Reduce errors when a namespace is not found

When the typelib for a namespace is not found, don't emit "namespace not
imported" errors. Just emit the one error on the import statement.

blueprintcompiler/gir.py

@@ -741,6 +741,7 @@ class Repository(GirNode):
 class GirContext:
     def __init__(self):
         self.namespaces = {}
+        self.not_found_namespaces: T.Set[str] = set()
 
     def add_namespace(self, namespace: Namespace):
         other = self.namespaces.get(namespace.name)
@@ -781,7 +782,7 @@ class GirContext:
 
         ns = ns or "Gtk"
 
-        if ns not in self.namespaces:
+        if ns not in self.namespaces and ns not in self.not_found_namespaces:
             raise CompileError(
                 f"Namespace {ns} was not imported",
                 did_you_mean=(ns, self.namespaces.keys()),

blueprintcompiler/language/imports.py

@@ -76,6 +76,14 @@ class Import(AstNode):
         UseNumberText("version").expected("a version number"),
     )
 
+    @property
+    def namespace(self):
+        return self.tokens["namespace"]
+
+    @property
+    def version(self):
+        return self.tokens["version"]
+
     @validate("namespace", "version")
     def namespace_exists(self):
         gir.get_namespace(self.tokens["namespace"], self.tokens["version"])

blueprintcompiler/language/ui.py

@@ -58,6 +58,8 @@ class UI(AstNode):
             try:
                 if i.gir_namespace is not None:
                     gir_ctx.add_namespace(i.gir_namespace)
+                else:
+                    gir_ctx.not_found_namespaces.add(i.namespace)
             except CompileError as e:
                 e.start = i.group.tokens["namespace"].start
                 e.end = i.group.tokens["version"].end