Fix alias emitted in mapping

The idea is to make sure that a YAML alias in a mapping is followed by
a space before the :

An issue appeared with the refactoring made recently that made sure
to respect the YAML specification that allows having a `:` in an anchor
and alias name.

Author: ccoVeille

decode_test.go

@@ -606,6 +606,25 @@ var unmarshalTests = []struct {
 		&struct{ B []int }{[]int{1, 2}},
 	},
 
+	// Bug https://github.com/yaml/go-yaml/issues/109
+	{
+		// alias must be followed by a space in mapping node
+		"foo: &bar bar\n*bar : quz\n",
+		map[string]any{"foo": "bar", "bar": "quz"},
+	},
+
+	{
+		// alias can contain various characters specified by the YAML specification
+		"foo: &b./a:r bar\n*b./a:r : quz\n",
+		map[string]any{"foo": "bar", "bar": "quz"},
+	},
+
+	{
+		// alias containing a trailing colon is supported, but can be ambiguous
+		"foo: &bar: bar\n*bar: : quz\n",
+		map[string]any{"foo": "bar", "bar": "quz"},
+	},
+
 	// Bug #1133337
 	{
 		"foo: ''",
@@ -1111,6 +1130,9 @@ var unmarshalErrorTests = []struct {
 	{"a: 1\nb: 2\nc 2\nd: 3\n", "^yaml: line 3: could not find expected ':'$"},
 	{"#\n-\n{", "yaml: line 3: could not find expected ':'"},   // Issue #665
 	{"0: [:!00 \xef", "yaml: incomplete UTF-8 octet sequence"}, // Issue #666
+	// anchor must be followed by a space in mapping node
+	// https://github.com/yaml/go-yaml/issues/109
+	{"foo: bar\n*bar: quz\n", "^yaml: line 2: could not find expected ':'$"},
 	{
 		"a: &a [00,00,00,00,00,00,00,00,00]\n" +
 			"b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]\n" +

emitterc.go

@@ -813,7 +813,16 @@ func (emitter *yamlEmitter) emitBlockMappingKey(event *yamlEvent, first bool) bo
 	}
 	if emitter.checkSimpleKey() {
 		emitter.states = append(emitter.states, yaml_EMIT_BLOCK_MAPPING_SIMPLE_VALUE_STATE)
-		return emitter.emitNode(event, false, false, true, true)
+		if !emitter.emitNode(event, false, false, true, true) {
+			return false
+		}
+
+		if event.typ == yaml_ALIAS_EVENT {
+			// make sure there's a space after the alias
+			return emitter.put(' ')
+		}
+
+		return true
 	}
 	if !emitter.writeIndicator([]byte{'?'}, true, false, true) {
 		return false

node_test.go

@@ -1128,6 +1128,50 @@ var nodeTests = []struct {
 				},
 			}},
 		},
+	}, {
+		"a: &x: 1\n*x: : c\n",
+		yaml.Node{
+			Kind:   yaml.DocumentNode,
+			Line:   1,
+			Column: 1,
+			Content: []*yaml.Node{{
+				Kind:   yaml.MappingNode,
+				Line:   1,
+				Column: 1,
+				Tag:    "!!map",
+				Content: []*yaml.Node{
+					{
+						Kind:   yaml.ScalarNode,
+						Value:  "a",
+						Tag:    "!!str",
+						Line:   1,
+						Column: 1,
+					},
+					saveNode("x:", &yaml.Node{
+						Kind:   yaml.ScalarNode,
+						Value:  "1",
+						Tag:    "!!int",
+						Anchor: "x:",
+						Line:   1,
+						Column: 4,
+					}),
+					{
+						Kind:   yaml.AliasNode,
+						Value:  "x:",
+						Alias:  dropNode("x:"),
+						Line:   2,
+						Column: 1,
+					},
+					{
+						Kind:   yaml.ScalarNode,
+						Value:  "c",
+						Tag:    "!!str",
+						Line:   2,
+						Column: 7,
+					},
+				},
+			}},
+		},
 	}, {
 		"a: &anchor(.!@#$%^&*+=?:;)name [1, 2]\nb: *anchor(.!@#$%^&*+=?:;)name\n",
 		yaml.Node{