Port microsoft#48978 forward to the revised FAR code (microsoft#49267)

* Port microsoft#48978 forward to the revised FAR code

The old regression test didn't catch the corresponding bug in the new code because it hit the fast path where there's only a single project.

* Drop spurious non-null assertion

Author: amcasey

src/server/session.ts

@@ -379,8 +379,8 @@ namespace ts.server {
         // have started the other project searches from related symbols.  Propagate the
         // correct results to all other projects.
 
-        const defaultProjectResults = perProjectResults.get(defaultProject)!;
-        if (defaultProjectResults[0].references[0].isDefinition === undefined) {
+        const defaultProjectResults = perProjectResults.get(defaultProject);
+        if (defaultProjectResults?.[0].references[0]?.isDefinition === undefined) {
             // Clear all isDefinition properties
             perProjectResults.forEach(projectResults => {
                 for (const referencedSymbol of projectResults) {
@@ -580,7 +580,6 @@ namespace ts.server {
 
         return resultsMap;
 
-        // May enqueue to otherPositionQueue
         function searchPosition(project: Project, location: DocumentPosition): readonly TResult[] | undefined {
             const projectResults = getResultsForPosition(project, location);
             if (!projectResults) return undefined;

tests/baselines/reference/referencesInEmptyFileWithMultipleProjects.baseline.jsonc

@@ -0,0 +1,3 @@
+[]
+
+[]

tests/baselines/reference/referencesInStringLiteralValueWithMultipleProjects.baseline.jsonc

@@ -0,0 +1,24 @@
+[
+  {
+    "definition": {
+      "containerKind": "",
+      "containerName": "",
+      "fileName": "/a/a.ts",
+      "kind": "var",
+      "name": "hello",
+      "textSpan": {
+        "start": 56,
+        "length": 5
+      },
+      "displayParts": [
+        {
+          "text": "\"hello\"",
+          "kind": "stringLiteral"
+        }
+      ]
+    },
+    "references": []
+  }
+]
+
+[]

tests/cases/fourslash/server/referencesInEmptyFileWithMultipleProjects.ts

@@ -0,0 +1,16 @@
+/// <reference path="../fourslash.ts"/>
+
+// @Filename: /a/tsconfig.json
+////{ "files": ["a.ts"] }
+
+// @Filename: /a/a.ts
+/////// <reference path="../b/b.ts" />
+/////*1*/;
+
+// @Filename: /b/tsconfig.json
+////{ "files": ["b.ts"] }
+
+// @Filename: /b/b.ts
+/////*2*/;
+
+verify.baselineFindAllReferences('1', '2')

tests/cases/fourslash/server/referencesInStringLiteralValueWithMultipleProjects.ts

@@ -0,0 +1,16 @@
+/// <reference path="../fourslash.ts"/>
+
+// @Filename: /a/tsconfig.json
+////{ "files": ["a.ts"] }
+
+// @Filename: /a/a.ts
+/////// <reference path="../b/b.ts" />
+////const str: string = "hello/*1*/";
+
+// @Filename: /b/tsconfig.json
+////{ "files": ["b.ts"] }
+
+// @Filename: /b/b.ts
+////const str2: string = "hello/*2*/";
+
+verify.baselineFindAllReferences('1', '2')