language: Change extern type syntax

Use a '$' instead of a '.' to indicate a type provided in application
code.

The reason for the change is to have a consistent "extern" symbol that
isn't widely used elsewhere and isn't ambiguous in expressions.

blueprintcompiler/language/common.py

@@ -20,7 +20,13 @@
 
 from .. import gir
 from ..ast_utils import AstNode, validate, docs
-from ..errors import CompileError, MultipleErrors
+from ..errors import (
+    CompileError,
+    MultipleErrors,
+    UpgradeWarning,
+    CompileWarning,
+    CodeAction,
+)
 from ..completions_utils import *
 from .. import decompiler as decompile
 from ..decompiler import DecompileCtx, decompiler

blueprintcompiler/language/gobject_object.py

@@ -87,7 +87,7 @@ def validate_parent_type(node, ns: str, name: str, err_msg: str):
 def decompile_object(ctx, gir, klass, id=None):
     gir_class = ctx.type_by_cname(klass)
     klass_name = (
-        decompile.full_name(gir_class) if gir_class is not None else "." + klass
+        decompile.full_name(gir_class) if gir_class is not None else "$" + klass
     )
     if id is None:
         ctx.print(f"{klass_name} {{")

blueprintcompiler/language/types.py

@@ -31,33 +31,41 @@ class TypeName(AstNode):
             UseIdent("class_name"),
         ],
         [
-            ".",
+            AnyOf("$", [".", UseLiteral("old_extern", True)]),
             UseIdent("class_name"),
-            UseLiteral("ignore_gir", True),
+            UseLiteral("extern", True),
         ],
         UseIdent("class_name"),
     )
 
+    @validate()
+    def old_extern(self):
+        if self.tokens["old_extern"]:
+            raise UpgradeWarning(
+                "Use the '$' extern syntax introduced in blueprint 0.8.0",
+                actions=[CodeAction("Use '$' syntax", "$" + self.tokens["class_name"])],
+            )
+
     @validate("class_name")
     def type_exists(self):
-        if not self.tokens["ignore_gir"] and self.gir_ns is not None:
+        if not self.tokens["extern"] and self.gir_ns is not None:
             self.root.gir.validate_type(
                 self.tokens["class_name"], self.tokens["namespace"]
             )
 
     @validate("namespace")
     def gir_ns_exists(self):
-        if not self.tokens["ignore_gir"]:
+        if not self.tokens["extern"]:
             self.root.gir.validate_ns(self.tokens["namespace"])
 
     @property
     def gir_ns(self):
-        if not self.tokens["ignore_gir"]:
+        if not self.tokens["extern"]:
             return self.root.gir.namespaces.get(self.tokens["namespace"] or "Gtk")
 
     @property
     def gir_type(self) -> gir.GirType:
-        if self.tokens["class_name"] and not self.tokens["ignore_gir"]:
+        if self.tokens["class_name"] and not self.tokens["extern"]:
             return self.root.gir.get_type(
                 self.tokens["class_name"], self.tokens["namespace"]
             )