Merge pull request RustPython#1305 from RustPython/fix-try-else

Repair try-except-else syntax. Fixes RustPython#1300.

Author: palaviv

parser/src/ast.rs

@@ -24,7 +24,7 @@ pub enum Top {
 
 #[derive(Debug, PartialEq)]
 pub struct Program {
-    pub statements: Vec<Statement>,
+    pub statements: Suite,
 }
 
 #[derive(Debug, PartialEq)]
@@ -40,6 +40,7 @@ pub struct Located<T> {
 }
 
 pub type Statement = Located<StatementType>;
+pub type Suite = Vec<Statement>;
 
 /// Abstract syntax tree nodes for python statements.
 #[derive(Debug, PartialEq)]
@@ -90,39 +91,39 @@ pub enum StatementType {
     },
     If {
         test: Expression,
-        body: Vec<Statement>,
-        orelse: Option<Vec<Statement>>,
+        body: Suite,
+        orelse: Option<Suite>,
     },
     While {
         test: Expression,
-        body: Vec<Statement>,
-        orelse: Option<Vec<Statement>>,
+        body: Suite,
+        orelse: Option<Suite>,
     },
     With {
         is_async: bool,
         items: Vec<WithItem>,
-        body: Vec<Statement>,
+        body: Suite,
     },
     For {
         is_async: bool,
         target: Box<Expression>,
         iter: Box<Expression>,
-        body: Vec<Statement>,
-        orelse: Option<Vec<Statement>>,
+        body: Suite,
+        orelse: Option<Suite>,
     },
     Raise {
         exception: Option<Expression>,
         cause: Option<Expression>,
     },
     Try {
-        body: Vec<Statement>,
+        body: Suite,
         handlers: Vec<ExceptHandler>,
-        orelse: Option<Vec<Statement>>,
-        finalbody: Option<Vec<Statement>>,
+        orelse: Option<Suite>,
+        finalbody: Option<Suite>,
     },
     ClassDef {
         name: String,
-        body: Vec<Statement>,
+        body: Suite,
         bases: Vec<Expression>,
         keywords: Vec<Keyword>,
         decorator_list: Vec<Expression>,
@@ -131,7 +132,7 @@ pub enum StatementType {
         is_async: bool,
         name: String,
         args: Box<Parameters>,
-        body: Vec<Statement>,
+        body: Suite,
         decorator_list: Vec<Expression>,
         returns: Option<Expression>,
     },
@@ -331,7 +332,7 @@ pub struct ExceptHandler {
     pub location: Location,
     pub typ: Option<Expression>,
     pub name: Option<String>,
-    pub body: Vec<Statement>,
+    pub body: Suite,
 }
 
 #[derive(Debug, PartialEq)]

parser/src/python.lalrpop

@@ -31,22 +31,22 @@ Program: ast::Program = {
 };
 
 // A file line either has a declaration, or an empty newline:
-FileLine: Vec<ast::Statement> = {
+FileLine: ast::Suite = {
     Statement,
     "\n" => vec![],
 };
 
-Suite: Vec<ast::Statement> = {
+Suite: ast::Suite = {
     SimpleStatement,
     "\n" indent <s:Statement+> dedent => s.into_iter().flatten().collect(),
 };
 
-Statement: Vec<ast::Statement> = {
+Statement: ast::Suite = {
     SimpleStatement,
     <s:CompoundStatement> => vec![s],
 };
 
-SimpleStatement: Vec<ast::Statement> = {
+SimpleStatement: ast::Suite = {
     <s1:SmallStatement> <s2:(";" SmallStatement)*> ";"? "\n" => {
         let mut statements = vec![s1];
         statements.extend(s2.into_iter().map(|e| e.1));
@@ -365,7 +365,7 @@ ForStatement: ast::Statement = {
 };
 
 TryStatement: ast::Statement = {
-    <location:@L> "try" ":" <body:Suite> <handlers:ExceptClause*> <else_suite:("else" ":" Suite)?> <finally:("finally" ":" Suite)?> => {
+    <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 {
@@ -378,6 +378,20 @@ TryStatement: ast::Statement = {
             },
         }
     },
+    <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,
+            },
+        }
+    },
 };
 
 ExceptClause: ast::ExceptHandler = {

tests/snippets/try_exceptions.py

@@ -238,3 +238,21 @@ def y():
         raise NameError from ex
 except NameError as ex2:
     pass
+
+
+# the else clause requires at least one except clause:
+with assertRaises(SyntaxError):
+    exec("""
+try:
+    pass
+else:
+    pass
+    """)
+
+
+# Try requires at least except or finally (or both)
+with assertRaises(SyntaxError):
+    exec("""
+try:
+    pass
+""")