+        assert_eq!(
+            super::field_name().parse("myfield.b:hello").unwrap(),
+            ("myfield.b".to_string(), "hello")
+        );
+        assert_eq!(
+            super::field_name().parse(r#"myfield\.b:hello"#).unwrap(),
+            (r#"myfield\.b"#.to_string(), "hello")
+        );
         assert!(super::field_name().parse("my_field_name").is_err());
         assert!(super::field_name().parse(":a").is_err());
         assert!(super::field_name().parse("-my_field:a").is_err());
         assert_eq!(
-            super::field_name().parse("_my_field:a")?,
-            ("_my_field".to_string(), "a")
+            super::field_name().parse("_my_field:a"),
+            Ok(("_my_field".to_string(), "a"))
         );
-        Ok(())
     }
 
     #[test]