Merge branch 'pmderodat/null_resolved_node' into 'master'

Lexical envs: filter out null nodes from resolved entities in lookups

Closes AdaCore#653

See merge request eng/libadalang/langkit!833

Author: pmderodat

langkit/support/langkit_support-lexical_envs_impl.adb

@@ -1035,8 +1035,8 @@ package body Langkit_Support.Lexical_Envs_Impl is
       is
          E : constant Entity :=
            (Node => Node.Node,
-            Info => (Md         => Combine (Node.Md, Md),
-                     Rebindings => Rebindings,
+            Info => (Md           => Combine (Node.Md, Md),
+                     Rebindings   => Rebindings,
                      From_Rebound => From_Rebound));
       begin
 
@@ -1052,6 +1052,14 @@ package body Langkit_Support.Lexical_Envs_Impl is
                then E
                else Node.Resolver.all (E));
          begin
+            --  Silently discard null resolved nodes: we tolerate them as they
+            --  likely come from semantic analysis routines running on invalid
+            --  code.
+
+            if Resolved_Entity.Node = No_Node then
+               return;
+            end if;
+
             Resolved_Entity.Info.From_Rebound := From_Rebound;
             Local_Results.Append
               (Lookup_Result_Item'

testsuite/tests/lexical_envs/null_resolved_node/expected_concrete_syntax.lkt

@@ -0,0 +1,16 @@
+import lexer_example
+
+@with_lexer(foo_lexer)
+grammar foo_grammar {
+    @main_rule main_rule <- Example(@example)
+}
+
+@abstract class FooNode implements Node[FooNode] {
+
+    fun resolver(): FooNode = null
+}
+
+class Example : FooNode implements TokenNode {
+
+    @export fun get_all_foo(): Array[FooNode] = node.children_env().get("foo")
+}

testsuite/tests/lexical_envs/null_resolved_node/main.py

@@ -0,0 +1,17 @@
+import sys
+
+import libfoolang
+
+
+print("main.py: Running...")
+
+ctx = libfoolang.AnalysisContext()
+ctx.discard_errors_in_populate_lexical_env(False)
+u = ctx.get_from_buffer("main.txt", "example")
+if u.diagnostics:
+    for d in u.diagnostics:
+        print(d)
+    sys.exit(1)
+
+print(f"p_get_all_foo = {u.root.p_get_all_foo}")
+print("main.py: Done.")

testsuite/tests/lexical_envs/null_resolved_node/test.out

@@ -0,0 +1,4 @@
+main.py: Running...
+p_get_all_foo = []
+main.py: Done.
+Done

testsuite/tests/lexical_envs/null_resolved_node/test.py

@@ -0,0 +1,43 @@
+"""
+Check that the lexical env lookups do not yield null entity when an entity
+resolver turns a non-null entity into a null one.
+
+Such null nodes used to be included, which showed up as crashes in "can_reach"
+properties (Self was null).
+"""
+
+from langkit.dsl import ASTNode, T
+from langkit.envs import EnvSpec, add_env, add_to_env
+from langkit.expressions import No, Self, langkit_property, new_env_assoc
+
+from utils import build_and_run
+
+
+class FooNode(ASTNode):
+
+    @langkit_property()
+    def resolver():
+        return No(T.FooNode.entity)
+
+
+class Example(FooNode):
+    token_node = True
+
+    env_spec = EnvSpec(
+        add_env(),
+        add_to_env(
+            new_env_assoc(
+                key="foo",
+                value=Self,
+            ),
+            resolver=T.FooNode.resolver,
+        ),
+    )
+
+    @langkit_property(public=True)
+    def get_all_foo():
+        return Self.children_env.get("foo")
+
+
+build_and_run(lkt_file="expected_concrete_syntax.lkt", py_script="main.py")
+print("Done")

testsuite/tests/lexical_envs/null_resolved_node/test.yaml

@@ -0,0 +1 @@
+driver: python