[Compile Time Constant Extraction] add variadic args extraction support (#85320)

This PR adds support for extracting variadic arguments to allow
expressions like

```
@parameter(supportedContentTypes: Array(arrayLiteral: .pdf, .text, .jpeg))
var file: IntentFile
```

resolves rdar://163291725

---------

Co-authored-by: Deniz Dizman <ddizman@apple.com>

Author: dendiz

lib/ConstExtract/ConstExtract.cpp

@@ -519,6 +519,11 @@ extractCompileTimeValue(Expr *expr, const DeclContext *declContext) {
       return extractCompileTimeValue(openExistentialExpr->getExistentialValue(), declContext);
     }
 
+    case ExprKind::VarargExpansion: {
+      auto varargExpansionExpr = cast<VarargExpansionExpr>(expr);
+      return extractCompileTimeValue(varargExpansionExpr->getSubExpr(), declContext);
+    }
+
     case ExprKind::ForceValue: {
       auto forceValueExpr = cast<ForceValueExpr>(expr);
       return extractCompileTimeValue(forceValueExpr->getSubExpr(), declContext);

test/ConstExtraction/ExtractVariadicArgs.swift

@@ -0,0 +1,65 @@
+// RUN: %empty-directory(%t)
+// RUN: echo "[MyProto]" > %t/protocols.json
+
+// RUN: %target-swift-frontend -typecheck -emit-const-values-path %t/ExtractVariadicArgs.swiftconstvalues -const-gather-protocols-file %t/protocols.json -primary-file %s
+// RUN: cat %t/ExtractVariadicArgs.swiftconstvalues 2>&1 | %FileCheck %s
+
+protocol MyProto {}
+
+public enum SimpleEnum: MyProto {
+    static func varargs(args: Int...) -> [Int] {
+        args
+    }
+}
+
+public struct Driver: MyProto {
+    static let someInts = SimpleEnum.varargs(args: 1, 2, 3, 4, 5)
+}
+
+// CHECK: "typeName": "ExtractVariadicArgs.Driver",
+// CHECK: "associatedTypeAliases": [],
+// CHECK-NEXT:    "properties": [
+// CHECK-NEXT:      {
+// CHECK-NEXT:        "label": "someInts",
+// CHECK-NEXT:        "type": "Swift.Array<Swift.Int>",
+// CHECK-NEXT:        "mangledTypeName": "n/a - deprecated",
+// CHECK-NEXT:        "isStatic": "true",
+// CHECK-NEXT:        "isComputed": "false",
+// CHECK-NEXT:        "file": "{{.*}}test{{/|\\\\}}ConstExtraction{{/|\\\\}}ExtractVariadicArgs.swift",
+// CHECK-NEXT:        "line": 16,
+// CHECK-NEXT:        "valueKind": "StaticFunctionCall",
+// CHECK-NEXT:        "value": {
+// CHECK-NEXT:          "type": "Swift.Array<Swift.Int>",
+// CHECK-NEXT:          "memberLabel": "varargs",
+// CHECK-NEXT:          "arguments": [
+// CHECK-NEXT:            {
+// CHECK-NEXT:              "label": "args",
+// CHECK-NEXT:              "type": "Swift.Int...",
+// CHECK-NEXT:              "valueKind": "Array",
+// CHECK-NEXT:              "value": [
+// CHECK-NEXT:                {
+// CHECK-NEXT:                  "valueKind": "RawLiteral",
+// CHECK-NEXT:                  "value": "1"
+// CHECK-NEXT:                },
+// CHECK-NEXT:                {
+// CHECK-NEXT:                  "valueKind": "RawLiteral",
+// CHECK-NEXT:                  "value": "2"
+// CHECK-NEXT:                },
+// CHECK-NEXT:                {
+// CHECK-NEXT:                  "valueKind": "RawLiteral",
+// CHECK-NEXT:                  "value": "3"
+// CHECK-NEXT:                },
+// CHECK-NEXT:                {
+// CHECK-NEXT:                  "valueKind": "RawLiteral",
+// CHECK-NEXT:                  "value": "4"
+// CHECK-NEXT:                },
+// CHECK-NEXT:                {
+// CHECK-NEXT:                  "valueKind": "RawLiteral",
+// CHECK-NEXT:                  "value": "5"
+// CHECK-NEXT:                }
+// CHECK-NEXT:              ]
+// CHECK-NEXT:            }
+// CHECK-NEXT:          ]
+// CHECK-NEXT:        }
+// CHECK-NEXT:      }
+// CHECK-NEXT:    ]