Print exotic import-attribute keys in escaped form

Escaped identifiers also arrive as Lident, so keys like
\"some-identifier" are stored verbatim and must print escaped again to be
writable source; only special-casing the type_ -> type normalization was
insufficient. Use the printer's identifier classification, and pin the
display with a fixture (registered in the catalog). Import attributes on
relative-path modules never reach spec comparison - the relative flag
deliberately erases the primitive in signatures - so the fixture uses a
package module name.

Signed-Off-By: Cristiano Calcagno <ccrisccris@gmail.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PCtQiaDijUqA2fujQXvKUw

Author: cristianoc

compiler/syntax/src/res_outcome_printer.ml

@@ -513,11 +513,15 @@ let print_external_module_doc (emn : External_ffi_types.external_module_name) =
       let with_fields =
         import_attributes
         |> List.map (fun (k, v) ->
-               (* digestion stores the source key [type_] as [type]; map it
-                  back so the printed record is writable source *)
-               let k = if k = "type" then "type_" else k in
-               Doc.concat
-                 [Doc.text k; Doc.text ": "; print_string_literal_doc v])
+               (* digestion stores the source key [type_] as [type]; other
+                  keys are stored as written, including exotic ones from
+                  escaped idents (\"some-identifier"), which must print
+                  escaped again to be writable source *)
+               let key =
+                 if k = "type" then Doc.text "type_"
+                 else Res_printer.print_ident_like k
+               in
+               Doc.concat [key; Doc.text ": "; print_string_literal_doc v])
       in
       Doc.concat
         [

tests/ERROR_VARIANTS.md

@@ -357,7 +357,7 @@ Wrapper symptoms attached to inclusion failures. Source: [includemod.ml:23](../c
 | Variant | Status | Fixture | Notes |
 |---|---|---|---|
 | `Missing_field` | ✓ | `super_errors_multi/Iface_missing_value` | |
-| `Value_descriptions` | ✓ | `super_errors_multi/Iface_value_descriptions`, `super_errors_multi/Iface_value_arity_mismatch`, `super_errors_multi/Smoke_interface_mismatch`, `super_errors_multi/Cross_external_spec_mismatch`, `super_errors_multi/Cross_external_payload_name`, `module_sig_value_arity_mismatch*.res` | Arity mismatches print a dedicated hint (implementation vs interface argument counts), including through aliases and nested function types. |
+| `Value_descriptions` | ✓ | `super_errors_multi/Iface_value_descriptions`, `super_errors_multi/Iface_value_arity_mismatch`, `super_errors_multi/Smoke_interface_mismatch`, `super_errors_multi/Cross_external_spec_mismatch`, `super_errors_multi/Cross_external_payload_name`, `super_errors_multi/Cross_external_import_attrs`, `module_sig_value_arity_mismatch*.res` | Arity mismatches print a dedicated hint (implementation vs interface argument counts), including through aliases and nested function types. |
 | `Type_declarations` | ✓ | `super_errors_multi/Iface_type_decl_record`, `super_errors_multi/Iface_type_decl_variant`, `RecordInclusion.res`, `type_decl_function_arity_mismatch.res` | |
 | `Extension_constructors` | ✓ | `super_errors_multi/Iface_extension_constructors` | |
 | `Module_types` | ✓ | `super_errors_multi/Iface_module_types` | |

tests/build_tests/super_errors_multi/expected/Cross_external_import_attrs.expected

@@ -0,0 +1,22 @@
+===== Importattrs.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_external_import_attrs/Importattrs.res:1:1-2:30
+
+  1 │ @module({from: "somepkg", with: {type_: "json", \"some-identifier": "nop
+    │ e"}})
+  2 │ external data: int = "default"
+  3 │ 
+
+  The implementation /.../fixtures/Cross_external_import_attrs/Importattrs.res
+  does not match the interface /.../fixtures/Cross_external_import_attrs/importattrs.cmi:
+  Values do not match:
+    @val @module({from: "somepkg", with: {type_: "json", \"some-identifier": "nope"}}) external data: int =
+  "default"
+  is not included in
+    @val @module({from: "somepkg", with: {type_: "json", \"some-identifier": "yep"}}) external data: int =
+  "default"
+  /.../fixtures/Cross_external_import_attrs/Importattrs.resi:1:1-2:30:
+    Expected declaration
+  /.../fixtures/Cross_external_import_attrs/Importattrs.res:1:1-2:30:
+    Actual declaration

tests/build_tests/super_errors_multi/fixtures/Cross_external_import_attrs/Importattrs.res

@@ -0,0 +1,2 @@
+@module({from: "somepkg", with: {type_: "json", \"some-identifier": "nope"}})
+external data: int = "default"

tests/build_tests/super_errors_multi/fixtures/Cross_external_import_attrs/Importattrs.resi

@@ -0,0 +1,2 @@
+@module({from: "somepkg", with: {type_: "json", \"some-identifier": "yep"}})
+external data: int = "default"