language: Add expression literals

Add expression literals, so you can set properties of type
Gtk.Expression.

blueprintcompiler/language/__init__.py

@@ -41,6 +41,7 @@ from .types import ClassName
 from .ui import UI
 from .values import (
     ArrayValue,
+    ExprValue,
     Flag,
     Flags,
     IdentLiteral,

blueprintcompiler/language/contexts.py

@@ -79,3 +79,9 @@ class ScopeCtx:
         for child in node.children:
             if child.context[ScopeCtx] is self:
                 yield from self._iter_recursive(child)
+
+
+@dataclass
+class ExprValueCtx:
+    """Indicates that the context is an expression literal, where the
+    "item" keyword may be used."""

blueprintcompiler/language/expression.py

@@ -81,6 +81,16 @@ class LiteralExpr(ExprBase):
             or self.root.is_legacy_template(self.literal.value.ident)
         )
 
+    @property
+    def is_this(self) -> bool:
+        from .values import IdentLiteral
+
+        return (
+            not self.is_object
+            and isinstance(self.literal.value, IdentLiteral)
+            and self.literal.value.ident == "item"
+        )
+
     @property
     def literal(self):
         from .values import Literal
@@ -91,6 +101,15 @@ class LiteralExpr(ExprBase):
     def type(self) -> T.Optional[GirType]:
         return self.literal.value.type
 
+    @validate()
+    def item_validations(self):
+        if self.is_this:
+            if not isinstance(self.rhs, CastExpr):
+                raise CompileError('"item" must be cast to its object type')
+
+            if not isinstance(self.rhs.rhs, LookupOp):
+                raise CompileError('"item" can only be used for looking up properties')
+
 
 class LookupOp(InfixExpr):
     grammar = [".", UseIdent("property")]
@@ -285,6 +304,9 @@ expr.children = [
 def decompile_lookup(
     ctx: DecompileCtx, gir: gir.GirContext, cdata: str, name: str, type: str
 ):
+    if ctx.parent_node is not None and ctx.parent_node.tag == "property":
+        ctx.print("expr ")
+
     if t := ctx.type_by_cname(type):
         type = decompile.full_name(t)
     else:
@@ -304,6 +326,8 @@ def decompile_lookup(
     if constant is not None:
         if constant == ctx.template_class:
             ctx.print("template." + name)
+        elif constant == "":
+            ctx.print("item as <" + type + ">." + name)
         else:
             ctx.print(constant + "." + name)
         return
@@ -318,6 +342,9 @@ def decompile_lookup(
 def decompile_constant(
     ctx: DecompileCtx, gir: gir.GirContext, cdata: str, type: T.Optional[str] = None
 ):
+    if ctx.parent_node is not None and ctx.parent_node.tag == "property":
+        ctx.print("expr ")
+
     if type is None:
         if cdata == ctx.template_class:
             ctx.print("template")
@@ -330,6 +357,9 @@ def decompile_constant(
 
 @decompiler("closure", skip_children=True)
 def decompile_closure(ctx: DecompileCtx, gir: gir.GirContext, function: str, type: str):
+    if ctx.parent_node is not None and ctx.parent_node.tag == "property":
+        ctx.print("expr ")
+
     if t := ctx.type_by_cname(type):
         type = decompile.full_name(t)
     else:

blueprintcompiler/language/gobject_object.py

@@ -28,7 +28,18 @@ from .common import *
 from .response_id import ExtResponse
 from .types import ClassName, ConcreteClassName
 
-RESERVED_IDS = {"this", "self", "template", "true", "false", "null", "none"}
+RESERVED_IDS = {
+    "this",
+    "self",
+    "template",
+    "true",
+    "false",
+    "null",
+    "none",
+    "item",
+    "expr",
+    "typeof",
+}
 
 
 class ObjectContent(AstNode):

blueprintcompiler/language/gobject_property.py

@@ -21,13 +21,12 @@
 from .binding import Binding
 from .common import *
 from .contexts import ValueTypeCtx
-from .gtkbuilder_template import Template
-from .values import ArrayValue, ObjectValue, Value
+from .values import ArrayValue, ExprValue, ObjectValue, Value
 
 
 class Property(AstNode):
     grammar = Statement(
-        UseIdent("name"), ":", AnyOf(Binding, ObjectValue, Value, ArrayValue)
+        UseIdent("name"), ":", AnyOf(Binding, ExprValue, ObjectValue, Value, ArrayValue)
     )
 
     @property
@@ -35,7 +34,7 @@ class Property(AstNode):
         return self.tokens["name"]
 
     @property
-    def value(self) -> T.Union[Binding, ObjectValue, Value, ArrayValue]:
+    def value(self) -> T.Union[Binding, ExprValue, ObjectValue, Value, ArrayValue]:
         return self.children[0]
 
     @property

blueprintcompiler/language/values.py

@@ -23,7 +23,8 @@ from blueprintcompiler.gir import ArrayType
 from blueprintcompiler.lsp_utils import SemanticToken
 
 from .common import *
-from .contexts import ScopeCtx, ValueTypeCtx
+from .contexts import ExprValueCtx, ScopeCtx, ValueTypeCtx
+from .expression import Expression
 from .gobject_object import Object
 from .types import TypeName
 
@@ -319,7 +320,12 @@ class IdentLiteral(AstNode):
                 if self.ident == "null":
                     if not self.context[ValueTypeCtx].allow_null:
                         raise CompileError("null is not permitted here")
-                else:
+                elif self.ident == "item":
+                    if not self.context[ExprValueCtx]:
+                        raise CompileError(
+                            '"item" can only be used in an expression literal'
+                        )
+                elif self.ident not in ["true", "false"]:
                     raise CompileError(
                         f"Could not find object with ID {self.ident}",
                         did_you_mean=(
@@ -407,6 +413,35 @@ class ObjectValue(AstNode):
             )
 
 
+class ExprValue(AstNode):
+    grammar = [Keyword("expr"), Expression]
+
+    @property
+    def expression(self) -> Expression:
+        return self.children[Expression][0]
+
+    @validate("expr")
+    def validate_for_type(self) -> None:
+        expected_type = self.parent.context[ValueTypeCtx].value_type
+        expr_type = self.root.gir.get_type("Expression", "Gtk")
+        if expected_type is not None and not expected_type.assignable_to(expr_type):
+            raise CompileError(
+                f"Cannot convert Gtk.Expression to {expected_type.full_name}"
+            )
+
+    @docs("expr")
+    def ref_docs(self):
+        return get_docs_section("Syntax ExprValue")
+
+    @context(ExprValueCtx)
+    def expr_literal(self):
+        return ExprValueCtx()
+
+    @context(ValueTypeCtx)
+    def value_type(self):
+        return ValueTypeCtx(None, must_infer_type=True)
+
+
 class Value(AstNode):
     grammar = AnyOf(Translated, Flags, Literal)