Add integration test reproducing panic when schema is outside project sources

  This test reproduces a panic that occurs when using a multi-project config
  where the schema file is not located within any project's source directory.

  The panic occurs at build_schema.rs:115 with 'no entry found for key' because
  the schema is not loaded into compiler_state.schemas for projects when the
  schema path is outside the project's configured source directory.

  Reproduction: https://github.com/budde377/relay-multirepo-reproduction

Author: captbaritone

compiler/crates/relay-compiler/tests/relay_compiler_integration/fixtures/schema_not_in_project_sources.expected

@@ -0,0 +1,2 @@
+@nocommit
+Run snapshot tests with UPDATE_SNAPSHOTS=1 to update this new file.

compiler/crates/relay-compiler/tests/relay_compiler_integration/fixtures/schema_not_in_project_sources.input

@@ -0,0 +1,36 @@
+//- a/C.js
+graphql`
+  fragment A_data on Query {
+    hello
+  }
+`
+
+//- b/C.js
+graphql`
+  fragment B_data on Query {
+    hello
+  }
+`
+
+//- relay.config.json
+{
+  "projects": {
+    "a": {
+      "schema": "./schema.graphql",
+      "language": "typescript"
+    },
+    "b": {
+      "schema": "./schema.graphql",
+      "language": "typescript"
+    }
+  },
+  "sources": {
+    "a": "a",
+    "b": "b"
+  }
+}
+
+//- schema.graphql
+type Query {
+  hello: String
+}

compiler/crates/relay-compiler/tests/relay_compiler_integration_test.rs

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<58e190b62dc6455639e5995e15b0447b>>
+ * @generated SignedSource<<9b8f55dbad5a1ece9f3780b116bb8730>>
  */
 
 mod relay_compiler_integration;
@@ -446,6 +446,13 @@ async fn resolvers_with_context_path_import() {
     test_fixture(transform_fixture, file!(), "resolvers_with_context_path_import.input", "relay_compiler_integration/fixtures/resolvers_with_context_path_import.expected", input, expected).await;
 }
 
+#[tokio::test]
+async fn schema_not_in_project_sources() {
+    let input = include_str!("relay_compiler_integration/fixtures/schema_not_in_project_sources.input");
+    let expected = include_str!("relay_compiler_integration/fixtures/schema_not_in_project_sources.expected");
+    test_fixture(transform_fixture, file!(), "schema_not_in_project_sources.input", "relay_compiler_integration/fixtures/schema_not_in_project_sources.expected", input, expected).await;
+}
+
 #[tokio::test]
 async fn semantic_null_require_bubble_to_required_parent() {
     let input = include_str!("relay_compiler_integration/fixtures/semantic_null_require_bubble_to_required_parent.input");