fix: support where argument on field-level @unique for partial indexes (#5774)

## fix: support `where` argument on field-level `@unique` for partial
indexes

### Summary

- Add `where` clause parsing to field-level `@unique`, fixing "No such
argument" validation error when `db pull` generates `@unique(where:
raw("..."))` for single-column partial unique indexes.

### Changes

- `psl/parser-database/src/attributes.rs`: Call `parse_where_clause()`
in `visit_field_unique`, matching the existing behavior in
`model_unique` / `model_index`.
- `psl/psl/tests/attributes/partial_index.rs`: 4 new tests covering raw
syntax, object syntax, missing preview feature error, and `map` +
`where` combination.

### Test plan

- [x] All existing partial index tests pass (52 total)
- [x] `make test-unit` passes
- [x] Verified with reproduction repo from prisma/prisma#29172. `prisma
generate` succeeds after fix

Closes #5773

Author: jay-l-e-e

psl/parser-database/src/attributes.rs

@@ -271,7 +271,7 @@ fn visit_scalar_field_attributes(
 
     // @unique
     if ctx.visit_optional_single_attr("unique") {
-        visit_field_unique(scalar_field_id, model_data, ctx);
+        visit_field_unique(scalar_field_id, model_id, model_data, ctx);
         ctx.validate_visited_arguments();
     }
 
@@ -284,7 +284,12 @@ fn visit_scalar_field_attributes(
     ctx.validate_visited_attributes();
 }
 
-fn visit_field_unique(scalar_field_id: ScalarFieldId, model_data: &mut ModelAttributes, ctx: &mut Context<'_>) {
+fn visit_field_unique(
+    scalar_field_id: ScalarFieldId,
+    model_id: crate::ModelId,
+    model_data: &mut ModelAttributes,
+    ctx: &mut Context<'_>,
+) {
     let mapped_name = match ctx
         .visit_optional_arg("map")
         .and_then(|arg| coerce::string(arg, ctx.diagnostics))
@@ -318,6 +323,7 @@ fn visit_field_unique(scalar_field_id: ScalarFieldId, model_data: &mut ModelAttr
     };
 
     let clustered = validate_clustering_setting(ctx);
+    let where_clause = parse_where_clause(model_id, ctx);
 
     let attribute_id = ctx.current_attribute_id();
     model_data.ast_indexes.push((
@@ -333,6 +339,7 @@ fn visit_field_unique(scalar_field_id: ScalarFieldId, model_data: &mut ModelAttr
             source_field: Some(scalar_field_id),
             mapped_name,
             clustered,
+            where_clause,
             ..Default::default()
         },
     ))

psl/psl/tests/attributes/partial_index.rs

@@ -1030,3 +1030,76 @@ fn partial_index_object_syntax_rejects_boolean_for_enum_field() {
     "#]];
     expected.assert_eq(&err);
 }
+
+#[test]
+fn field_level_partial_unique_with_raw_on_postgres() {
+    let dml = indoc! {r#"
+        model User {
+            id     Int    @id
+            email  String @unique(where: raw("status = 'active'"))
+            status String
+        }
+    "#};
+
+    psl::parse_schema_without_extensions(with_header(dml, Provider::Postgres, &["partialIndexes"]))
+        .unwrap()
+        .assert_has_model("User")
+        .assert_unique_on_fields(&["email"])
+        .assert_raw_where_clause("status = 'active'");
+}
+
+#[test]
+fn field_level_partial_unique_with_object_syntax() {
+    let dml = indoc! {r#"
+        model User {
+            id     Int     @id
+            email  String  @unique(where: { active: true })
+            active Boolean
+        }
+    "#};
+
+    psl::parse_schema_without_extensions(with_header(dml, Provider::Postgres, &["partialIndexes"]))
+        .unwrap()
+        .assert_has_model("User")
+        .assert_unique_on_fields(&["email"])
+        .assert_where_object(&[("active", WhereCondition::Equals(WhereValue::Boolean(true)))]);
+}
+
+#[test]
+fn field_level_partial_unique_requires_preview_feature() {
+    let dml = indoc! {r#"
+        model User {
+            id     Int    @id
+            email  String @unique(where: raw("status = 'active'"))
+            status String
+        }
+    "#};
+
+    let err = parse_unwrap_err(&with_header(dml, Provider::Postgres, &[]));
+    let expected = expect![[r#"
+        error: Error parsing attribute "@unique": Partial indexes are a preview feature. Add "partialIndexes" to previewFeatures in your generator block.
+          -->  schema.prisma:12
+           | 
+        11 |     id     Int    @id
+        12 |     email  String @unique(where: raw("status = 'active'"))
+           | 
+    "#]];
+    expected.assert_eq(&err);
+}
+
+#[test]
+fn field_level_partial_unique_with_map() {
+    let dml = indoc! {r#"
+        model User {
+            id     Int    @id
+            email  String @unique(map: "email_active_idx", where: raw("status = 'active'"))
+            status String
+        }
+    "#};
+
+    psl::parse_schema_without_extensions(with_header(dml, Provider::Postgres, &["partialIndexes"]))
+        .unwrap()
+        .assert_has_model("User")
+        .assert_unique_on_fields(&["email"])
+        .assert_raw_where_clause("status = 'active'");
+}