Add tests and cover edge cases of the :: delim.

crates/nu-parser/src/errors.rs

@@ -171,6 +171,10 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::missing_import_pattern), url(docsrs))]
     MissingImportPattern(#[label = "needs an import pattern"] Span),
 
+    #[error("Wrong import pattern structure.")]
+    #[diagnostic(code(nu::parser::missing_import_pattern), url(docsrs))]
+    WrongImportPattern(#[label = "invalid import pattern structure"] Span),
+
     #[error("Module export not found.")]
     #[diagnostic(code(nu::parser::export_not_found), url(docsrs))]
     ExportNotFound(#[label = "could not find imports"] Span),

crates/nu-parser/src/parser.rs

@@ -1711,6 +1711,33 @@ pub fn parse_import_pattern(
         );
     }
 
+    if (tokens.len() != 1) && (tokens.len() != 4) {
+        return (
+            ImportPattern {
+                head: vec![],
+                members: vec![],
+            },
+            Some(ParseError::WrongImportPattern(span)),
+        );
+    }
+
+    let has_second_colon = if let Some(t) = tokens.get(2) {
+        let potential_colon = working_set.get_span_contents(t.span);
+        potential_colon == b":"
+    } else {
+        false
+    };
+
+    if (tokens.len() == 4) && !has_second_colon {
+        return (
+            ImportPattern {
+                head: vec![],
+                members: vec![],
+            },
+            Some(ParseError::WrongImportPattern(span)),
+        );
+    }
+
     let head = working_set.get_span_contents(tokens[0].span).to_vec();
 
     if let Some(tail) = tokens.get(3) {