[lldb] Add test for Swift.DecodingError enum

lldb/test/API/lang/swift/enums/decoding_error/Makefile

@@ -0,0 +1,3 @@
+SWIFT_SOURCES := main.swift
+
+include Makefile.rules

lldb/test/API/lang/swift/enums/decoding_error/TestSwiftDecodingErrorEnum.py

@@ -0,0 +1,23 @@
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+import lldbsuite.test.lldbutil as lldbutil
+import os
+
+
+class TestCase(TestBase):
+    @swiftTest
+    @skipUnlessFoundation
+    def test_swift_decoding_error(self):
+        """Regression test for Swift.DecodingError, a specific instance of a multipayload enum."""
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.swift")
+        )
+
+        substrs = [
+            "(DecodingError) ", " = keyNotFound {",
+            'debugDescription = "No value associated with key CodingKeys(stringValue: \\"number\\", intValue: nil)',
+        ]
+        self.expect("frame variable error", substrs=substrs)
+        self.expect("expression error", substrs=substrs)

lldb/test/API/lang/swift/enums/decoding_error/main.swift

@@ -0,0 +1,16 @@
+import Foundation
+
+struct Payload: Decodable {
+    var number: Int
+}
+
+func main() {
+    do {
+        let data = Data(#"{"numero":23}"#.utf8)
+        _ = try JSONDecoder().decode(Payload.self, from: data)
+    } catch {
+        print("break here")
+    }
+}
+
+main()