Fix relation_fields validation to accept primary key indexes (#4376)

* Fix `relation_fields` validation to accept primary key indexes

This resolves prisma/language-tools#1387

---------

Co-authored-by: Jan Piotrowski <piotrowski+github@gmail.com>

psl/psl-core/src/validate/validation_pipeline/validations/relation_fields.rs

@@ -267,23 +267,27 @@ pub(super) fn validate_missing_relation_indexes(relation_field: RelationFieldWal
         // Considers all groups of indexes explicitly declared in the given model.
         // An index group can be:
         // - a singleton (@unique or @id)
-        // - an ordered set (@@unique or @@index)
-        let index_field_groups = model.indexes();
-
-        let referencing_fields_appear_in_index = index_field_groups
-            .map(|index_walker| index_walker.fields().map(|index| index.field_id()))
-            .any(|index_fields_it| {
-                let fields_it = referencing_fields_it.clone();
-                is_leftwise_included_it(fields_it, index_fields_it)
-            });
-
-        if !referencing_fields_appear_in_index {
-            let ast_field = relation_field.ast_field();
-            let span = ast_field
-                .span_for_attribute("relation")
-                .unwrap_or_else(|| ast_field.span());
-            ctx.push_warning(DatamodelWarning::new_missing_index_on_emulated_relation(span));
+        // - an ordered set (@@unique, @@index, or @@id)
+        for index_walker in model.indexes() {
+            let index_fields_it = index_walker.fields().map(|col| col.field_id());
+            let referencing_fields_it = referencing_fields_it.clone();
+            if is_leftwise_included_it(referencing_fields_it, index_fields_it) {
+                return;
+            }
+        }
+
+        if let Some(primary_key_walker) = model.primary_key() {
+            let primary_key_fields_it = primary_key_walker.fields().map(|col| col.field_id());
+            if is_leftwise_included_it(referencing_fields_it, primary_key_fields_it) {
+                return;
+            }
         }
+
+        let ast_field = relation_field.ast_field();
+        let span = ast_field
+            .span_for_attribute("relation")
+            .unwrap_or_else(|| ast_field.span());
+        ctx.push_warning(DatamodelWarning::new_missing_index_on_emulated_relation(span));
     }
 }
 

psl/psl/tests/validation/attributes/index/missing_index_warning/relation_mode_prisma/one_field_at_at_id.prisma

@@ -0,0 +1,19 @@
+// no relation index validation warning on relationMode = "prisma" when a referenced field is already in @@id.
+
+datasource db {
+    provider     = "mysql"
+    url          = env("TEST_DATABASE_URL")
+    relationMode = "prisma"
+}
+
+model SomeUser {
+    id      Int      @id
+    profile Profile?
+}
+
+model Profile {
+    id   Int
+    user SomeUser? @relation(fields: [id], references: [id])
+
+    @@id([id])
+}

psl/psl/tests/validation/attributes/index/missing_index_warning/relation_mode_prisma/one_field_at_id.prisma

@@ -0,0 +1,17 @@
+// no relation index validation warning on relationMode = "prisma" when a referenced field is already in @id.
+
+datasource db {
+    provider     = "mysql"
+    url          = env("TEST_DATABASE_URL")
+    relationMode = "prisma"
+}
+
+model SomeUser {
+    id      Int      @id
+    profile Profile?
+}
+
+model Profile {
+    id   Int       @id
+    user SomeUser? @relation(fields: [id], references: [id])
+}

psl/psl/tests/validation/attributes/index/missing_index_warning/relation_mode_prisma/three_fields_mixed_id.prisma

@@ -0,0 +1,32 @@
+// add missing relation index validation warning on relationMode = "prisma".
+
+datasource db {
+    provider     = "mysql"
+    url          = env("TEST_DATABASE_URL")
+    relationMode = "prisma"
+}
+
+model SomeUser {
+    idA   Int
+    idB   Int
+    idC   Int
+    posts Post[]
+
+    @@id([idA, idB, idC])
+}
+
+model Post {
+    userIdA Int      @unique
+    userIdB Int
+    userIdC Int      @unique
+    user    SomeUser @relation(fields: [userIdA, userIdB, userIdC], references: [idA, idB, idC])
+
+    @@id([userIdA, userIdB])
+}
+
+// warning: With `relationMode = "prisma"`, no foreign keys are used, so relation fields will not benefit from the index usually created by the relational database under the hood. This can lead to poor performance when querying these fields. We recommend adding an index manually. Learn more at https://pris.ly/d/relation-mode-prisma-indexes" 
+//   -->  schema.prisma:22
+//    | 
+// 21 |     userIdC Int      @unique
+// 22 |     user    SomeUser @relation(fields: [userIdA, userIdB, userIdC], references: [idA, idB, idC])
+//    |