[Impeller] Compile simulator specific Metal shader variants. (flutter/engine#33670)

engine/src/flutter/impeller/tools/build_metal_library.py

@@ -31,7 +31,7 @@ def Main():
                     help="The source file to compile. Can be specified multiple times.")
   parser.add_argument("--optimize", action="store_true", default=False,
                     help="If available optimizations must be applied to the compiled Metal sources.")
-  parser.add_argument("--platform", required=True, choices=["mac", "ios"],
+  parser.add_argument("--platform", required=True, choices=["mac", "ios", "ios-simulator"],
                     help="Select the platform.")
 
   args = parser.parse_args()
@@ -52,6 +52,11 @@ def Main():
       "-sdk",
       "iphoneos",
     ]
+  elif args.platform == "ios-simulator":
+    command += [
+      "-sdk",
+      "iphonesimulator",
+    ]
 
   command += [
     "metal",

engine/src/flutter/impeller/tools/impeller.gni

@@ -140,7 +140,11 @@ template("metal_library") {
     }
 
     if (is_ios) {
-      args += [ "--platform=ios" ]
+      if (use_ios_simulator) {
+        args += [ "--platform=ios-simulator" ]
+      } else {
+        args += [ "--platform=ios" ]
+      }
     } else if (is_mac) {
       args += [ "--platform=mac" ]
     } else {