Add exception __context__

Author: palaviv

tests/snippets/try_exceptions.py

@@ -137,3 +137,8 @@ def __init__(self):
     raise
 except RuntimeError:
     pass
+
+try:
+    raise ZeroDivisionError
+except ZeroDivisionError as ex:
+    assert ex.__context__ == None

vm/src/compile.rs

@@ -572,6 +572,7 @@ impl Compiler {
         self.emit(Instruction::Jump { target: else_label });
 
         // except handlers:
+        let was_in_exc_handler = self.in_exc_handler;
         self.in_exc_handler = true;
         self.set_label(handler_label);
         // Exception is on top of stack now
@@ -609,6 +610,8 @@ impl Compiler {
 
             // Handler code:
             self.compile_statements(&handler.body)?;
+            // Drop exception from top of stack:
+            self.emit(Instruction::Pop);
             self.emit(Instruction::Jump {
                 target: finally_label,
             });
@@ -621,9 +624,6 @@ impl Compiler {
             target: handler_label,
         });
         self.set_label(handler_label);
-        // Drop exception from top of stack:
-        self.emit(Instruction::Pop);
-        self.in_exc_handler = false;
         // If code flows here, we have an unhandled exception,
         // emit finally code and raise again!
         // Duplicate finally code here:
@@ -633,8 +633,8 @@ impl Compiler {
             self.compile_statements(statements)?;
         }
         self.emit(Instruction::Raise {
-            argc: 1,
-            in_exc: false,
+            argc: 0,
+            in_exc: true,
         });
 
         // We successfully ran the try block:
@@ -649,7 +649,7 @@ impl Compiler {
         if let Some(statements) = finalbody {
             self.compile_statements(statements)?;
         }
-
+        self.in_exc_handler = was_in_exc_handler;
         // unimplemented!();
         Ok(())
     }

vm/src/frame.rs

@@ -716,23 +716,37 @@ impl Frame {
             }
 
             bytecode::Instruction::Raise { argc, in_exc } => {
-                if argc.clone() == 0 && in_exc.clone() == false {
-                    return Err(vm.new_exception(
-                        vm.ctx.exceptions.runtime_error.clone(),
-                        "No active exception to reraise".to_string(),
-                    ));
-                }
                 let cause = match argc {
                     2 => self.get_exception(vm, true)?,
                     _ => vm.get_none(),
                 };
                 let exception = match argc {
-                    0 | 1 | 2 => self.get_exception(vm, false)?,
+                    0 => match in_exc {
+                        true => self.get_exception(vm, false)?,
+                        false => {
+                            return Err(vm.new_exception(
+                                vm.ctx.exceptions.runtime_error.clone(),
+                                "No active exception to reraise".to_string(),
+                            ));
+                        }
+                    },
+                    1 | 2 => self.get_exception(vm, false)?,
                     3 => panic!("Not implemented!"),
                     _ => panic!("Invalid parameter for RAISE_VARARGS, must be between 0 to 3"),
                 };
-                info!("Exception raised: {:?} with cause: {:?}", exception, cause);
+                let context = match argc {
+                    0 => vm.get_none(), // We have already got the exception,
+                    _ => match in_exc {
+                        true => self.get_exception(vm, false)?,
+                        false => vm.get_none(),
+                    },
+                };
+                info!(
+                    "Exception raised: {:?} with cause: {:?} and context: {:?}",
+                    exception, cause, context
+                );
                 vm.set_attr(&exception, vm.new_str("__cause__".to_string()), cause)?;
+                vm.set_attr(&exception, vm.new_str("__context__".to_string()), context)?;
                 Err(exception)
             }