From 19112cef493d0fbf6a80eb286ca680c4fe0034b7 Mon Sep 17 00:00:00 2001
From: Windel Bouwman <windel@windel.nl>
Date: Mon, 19 Aug 2019 09:00:08 +0200
Subject: [PATCH] Require at least finally or except on a try statement.

---
 parser/src/python.lalrpop        | 23 +++++++++++++++--------
 tests/snippets/try_exceptions.py | 19 ++++++++++++++-----
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/parser/src/python.lalrpop b/parser/src/python.lalrpop
index f6ac629bc..2ee1e90d9 100644
--- a/parser/src/python.lalrpop
+++ b/parser/src/python.lalrpop
@@ -365,8 +365,8 @@ ForStatement: ast::Statement = {
 };
 
 TryStatement: ast::Statement = {
-    <location:@L> "try" ":" <body:Suite> <handlers:ExceptionHandlers?> <finally:("finally" ":" Suite)?> => {
-        let (handlers, orelse) = handlers.unwrap_or_default();
+    <location:@L> "try" ":" <body:Suite> <handlers:ExceptClause+> <else_suite:("else" ":" Suite)?> <finally:("finally" ":" Suite)?> => {
+        let orelse = else_suite.map(|s| s.2);
         let finalbody = finally.map(|s| s.2);
         ast::Statement {
             location,
@@ -378,12 +378,19 @@ TryStatement: ast::Statement = {
             },
         }
     },
-};
-
-ExceptionHandlers: (Vec<ast::ExceptHandler>, Option<ast::Suite>) = {
-    <handlers:ExceptClause+> <else_suite:("else" ":" Suite)?> => {
-        let orelse = else_suite.map(|s| s.2);
-        (handlers, orelse)
+    <location:@L> "try" ":" <body:Suite> <finally:("finally" ":" Suite)> => {
+        let handlers = vec![];
+        let orelse = None;
+        let finalbody = Some(finally.2);
+        ast::Statement {
+            location,
+            node: ast::StatementType::Try {
+                body,
+                handlers,
+                orelse,
+                finalbody,
+            },
+        }
     },
 };
 
diff --git a/tests/snippets/try_exceptions.py b/tests/snippets/try_exceptions.py
index 40100cb72..9ff56da77 100644
--- a/tests/snippets/try_exceptions.py
+++ b/tests/snippets/try_exceptions.py
@@ -240,10 +240,19 @@ except NameError as ex2:
     pass
 
 
+# the else clause requires at least one except clause:
 with assertRaises(SyntaxError):
-    exec("""if True:
-    try:
-        pass
-    else:
-        pass
+    exec("""
+try:
+    pass
+else:
+    pass
     """)
+
+
+# Try requires at least except or finally (or both)
+with assertRaises(SyntaxError):
+    exec("""
+try:
+    pass
+""")