fix(vrl): update unquoted allowed-characters (#14114)

lib/lookup/src/field.rs

@@ -2,7 +2,7 @@ use once_cell::sync::Lazy;
 use regex::Regex;
 
 static VALID_FIELD: Lazy<Regex> =
-    Lazy::new(|| Regex::new("^[0-9]*[a-zA-Z_][0-9a-zA-Z_]*$").unwrap());
+    Lazy::new(|| Regex::new("^[0-9]*[a-zA-Z_@][0-9a-zA-Z_@]*$").unwrap());
 
 /// A valid fieldname can contain alphanumeric characters and an underscore.
 /// It may start with a number, but has to consist of more than just a number.

lib/lookup/src/path.lalrpop

@@ -25,7 +25,7 @@ PathSegment: Segment<'input> = {
 }
 
 Field: Field<'input> = {
-   <s:r"[0-9]*[a-zA-Z_][0-9a-zA-Z_]*"> => Field::from(s),
+   <s:r"[0-9]*[a-zA-Z_@][0-9a-zA-Z_@]*"> => Field::from(s),
    <s:r#""(\\"|[^"])+""#> => Field::from(s),
 }
 

lib/vrl/compiler/src/expression/assignment.rs

@@ -228,10 +228,10 @@ fn verify_overwriteable(
         let (variant, segment_span, valid) = match last {
             segment @ (SegmentBuf::Field(_) | SegmentBuf::Coalesce(_)) => {
                 let segment_str = segment.to_string();
-                let segment_start = parent_span.end() - segment_str.len();
+                let segment_start = parent_span.end().saturating_sub(segment_str.len());
                 let segment_span = Span::new(segment_start, parent_span.end());
 
-                parent_span = Span::new(parent_span.start(), segment_start - 1);
+                parent_span = Span::new(parent_span.start(), segment_start.saturating_sub(1));
                 remainder_str.insert_str(0, &format!(".{}", segment_str));
 
                 ("object", segment_span, parent_kind.contains_object())

lib/vrl/tests/tests/issues/13461/1.vrl

@@ -0,0 +1,2 @@
+# result: true
+.(a|b) = true

lib/vrl/tests/tests/issues/13461/2.vrl

@@ -0,0 +1,2 @@
+# result: true
+.("a b" | c) = true

lib/vrl/tests/tests/issues/13461/3.vrl

@@ -0,0 +1,2 @@
+# result: true
+."foo @bar".baz = true

lib/vrl/tests/tests/issues/13461/4.vrl

@@ -0,0 +1,2 @@
+# result: true
+.@@foo = true

lib/vrl/tests/tests/issues/13461/5.vrl

@@ -0,0 +1,2 @@
+# result: true
+.@foo = true

lib/vrl/tests/tests/issues/13461/6.vrl

@@ -0,0 +1,2 @@
+# result: true
+."$foo" = true