Add initial enamldef const storage

enaml/core/block_compiler.py

@@ -111,6 +111,10 @@ def visit_StorageExpr(self, node):
         # Grab the index of the parent node for later use.
         self.aux_index_map[node] = self.parent_index()
 
+    def visit_ConstExpr(self, node):
+        # Grab the index of the parent node for later use.
+        self.aux_index_map[node] = self.parent_index()
+
     def visit_FuncDef(self, node):
         # Grab the index of the parent node for later use.
         self.aux_index_map[node] = self.parent_index()
@@ -180,6 +184,12 @@ def visit_StorageExpr(self, node):
         if node.expr is not None:
             cmn.gen_operator_binding(cg, node.expr, index, node.name)
 
+    def visit_ConstExpr(self, node):
+        # Generate the code for the const expression.
+        cg = self.code_generator
+        index = self.parent_index()
+        cmn.gen_const_expr(cg, node, index, self.local_names)
+
     def visit_FuncDef(self, node):
         # Generate the code for the function declaration.
         cg = self.code_generator

enaml/core/compiler_common.py

@@ -862,6 +862,61 @@ def gen_storage_expr(cg, node, index, local_names):
         cg.pop_top()
 
 
+def gen_const_expr(cg, node, index, local_names):
+    """ Generate the code for a const expression.
+
+    The caller should ensure that NODE_LIST is present in the fast
+    locals of the code object.
+
+    Parameters
+    ----------
+    cg : CodeGenerator
+        The code generator with which to write the code.
+
+    node : ConstExpr
+        The enaml ast node of interest.
+
+    index : int
+        The index of the target node in the node list.
+
+    local_names : set
+        The set of fast local names available to the code object.
+
+    """
+    with cg.try_squash_raise():
+        cg.set_lineno(node.lineno)
+        if PY311:
+            cg.push_null()
+        load_helper(cg, 'add_storage')
+        load_node(cg, index)
+        cg.load_const(node.name)
+        if node.typename:
+            load_typename(cg, node.typename, local_names)
+        else:
+            cg.load_const(None)
+        cg.load_const("const")
+        cg.call_function(4)
+        cg.pop_top()
+
+    # Generate the operator
+    code = sanitize_operator_code(cg.filename, 'eval', node.expr.ast)
+    with cg.try_squash_raise():
+        cg.set_lineno(node.lineno)
+        if PY311:
+            cg.push_null()
+        load_helper(cg, 'run_operator')
+        load_node(cg, index)
+        # For operators not in a template instance the scope_node and the node
+        # are one and the same hence the dup_top.
+        cg.dup_top()
+        cg.load_const(node.name)
+        cg.load_const("=")
+        cg.load_const(code)
+        cg.load_fast(F_GLOBALS)
+        cg.call_function(6)
+        cg.pop_top()
+
+
 def _insert_decl_function(cg, funcdef):
     """ Create and place a declarative function on the TOS.
 

enaml/core/compiler_helpers.py

@@ -7,7 +7,7 @@
 #------------------------------------------------------------------------------
 from functools import update_wrapper
 
-from atom.api import Event, Instance, Member, add_member
+from atom.api import Event, Instance, Member, ReadOnly, add_member
 from atom.datastructures.api import sortedmap
 
 from .alias import Alias
@@ -125,7 +125,7 @@ def add_storage(node, name, store_type, kind):
     store_type : type or None
         The type of values to allow on the attribute.
 
-    kind : 'attr' or 'event'
+    kind : 'attr', 'event', or 'const'
         The kind of storage to add to the class.
 
     """
@@ -151,6 +151,8 @@ def add_storage(node, name, store_type, kind):
         new = d_(Event(store_type), writable=False, final=False)
     elif kind == 'attr':
         new = d_(Instance(store_type), final=False)
+    elif kind == 'const':
+        new = d_(ReadOnly(store_type), final=False)
     else:
         raise RuntimeError("invalid kind '%s'" % kind)
 

enaml/core/parser/enaml.gram

@@ -164,6 +164,7 @@ child_def_simple_item:
     | ex_binding
     | alias_expr
     | storage_expr
+    | const_expr
     | 'pass' NEWLINE { ast.Pass(LOCATIONS) }
 
 # --- Binding --------------------------------------------------------------------------

enaml/core/parser/enaml_parser.py

@@ -21,8 +21,6 @@
 Load = ast.Load()
 Store = ast.Store()
 Del = ast.Del()
-
-
 # Keywords and soft keywords are listed at the end of the parser definition.
 class EnamlParser(Parser):
     @memoize
@@ -416,7 +414,7 @@ def child_def_item(self) -> Optional[Any]:
 
     @memoize
     def child_def_simple_item(self) -> Optional[Any]:
-        # child_def_simple_item: binding | ex_binding | alias_expr | storage_expr | 'pass' NEWLINE
+        # child_def_simple_item: binding | ex_binding | alias_expr | storage_expr | const_expr | 'pass' NEWLINE
         mark = self._mark()
         tok = self._tokenizer.peek()
         start_lineno, start_col_offset = tok.start
@@ -432,6 +430,9 @@ def child_def_simple_item(self) -> Optional[Any]:
         if storage_expr := self.storage_expr():
             return storage_expr
         self._reset(mark)
+        if const_expr := self.const_expr():
+            return const_expr
+        self._reset(mark)
         if (self.expect("pass")) and (self.expect("NEWLINE")):
             tok = self._tokenizer.get_last_non_whitespace_token()
             end_lineno, end_col_offset = tok.end

tests/core/test_storage.py

@@ -147,3 +147,131 @@ def test_attr_type_1(enaml_qtbot, enaml_sleep):
     # Should raise a type error
     with pytest.raises(TypeError):
         tester.d = datetime.time(7, 0)
+
+
+#------------------------------------------------------------------------------
+# Const Syntax
+#------------------------------------------------------------------------------
+def test_const_syntax_1():
+    source = dedent("""\
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const editing = False
+    """)
+    compile_source(source, 'Main')
+
+
+def test_const_syntax_2():
+    source = dedent("""\
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const message: str = "Hello world"
+    """)
+    compile_source(source, 'Main')
+
+
+def test_const_syntax_3():
+    # ChildDef const
+    source = dedent("""\
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        Label:
+            const show_extra = False
+    """)
+    compile_source(source, 'Main')
+
+
+def test_bad_const_syntax_1():
+    source = dedent("""\
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const enabled
+    """)
+    with pytest.raises(SyntaxError):
+        compile_source(source, 'Main')
+
+
+def test_bad_const_syntax_2():
+    # Must have an expr
+    source = dedent("""\
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const enabled: bool
+    """)
+    with pytest.raises(SyntaxError):
+        compile_source(source, 'Main')
+
+
+def test_bad_const_syntax_3():
+    # Invalid op
+    source = dedent("""\
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const message: str << str(self)
+    """)
+    with pytest.raises(SyntaxError):
+        compile_source(source, 'Main')
+
+
+def test_const_expr_1(enaml_qtbot, enaml_sleep):
+    import datetime
+    source = dedent("""\
+    import datetime
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const d: datetime.date = datetime.date.today()
+        Container:
+            Label:
+                text << str(d)
+    """)
+    tester = compile_source(source, 'Main')()
+    tester.show()
+    wait_for_window_displayed(enaml_qtbot, tester)
+
+    # const cannot be changed
+    with pytest.raises(TypeError):
+        tester.d = (datetime.datetime.now() - datetime.timedelta(days=1)).date()
+
+
+def test_const_expr_2(enaml_qtbot, enaml_sleep):
+    import datetime
+    source = dedent("""\
+    import datetime
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const d: datetime.date = "1970-1-1"
+    """)
+    tester = compile_source(source, 'Main')()
+    tester.show()
+    wait_for_window_displayed(enaml_qtbot, tester)
+
+    # const type expr invalid
+    with pytest.raises(TypeError):
+        tester.d
+
+
+def test_const_expr_3(enaml_qtbot, enaml_sleep):
+    from datetime import datetime
+    source = dedent("""\
+    import datetime
+    from enaml.widgets.api import *
+
+    enamldef Main(Window):
+        const d: datetime.date = None
+    """)
+    today = datetime.now().date()
+    tester = compile_source(source, 'Main')(d=today)
+    tester.show()
+    wait_for_window_displayed(enaml_qtbot, tester)
+
+    # const initial value can be passed in
+    assert tester.d == today
+