[Compile Time Constant Extraction] Extract InjectIntoOptional arguments

Resolves rdar://106059663

Author: artemcm

lib/ConstExtract/ConstExtract.cpp

@@ -138,6 +138,8 @@ extractFunctionArguments(const ArgumentList *args) {
       if (decl->hasDefaultExpr()) {
         argExpr = decl->getTypeCheckedDefaultExpr();
       }
+    } else if (auto optionalInject = dyn_cast<InjectIntoOptionalExpr>(argExpr)) {
+      argExpr = optionalInject->getSubExpr();
     }
     parameters.push_back({label, type, extractCompileTimeValue(argExpr)});
   }

test/ConstExtraction/ExtractInjectOptional.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: echo "[MyProto]" > %t/protocols.json
+
+// RUN: %target-swift-frontend -typecheck -emit-const-values-path %t/ExtractLiterals.swiftconstvalues -const-gather-protocols-file %t/protocols.json -primary-file %s
+// RUN: cat %t/ExtractLiterals.swiftconstvalues 2>&1 | %FileCheck %s
+
+protocol MyProto {}
+struct InjectablePropertyStruct : MyProto {
+    let init1 = Bat(buz: "hello", fuz: 4)
+}
+
+public struct Bat {
+    let buz: String?
+    let fuz: Int
+
+    init(buz: String? = "", fuz: Int = 0) {
+        self.buz = buz
+        self.fuz = fuz
+    }
+}
+
+// CHECK:      "arguments": [
+// CHECK-NEXT: {
+// CHECK-NEXT:   "label": "buz",
+// CHECK-NEXT:   "type": "Swift.Optional<Swift.String>",
+// CHECK-NEXT:   "valueKind": "RawLiteral",
+// CHECK-NEXT:   "value": "hello"
+// CHECK-NEXT: },
+// CHECK-NEXT: {
+// CHECK-NEXT:   "label": "fuz",
+// CHECK-NEXT:   "type": "Swift.Int",
+// CHECK-NEXT:   "valueKind": "RawLiteral",
+// CHECK-NEXT:   "value": "4"
+// CHECK-NEXT: }
+// CHECK-NEXT: ]