Fail on duplicate keys in a mapping

jpsim · May 6, 2024 · ef128c0 · ef128c0
1 parent 9234124
commit ef128c0
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diff --git a/Sources/Yams/Parser.swift b/Sources/Yams/Parser.swift
@@ -355,6 +355,15 @@ private extension Parser {
             pairs.append((key, value))
             event = try parse()
         }
+        let keys = pairs.map { $0.0 }
+        let duplicateKeys =  Dictionary(grouping: keys, by: {$0}).filter { $1.count > 1 }.keys
+        if let duplicatedKey = duplicateKeys.first {
+            throw YamlError.parser(
+                context: YamlError.Context(text: "expected all keys in mapping to be unique",
+                                           mark: Mark(line: 1, column: 1)),
+                problem: "but found multiple instances of: \(duplicateKeys.compactMap { $0.string })", duplicatedKey.mark!,
+                yaml: yaml)
+        }
         let node = Node.mapping(.init(pairs, tag(firstEvent.mappingTag), event.mappingStyle, firstEvent.startMark))
         if let anchor = firstEvent.mappingAnchor {
             anchors[anchor] = node

diff --git a/Tests/YamsTests/YamlErrorTests.swift b/Tests/YamsTests/YamlErrorTests.swift
@@ -149,6 +149,22 @@ class YamlErrorTests: XCTestCase {
             )
         }
     }
+
+    func testDuplicateKeysCannotBeParsed() throws {
+        let yamlString = """
+            key: value
+            key: different_value
+        """
+        XCTAssertThrowsError(try Parser(yaml: yamlString).singleRoot()) { error in
+            XCTAssertTrue(error is YamlError)
+            XCTAssertEqual("\(error)", """
+                1:5: error: parser: expected all keys in mapping to be unique in line 1, column 1
+                but found multiple instances of: ["key"]:
+                    key: value
+                    ^
+                """)
+        }
+    }
 }
 
 extension YamlErrorTests {