language: Add expression literals

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

blueprintcompiler/completions.py

@@ -177,6 +177,15 @@ def property_completer(lsp, ast_node, match_variables):
                     docs=prop.doc,
                     detail=prop.detail,
                 )
+            elif prop.type.full_name == "Gtk.Expression":
+                yield Completion(
+                    prop_name,
+                    CompletionItemKind.Property,
+                    sort_text=f"0 {prop_name}",
+                    snippet=f"{prop_name}: expr $0;",
+                    docs=prop.doc,
+                    detail=prop.detail,
+                )
             else:
                 yield Completion(
                     prop_name,

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)
 

blueprintcompiler/outputs/xml/__init__.py

@@ -134,6 +134,11 @@ class XmlOutput(OutputFormat):
                 self._emit_expression(value.expression, xml)
                 xml.end_tag()
 
+        elif isinstance(value, ExprValue):
+            xml.start_tag("property", **props)
+            self._emit_expression(value.expression, xml)
+            xml.end_tag()
+
         elif isinstance(value, ObjectValue):
             xml.start_tag("property", **props)
             self._emit_object(value.object, xml)
@@ -218,12 +223,6 @@ class XmlOutput(OutputFormat):
             xml.put_text(
                 "|".join([str(flag.value or flag.name) for flag in value.child.flags])
             )
-        elif isinstance(value.child, Translated):
-            raise CompilerBugError("translated values must be handled in the parent")
-        elif isinstance(value.child, TypeLiteral):
-            xml.put_text(value.child.type_name.glib_type_name)
-        elif isinstance(value.child, ObjectValue):
-            self._emit_object(value.child.object, xml)
         else:
             raise CompilerBugError()
 
@@ -245,6 +244,9 @@ class XmlOutput(OutputFormat):
             raise CompilerBugError()
 
     def _emit_literal_expr(self, expr: LiteralExpr, xml: XmlEmitter):
+        if expr.is_this:
+            return
+
         if expr.is_object:
             xml.start_tag("constant")
         else:

docs/reference/expressions.rst

@@ -42,8 +42,8 @@ Expressions are composed of property lookups and/or closures. Property lookups a
 
 .. _Syntax LookupExpression:
 
-Lookup Expressions
-------------------
+Lookups
+-------
 
 .. rst-class:: grammar-block
 
@@ -56,8 +56,8 @@ The type of a property expression is the type of the property it refers to.
 
 .. _Syntax ClosureExpression:
 
-Closure Expressions
--------------------
+Closures
+--------
 
 .. rst-class:: grammar-block
 
@@ -72,8 +72,8 @@ Blueprint doesn't know the closure's return type, so closure expressions must be
 
 .. _Syntax CastExpression:
 
-Cast Expressions
-----------------
+Casts
+-----
 
 .. rst-class:: grammar-block
 
@@ -81,7 +81,32 @@ Cast Expressions
 
 Cast expressions allow Blueprint to know the type of an expression when it can't otherwise determine it. This is necessary for closures and for properties of application-defined types.
 
+Example
+~~~~~~~
+
 .. code-block:: blueprint
 
    // Cast the result of the closure so blueprint knows it's a string
-   label: bind $my_closure() as <string>
+   label: bind $format_bytes(template.file-size) as <string>
+
+.. _Syntax ExprValue:
+
+Expression Values
+-----------------
+
+.. rst-class:: grammar-block
+
+   ExprValue = 'expr' :ref:`Expression<Syntax Expression>`
+
+Some APIs take *an expression itself*--not its result--as a property value. For example, `Gtk.BoolFilter <https://docs.gtk.org/gtk4/class.BoolFilter.html>`_ has an ``expression`` property of type `Gtk.Expression <https://docs.gtk.org/gtk4/class.Expression.html>`_. This expression is evaluated for every item in a list model to determine whether the item should be filtered.
+
+To define an expression for such a property, use ``expr`` instead of ``bind``. Inside the expression, you can use the ``item`` keyword to refer to the item being evaluated. You must cast the item to the correct type using the ``as`` keyword, and you can only use ``item`` in a property lookup--you may not pass it to a closure.
+
+Example
+~~~~~~~
+
+.. code-block:: blueprint
+
+   BoolFilter {
+     expression: expr item as <$UserAccount>.active;
+   }

docs/reference/objects.rst

@@ -58,7 +58,7 @@ Properties
 
 .. rst-class:: grammar-block
 
-   Property = <name::ref:`IDENT<Syntax IDENT>`> ':' ( :ref:`Binding<Syntax Binding>` | :ref:`ObjectValue<Syntax ObjectValue>` | :ref:`Value<Syntax Value>` ) ';'
+   Property = <name::ref:`IDENT<Syntax IDENT>`> ':' ( :ref:`Binding<Syntax Binding>` | :ref:`ExprValue<Syntax ExprValue>` | :ref:`ObjectValue<Syntax ObjectValue>` | :ref:`Value<Syntax Value>` ) ';'
 
 Properties specify the details of each object, like a label's text, an image's icon name, or the margins on a container.
 

tests/sample_errors/expr_item_not_cast.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+BoolFilter {
+  expression: expr item.visible;
+}

tests/sample_errors/expr_item_not_cast.err

@@ -0,0 +1 @@
+4,20,4,"item" must be cast to its object type

tests/sample_errors/expr_value_assignment.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+Label {
+  label: expr 1;
+}

tests/sample_errors/expr_value_assignment.err

@@ -0,0 +1 @@
+4,10,4,Cannot convert Gtk.Expression to string

tests/sample_errors/expr_value_closure_arg.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+BoolFilter {
+  expression: expr $closure(item as <Entry>) as <bool>;
+}

tests/sample_errors/expr_value_closure_arg.err

@@ -0,0 +1 @@
+4,29,4,"item" can only be used for looking up properties

tests/sample_errors/expr_value_item.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+BoolFilter {
+  expression: expr item as <Label>;
+}

tests/sample_errors/expr_value_item.err

@@ -0,0 +1 @@
+4,20,4,"item" can only be used for looking up properties

tests/samples/bind_expr_prop.blp

@@ -0,0 +1,9 @@
+using Gtk 4.0;
+
+BoolFilter filter1 {
+  expression: expr true;
+}
+
+BoolFilter filter2 {
+  expression: bind filter1.expression;
+}

tests/samples/bind_expr_prop.ui

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkBoolFilter" id="filter1">
+    <property name="expression">
+      <constant type="gboolean">true</constant>
+    </property>
+  </object>
+  <object class="GtkBoolFilter" id="filter2">
+    <property name="expression" bind-source="filter1" bind-property="expression" bind-flags="sync-create"/>
+  </object>
+</interface>

tests/samples/bind_literal.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+Label {
+  label: bind "Hello, world!";
+}

tests/samples/bind_literal.ui

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkLabel">
+    <binding name="label">
+      <constant type="gchararray">Hello, world!</constant>
+    </binding>
+  </object>
+</interface>

tests/samples/expr_value.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+BoolFilter {
+  expression: expr item as <Entry>.visible;
+}

tests/samples/expr_value.ui

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkBoolFilter">
+    <property name="expression">
+      <lookup name="visible" type="GtkEntry"></lookup>
+    </property>
+  </object>
+</interface>

tests/samples/expr_value_closure.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+BoolFilter {
+  expression: expr $closure(item as <Entry>.visible) as <bool>;
+}

tests/samples/expr_value_closure.ui

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkBoolFilter">
+    <property name="expression">
+      <closure function="closure" type="gboolean">
+        <lookup name="visible" type="GtkEntry"></lookup>
+      </closure>
+    </property>
+  </object>
+</interface>

tests/samples/expr_value_literal.blp

@@ -0,0 +1,5 @@
+using Gtk 4.0;
+
+BoolFilter {
+  expression: expr true;
+}

tests/samples/expr_value_literal.ui

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkBoolFilter">
+    <property name="expression">
+      <constant type="gboolean">true</constant>
+    </property>
+  </object>
+</interface>

tests/test_samples.py

@@ -198,6 +198,7 @@ class TestSamples(unittest.TestCase):
                 "adw_breakpoint_template",
                 "expr_closure",
                 "expr_closure_args",
+                "expr_value_closure",
                 "parseable",
                 "signal",
                 "signal_not_swapped",