Avoid F821 false-positives with NameError (#386)

src/ast/helpers.rs

@@ -1,6 +1,6 @@
 use once_cell::sync::Lazy;
 use regex::Regex;
-use rustpython_ast::{Expr, ExprKind, StmtKind};
+use rustpython_ast::{Excepthandler, ExcepthandlerKind, Expr, ExprKind, StmtKind};
 
 use crate::python::typing;
 
@@ -35,6 +35,22 @@ pub fn match_annotated_subscript(expr: &Expr) -> Option<SubscriptKind> {
     }
 }
 
+fn node_name(expr: &Expr) -> Option<&str> {
+    if let ExprKind::Name { id, .. } = &expr.node {
+        Some(id)
+    } else {
+        None
+    }
+}
+
+pub fn match_name_or_attr(expr: &Expr, target: &str) -> bool {
+    match &expr.node {
+        ExprKind::Attribute { attr, .. } => target == attr,
+        ExprKind::Name { id, .. } => target == id,
+        _ => false,
+    }
+}
+
 pub fn is_assignment_to_a_dunder(node: &StmtKind) -> bool {
     // Check whether it's an assignment to a dunder, with or without a type annotation.
     // This is what pycodestyle (as of 2.9.1) does.
@@ -65,10 +81,27 @@ pub fn is_assignment_to_a_dunder(node: &StmtKind) -> bool {
     }
 }
 
-pub fn match_name_or_attr(expr: &Expr, target: &str) -> bool {
-    match &expr.node {
-        ExprKind::Attribute { attr, .. } => target == attr,
-        ExprKind::Name { id, .. } => target == id,
-        _ => false,
+/// Extract the names of all handled exceptions.
+/// Note that, for now, this only matches on ExprKind::Name, and so won't catch exceptions like
+/// `module.CustomException`. (But will catch all builtin exceptions.)
+pub fn extract_handler_names(handlers: &[Excepthandler]) -> Vec<&str> {
+    let mut handler_names = vec![];
+    for handler in handlers {
+        match &handler.node {
+            ExcepthandlerKind::ExceptHandler { type_, .. } => {
+                if let Some(type_) = type_ {
+                    if let ExprKind::Tuple { elts, .. } = &type_.node {
+                        for type_ in elts {
+                            if let Some(name) = node_name(type_) {
+                                handler_names.push(name);
+                            }
+                        }
+                    } else if let Some(name) = node_name(type_) {
+                        handler_names.push(name);
+                    }
+                }
+            }
+        }
     }
+    handler_names
 }