deprecated-features/rec-set-dynamic-attrs: Downgrade to warning for now

Looks like too much stuff is breaking on this, so let's make it only a
warning for now to ease transition

Change-Id: I52d50ceb1fe1fbe9f4e28d0aabf3537f7e4d52d1

lix/libexpr/parser/state.hh

@@ -234,7 +234,7 @@ inline void State::recSetMergeFound(const AttrPath & attrPath, const PosIdx pos)
 // Added 2025-11-24
 inline void State::recSetDynamicAttrFound(const PosIdx pos)
 {
-    throw ParseError({
+    logWarning({
         .msg = HintFmt(
             "dynamic attributes are not allowed within recursive attrsets, because they would be "
             "evaluated separately from the other recursive attributes. Use %s to disable this "

lix/libutil/deprecated-features/rec-set-dynamic-attrs.md

@@ -4,8 +4,8 @@ internalName: RecSetDynamicAttrs
 timeline:
   - date: 2026-01-30
     release: 2.95.0
-    cls: [4652]
-    message: Introduced as a parser error.
+    cls: [4652, 5067]
+    message: Introduced as a parser warning.
 ---
 Dynamic attrs (attrs with interpolation in the key) are deprecated in `rec` attrsets.
 This is because the recursive dynamics fundamentally do not work with dynamic attributes,

tests/functional2/lang/attrs-dynamic-rec/parse-fail.err.exp

@@ -1,6 +0,0 @@
-error: dynamic attributes are not allowed within recursive attrsets, because they would be evaluated separately from the other recursive attributes. Use --extra-deprecated-features rec-set-dynamic-attrs to disable this error.
-       at /pwd/in.nix:4:5:
-            3|     foo = yep;
-            4|     ${foo} = "awa";
-             |     ^
-            5| }

tests/functional2/lang/attrs-dynamic-rec/parse-okay-warn.err.exp

@@ -0,0 +1,6 @@
+warning: dynamic attributes are not allowed within recursive attrsets, because they would be evaluated separately from the other recursive attributes. Use --extra-deprecated-features rec-set-dynamic-attrs to disable this error.
+         at /pwd/in.nix:4:5:
+              3|     foo = yep;
+              4|     ${foo} = "awa";
+               |     ^
+              5| }

tests/functional2/lang/attrs-dynamic-rec/parse-okay-warn.out.exp

@@ -0,0 +1,18 @@
+_type: ExprSet
+attrs:
+  foo:
+    _type: ExprVar
+    value: yep
+  yep:
+    _type: ExprLiteral
+    value: bar
+    valueType: String
+dynamicAttrs:
+  - name:
+      _type: ExprVar
+      value: foo
+    value:
+      _type: ExprLiteral
+      value: awa
+      valueType: String
+recursive: true

tests/functional2/lang/attrs-dynamic-rec/test.toml

@@ -1,5 +1,6 @@
 [[test]]
-runner = "parse-fail"
+name = "parse-okay-warn"
+runner = "parse-okay"
 matrix = true
 
 [[test]]