Fix F841 (UnusedVariable) range in except handler (#1367)

src/ast/helpers.rs

@@ -1,3 +1,4 @@
+use itertools::Itertools;
 use log::error;
 use once_cell::sync::Lazy;
 use regex::Regex;
@@ -396,6 +397,23 @@ pub fn identifier_range(stmt: &Stmt, locator: &SourceCodeLocator) -> Range {
     Range::from_located(stmt)
 }
 
+/// Return the `Range` of `name` in `Excepthandler`.
+pub fn excepthandler_name_range(
+    handler: &Excepthandler,
+    locator: &SourceCodeLocator,
+) -> Option<Range> {
+    let contents = locator.slice_source_code_range(&Range::from_located(handler));
+    let range = lexer::make_tokenizer(&contents)
+        .flatten()
+        .tuple_windows()
+        .find(|(tok, next_tok)| matches!(tok.1, Tok::As) && matches!(next_tok.1, Tok::Name { .. }))
+        .map(|((..), (start, _, end))| Range {
+            location: to_absolute(start, handler.location),
+            end_location: to_absolute(end, handler.location),
+        });
+    range
+}
+
 /// Return `true` if a `Stmt` appears to be part of a multi-statement line, with
 /// other statements preceding it.
 pub fn preceded_by_continuation(stmt: &Stmt, locator: &SourceCodeLocator) -> bool {