[substitutions] Fix sibling references inside dict-valued substitutions (#16273)

esphome/components/substitutions/__init__.py

@@ -297,7 +297,18 @@ def _push_context(
         """Resolve a variable, recursively resolving any dependencies it references."""
         value = unresolved_vars.pop(key, Missing)
         if value is Missing:
-            return Missing
+            # Either already resolved (in resolved_vars) or currently being
+            # resolved (self-reference from inside a dict-valued substitution).
+            # Returning what we have lets sibling references inside a dict
+            # value, e.g. ``${device.manufacturer}`` inside ``device.name``,
+            # see literal sibling values during their own resolution.
+            return resolved_vars.get(key, Missing)
+        if isinstance(value, dict):
+            # Dict-valued substitutions form a namespace; eagerly publish the
+            # original mapping so its members can reference each other while
+            # the dict's own substitution pass is still running. The entry is
+            # replaced with the fully-substituted dict once recursion returns.
+            resolved_vars[key] = value
         try:
             value = substitute(value, [], resolver_context, True)
         except UndefinedError as err:

tests/unit_tests/fixtures/substitutions/18-dict_self_reference.approved.yaml

@@ -0,0 +1,16 @@
+substitutions:
+  device:
+    manufacturer: espressif
+    model: esp32
+    mac_suffix: ffffff
+    name: espressif-esp32-ffffff
+  network:
+    host: example.com
+    port: 8080
+    url: http://example.com:8080/api
+esphome:
+  name: espressif-esp32-ffffff
+test_list:
+  - espressif-esp32-ffffff
+  - http://example.com:8080/api
+  - espressif/esp32

tests/unit_tests/fixtures/substitutions/18-dict_self_reference.input.yaml

@@ -0,0 +1,18 @@
+substitutions:
+  device:
+    manufacturer: "espressif"
+    model: "esp32"
+    mac_suffix: "ffffff"
+    name: ${device.manufacturer}-${device.model}-${device.mac_suffix}
+  network:
+    host: "example.com"
+    port: 8080
+    url: "http://${network.host}:${network.port}/api"
+
+esphome:
+  name: ${device.name}
+
+test_list:
+  - ${device.name}
+  - ${network.url}
+  - "${device.manufacturer}/${device.model}"