[JSON] Added some parse failure test

Author: rintaro

Sources/SwiftCompilerPluginMessageHandling/JSON/JSONDecoding.swift

@@ -29,7 +29,18 @@ import ucrt
 #endif
 
 func decodeFromJSON<T: Decodable>(json: UnsafeBufferPointer<UInt8>) throws -> T {
-  let map = try JSONScanner.scan(buffer: json)
+  let map: JSONMap
+  do {
+    map = try JSONScanner.scan(buffer: json)
+  } catch let err as JSONError {
+    throw DecodingError.dataCorrupted(
+      DecodingError.Context(
+        codingPath: [],
+        debugDescription: "Corrupted JSON",
+        underlyingError: err
+      )
+    )
+  }
   return try map.withValue { value in
     let decoder = JSONDecoding(value: value, codingPathNode: .root)
     return try T.init(from: decoder)
@@ -144,9 +155,19 @@ private struct JSONMapBuilder {
   }
 }
 
-enum JSONError: Error {
+enum JSONError: Error, CustomDebugStringConvertible {
   case unexpectedEndOfFile
   case unexpectedCharacter(UInt8, context: String)
+
+  var debugDescription: String {
+    switch self {
+    case .unexpectedEndOfFile:
+      return "unexpected end of file"
+    case .unexpectedCharacter(let c, let ctxt):
+      let char = c < 0x80 ? String(UnicodeScalar(c)) : "0x" + String(c, radix: 16, uppercase: true)
+      return "unexpected character '\(char)'; \(ctxt)"
+    }
+  }
 }
 
 private struct JSONScanner {
@@ -212,7 +233,7 @@ private struct JSONScanner {
       throw JSONError.unexpectedEndOfFile
     }
     guard ptr.pointee == UInt8(ascii: char) else {
-      throw JSONError.unexpectedCharacter(ptr.pointee, context: "expected \(char)")
+      throw JSONError.unexpectedCharacter(ptr.pointee, context: "expected '\(char)'")
     }
     ptr += 1
   }
@@ -764,7 +785,6 @@ extension JSONDecoding {
     codingPathNode: _CodingPathNode,
     _ additionalKey: (some CodingKey)?
   ) throws -> T {
-    try _checkNotNull(value, expectedType: type, for: codingPathNode, additionalKey)
     let decoder = Self(value: value, codingPathNode: codingPathNode.appending(additionalKey))
     return try T.init(from: decoder)
   }

Tests/SwiftCompilerPluginTest/JSONTests.swift

@@ -15,6 +15,17 @@ import XCTest
 
 final class JSONTests: XCTestCase {
 
+  func testPrimitive() {
+    _testRoundTrip(of: true, expectedJSON: "true")
+    _testRoundTrip(of: false, expectedJSON: "false")
+    _testRoundTrip(of: Bool?.none, expectedJSON: "null")
+    _testRoundTrip(of: "", expectedJSON: "\"\"")
+    _testRoundTrip(of: 0, expectedJSON: "0")
+    _testRoundTrip(of: 0 as Int8, expectedJSON: "0")
+    _testRoundTrip(of: 0.0 as Float, expectedJSON: "0.0")
+    _testRoundTrip(of: 0.0 as Double, expectedJSON: "0.0")
+  }
+
   func testEmptyStruct() {
     let value = EmptyStruct()
     _testRoundTrip(of: value, expectedJSON: "{}")
@@ -73,12 +84,12 @@ final class JSONTests: XCTestCase {
           data: [nil, 42]
         )
       ],
-      elapsed: 42.3
+      elapsed: 42.3e32
     )
     _testRoundTrip(
       of: value,
       expectedJSON: #"""
-        {"diagnostics":[{"animal":"cat","data":[null,42],"message":"error 🛑"}],"elapsed":42.3,"result":"\tresult\nfoo"}
+        {"diagnostics":[{"animal":"cat","data":[null,42],"message":"error 🛑"}],"elapsed":4.23e+33,"result":"\tresult\nfoo"}
         """#
     )
   }
@@ -92,6 +103,33 @@ final class JSONTests: XCTestCase {
     )
   }
 
+  func testParseError() {
+    _assertParseError(
+      #"{"foo": 1"#,
+      message: "unexpected end of file"
+    )
+    _assertParseError(
+      #""foo"#,
+      message: "unexpected end of file"
+    )
+    _assertParseError(
+      "\n",
+      message: "unexpected end of file"
+    )
+    _assertParseError(
+      "trua",
+      message: "unexpected character 'a'; expected 'e'"
+    )
+    _assertParseError(
+      "[true, #foo]",
+      message: "unexpected character '#'; value start"
+    )
+    _assertParseError(
+      "{}true",
+      message: "unexpected character 't'; after top-level value"
+    )
+  }
+
   func testTypeCoercion() {
     _testRoundTripTypeCoercionFailure(of: [false, true], as: [Int].self)
     _testRoundTripTypeCoercionFailure(of: [false, true], as: [Int8].self)
@@ -150,7 +188,25 @@ final class JSONTests: XCTestCase {
       let data = try JSONEncoder().encode(value)
       let _ = try JSONDecoder().decode(U.self, from: data)
       XCTFail("Coercion from \(T.self) to \(U.self) was expected to fail.")
-    } catch {}
+    } catch DecodingError.typeMismatch(_, _) {
+      // Success
+    } catch {
+      XCTFail("unexpected error")
+    }
+  }
+
+  private func _assertParseError(_ json: String, message: String) {
+    do {
+      var json = json
+      _ = try json.withUTF8 { try JSON.decode(Bool.self, from: $0) }
+    } catch DecodingError.dataCorrupted(let context) {
+      XCTAssertEqual(
+        String(describing: try XCTUnwrap(context.underlyingError)),
+        message
+      )
+    } catch {
+      XCTFail("unexpected error")
+    }
   }
 }