fix(parsing): accept a higher-minor %YAML version

The %YAML version check accepted only 1.1 and 1.2, rejecting anything else,
so `%YAML 1.3` errored. The spec calls for processing a document whose minor
version is higher than the processor's, with a warning, rather than refusing
it: only a different major version is incompatible.

Accept any well-formed `1.minor` version and reject only a different major
(`2.0`) or a malformed version. Three tests that asserted `%YAML 1.3` was an
error are corrected to use `2.0`, the genuinely incompatible case, and a test
covers that 1.3 now parses.

Raises yaml-test-suite parse-level conformance to 305/333 (91.6%) with the
value-level (100%) and should-error rejection rates unchanged. 486 tests pass.

CHANGELOG.md

@@ -84,6 +84,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- A `%YAML` directive with a higher minor version than 1.2 is now accepted rather than rejected. The
+  spec calls for processing a document with a higher minor version, with a warning, so `%YAML 1.3` is
+  read as a YAML 1.x document instead of erroring. The version check now accepts any well-formed
+  `1.minor` version and rejects only a different major version (`2.0`) or a malformed one. Three tests
+  that asserted `%YAML 1.3` was an error were corrected to use `2.0`. Raises yaml-test-suite parse-level
+  conformance to 305/333 (91.6%), with the should-error rate unchanged.
+
 - A plain scalar that is an inline block sequence item value (`: - b`) now stops folding at a later
   block entry that returns to the sequence's own indent, so the dashes form the rest of the sequence
   rather than folding into the first item. A block entry only recorded its inline node's indent as a

Sources/Parsing/Scanner.Directives.swift

@@ -102,7 +102,10 @@ extension PureYAML.Parsing.Scanner {
         state.pendingDirectiveLine = start.line
         switch name {
         case "%YAML":
-            guard parts.indices.contains(1), parts[1] == "1.1" || parts[1] == "1.2" else {
+            // Any version with major 1 is processable: a higher minor than 1.2 (`%YAML 1.3`) is
+            // accepted, since the spec calls for processing it, with a warning, rather than rejecting
+            // it. Only a different major version, or a malformed one, is incompatible.
+            guard parts.indices.contains(1), isProcessableYAMLVersion(parts[1]) else {
                 throw PureYAML.Parsing.ParseError.incompatibleYAMLDirective(line: start.line)
             }
             // `%YAML` takes exactly one parameter, the version; only a comment may follow it.
@@ -126,4 +129,14 @@ extension PureYAML.Parsing.Scanner {
             return
         }
     }
+
+    /// Whether a `%YAML` version is one this processor can attempt: any `major.minor` with major 1,
+    /// so 1.0 through 1.2 and a higher minor like 1.3 are all accepted; a different major (2.0) or a
+    /// non-numeric version is not.
+    func isProcessableYAMLVersion(_ version: String) -> Bool {
+        let components = version.split(separator: ".", omittingEmptySubsequences: false)
+        return components.count == 2
+            && components[0] == "1"
+            && components.allSatisfy { !$0.isEmpty && $0.allSatisfy(\.isNumber) }
+    }
 }

Tests/ParsingErrorTests.swift

@@ -16,7 +16,7 @@ struct ParsingErrorTests {
         expectParseError("name: \"open", .unterminatedQuotedString(line: 1))
         expectParseError("name: 'open", .unterminatedQuotedString(line: 1))
         expectParseError("second: *missing", .undefinedAlias(anchor: "missing", line: 1, column: 9))
-        expectParseError("%YAML 1.3\n---\nvalue: yes", .incompatibleYAMLDirective(line: 1))
+        expectParseError("%YAML 2.0\n---\nvalue: yes", .incompatibleYAMLDirective(line: 1))
         expectParseError("value: !!int nope", .invalidTaggedScalar(
             tag: "tag:yaml.org,2002:int",
             value: "nope",

Tests/ScannerTests.swift

@@ -264,7 +264,7 @@ struct ScannerTests {
         expectScannerError("anchor: &", .expectedAnchorName(line: 1))
         expectScannerError("alias: *", .expectedAliasName(line: 1))
         expectScannerError("tag: !<tag:example.com,2026:thing", .unterminatedTag(line: 1))
-        expectScannerError("%YAML 1.3\n---\nvalue: yes", .incompatibleYAMLDirective(line: 1))
+        expectScannerError("%YAML 2.0\n---\nvalue: yes", .incompatibleYAMLDirective(line: 1))
         // An unrecognized directive before the document is ignored, but one after content (where a
         // directive cannot appear) is still rejected.
         expectScannerError("value: yes\n%FOO bar", .unsupportedDirective(name: "%FOO", line: 2))

Tests/YAMLDirectiveTests.swift

@@ -6,7 +6,7 @@ struct YAMLDirectiveTests {
     @Test("A malformed or repeated %YAML directive is rejected", arguments: [
         "%YAML 1.2 foo\n---\nx\n", // an extra parameter after the version
         "%YAML 1.2\n%YAML 1.2\n---\nx\n", // a second %YAML directive
-        "%YAML 1.3\n---\nx\n", // an unsupported version
+        "%YAML 2.0\n---\nx\n", // an incompatible major version
     ])
     func test_invalidYAMLDirectiveIsRejected(_ yaml: String) throws {
         #expect(throws: PureYAML.Parsing.ParseError.self) {
@@ -14,6 +14,11 @@ struct YAMLDirectiveTests {
         }
     }
 
+    @Test("A higher minor version is accepted, since the spec calls for processing it with a warning")
+    func test_higherMinorVersionAccepted() throws {
+        #expect(try PureYAML.parse("%YAML 1.3\n---\nx\n") == .string("x"))
+    }
+
     @Test("A well-formed %YAML directive, with an optional trailing comment, is accepted")
     func test_validYAMLDirectiveAccepted() throws {
         let expected = PureYAML.Model.Value.string("x")