Implement Py38 named expression (PEP 572) (#1934)

* Initial implementation of named expression and  import  according CPython tests

* added new instruction with inversed evaluation order for dict comprehension, in other cases use regular evaluation order

* added further aspects to implementation, cleaned up, imported test from CPython

* implemented first parts of scoping enhancement and extended checks

* completion of name resolution ongoing, now more test passing, still warinings and cleanup required

* further optimization of name resolution in nested scopes

* Initialize the vm with imports from _io instead of io

* Add the OpenBSD support that I am smart enough to

* adapted grammer to full support, most test are passing now, esp. all invalids are passed. Cleaned up in symboltable

* more conditional compiling, this time for errors

* rustfmt was not pleased

* premature push, whoops

* Add expected_failure result type to jsontests

* Initial implementation of named expression and  import  according CPython tests

* added new instruction with inversed evaluation order for dict comprehension, in other cases use regular evaluation order

* added further aspects to implementation, cleaned up, imported test from CPython

* implemented first parts of scoping enhancement and extended checks

* completion of name resolution ongoing, now more test passing, still warinings and cleanup required

* further optimization of name resolution in nested scopes

* adapted grammer to full support, most test are passing now, esp. all invalids are passed. Cleaned up in symboltable

* Fixed nameing convention violation and removed unnecessary information from symbol resolution. Added some more comments.

* Fixed nameing convention violation and removed unnecessary information from symbol resolution. Added some more comments.

Co-authored-by: Noah <33094578+coolreader18@users.noreply.github.com>
Co-authored-by: Reuben Staley <lighthousemaniac@gmail.com>

bytecode/src/bytecode.rs

@@ -273,6 +273,7 @@ pub enum Instruction {
     MapAdd {
         i: usize,
     },
+
     PrintExpr,
     LoadBuildClass,
     UnpackSequence {
@@ -296,6 +297,13 @@ pub enum Instruction {
     },
     GetAIter,
     GetANext,
+
+    /// Reverse order evaluation in MapAdd
+    /// required to support named expressions of Python 3.8 in dict comprehension
+    /// today (including Py3.9) only required in dict comprehension.
+    MapAddRev {
+        i: usize,
+    },
 }
 
 use self::Instruction::*;
@@ -586,7 +594,7 @@ impl Instruction {
             BuildSlice { size } => w!(BuildSlice, size),
             ListAppend { i } => w!(ListAppend, i),
             SetAdd { i } => w!(SetAdd, i),
-            MapAdd { i } => w!(MapAdd, i),
+            MapAddRev { i } => w!(MapAddRev, i),
             PrintExpr => w!(PrintExpr),
             LoadBuildClass => w!(LoadBuildClass),
             UnpackSequence { size } => w!(UnpackSequence, size),
@@ -597,6 +605,7 @@ impl Instruction {
             GetAwaitable => w!(GetAwaitable),
             GetAIter => w!(GetAIter),
             GetANext => w!(GetANext),
+            MapAdd { i } => w!(MapAdd, i),
         }
     }
 }