Mark allowArbitraryExtensions as affectsProgramStructure (#52437)

src/compiler/commandLineParser.ts

@@ -1221,7 +1221,7 @@ const commandOptionsWithoutBuild: CommandLineOption[] = [
     {
         name: "allowArbitraryExtensions",
         type: "boolean",
-        affectsModuleResolution: true,
+        affectsProgramStructure: true,
         category: Diagnostics.Modules,
         description: Diagnostics.Enable_importing_files_with_any_extension_provided_a_declaration_file_is_present,
         defaultValueDescription: false,

src/testRunner/unittests/tscWatch/programUpdates.ts

@@ -273,6 +273,48 @@ describe("unittests:: tsc-watch:: program updates", () => {
         ]
     });
 
+    verifyTscWatch({
+        scenario,
+        subScenario: "Updates diagnostics when '--allowArbitraryExtensions' changes",
+        commandLineArgs: ["-w", "-p", "/tsconfig.json"],
+        sys: () => {
+            const aTs: File = {
+                path: "/a.ts",
+                content: "import {} from './b.css'"
+            };
+            const bCssTs: File = {
+                path: "/b.d.css.ts",
+                content: "declare const style: string;"
+            };
+            const tsconfig: File = {
+                path: "/tsconfig.json",
+                content: JSON.stringify({
+                    compilerOptions: { allowArbitraryExtensions: true },
+                    files: ["/a.ts"],
+                })
+            };
+            return createWatchedSystem([libFile, aTs, bCssTs, tsconfig]);
+        },
+        edits: [
+            {
+                caption: "Disable  allowArbitraryExtensions",
+                edit: sys => sys.modifyFile("/tsconfig.json", JSON.stringify({
+                    compilerOptions: { allowArbitraryExtensions: false },
+                    files: ["/a.ts"],
+                })),
+                timeouts: sys => sys.checkTimeoutQueueLengthAndRun(1)
+            },
+            {
+                caption: "Enable  allowArbitraryExtensions",
+                edit: sys => sys.modifyFile("/tsconfig.json", JSON.stringify({
+                    compilerOptions: { allowArbitraryExtensions: true },
+                    files: ["/a.ts"],
+                })),
+                timeouts: sys => sys.checkTimeoutQueueLengthAndRun(1),
+            }
+        ]
+    });
+
     verifyTscWatch({
         scenario,
         subScenario: "updates diagnostics and emit for decorators",