Update uri decoder for non encoded comma strings (#52)

### Motivation

Makes decoding of non-percent encoded strings containing commas more
permissive as per discussion in
[278](apple/swift-openapi-generator#278). This
is not strictly necessary to adhere to the Openapi spec, but encompasses
header values that are not percent encoded.

### Modifications

Update the simple unexploded decoder to return a single string of comma
separated values.

### Result

Simple, unexploded nodes containing commas should be decoded correctly.
e.g. `foo, bar` should be a single string, rather than an array.

### Test Plan

Add tests for non percent encoded comma separated strings and percent
encoded strings for additional coverage.

---------

Co-authored-by: bfrearson <>
Co-authored-by: Honza Dvorsky <[email protected]>

Author: bfrearson

Sources/OpenAPIRuntime/URICoder/Decoding/URIValueFromNodeDecoder.swift

@@ -294,6 +294,9 @@ extension URIValueFromNodeDecoder {
             array = try rootValue(in: values)
         }
         guard array.count == 1 else {
+            if style == .simple {
+                return Substring(array.joined(separator: ","))
+            }
             let reason = array.isEmpty ? "an empty node" : "a node with multiple values"
             try throwMismatch("Cannot parse a value from \(reason).")
         }

Tests/OpenAPIRuntimeTests/URICoder/Decoder/Test_URIDecoder.swift

@@ -80,4 +80,30 @@ final class Test_URIDecoder: Test_Runtime {
             XCTAssertEqual(decodedValue, nil)
         }
     }
+
+    func testDecoding_percentEncodedCommaToString() throws {
+        let decoder = URIDecoder(configuration: .simpleUnexplode)
+
+        do {
+            let decodedValue = try decoder.decode(
+                String.self,
+                forKey: "",
+                from: "foo%2C%20bar"
+            )
+            XCTAssertEqual(decodedValue, "foo, bar")
+        }
+    }
+
+    func testDecoding_nonPercentEncodedCommaToString() throws {
+        let decoder = URIDecoder(configuration: .simpleUnexplode)
+
+        do {
+            let decodedValue = try decoder.decode(
+                String.self,
+                forKey: "",
+                from: "foo, bar"
+            )
+            XCTAssertEqual(decodedValue, "foo, bar")
+        }
+    }
 }