Improve MINIMIZE_QUOTES handling to avoid quoting for some use of # and :

yaml/src/main/java/com/fasterxml/jackson/dataformat/yaml/YAMLGenerator.java

@@ -175,7 +175,7 @@ private Feature(boolean defaultState) {
      * aliases for booleans, and we better quote such values as keys; although Jackson
      * itself has no problems dealing with them, some other tools do have.
      */
-    // 02-Apr-2019, tatu: Some names will look funny if escaped: let's leave out 
+    // 02-Apr-2019, tatu: Some names will look funny if escaped: let's leave out
     //    single letter case (esp so 'y' won't get escaped)
     private final static Set<String> MUST_QUOTE_NAMES = new HashSet<>(Arrays.asList(
 //            "y", "Y", "n", "N",
@@ -217,7 +217,7 @@ private Feature(boolean defaultState) {
     protected DumperOptions _outputOptions;
 
     protected final org.yaml.snakeyaml.DumperOptions.Version _docVersion;
-    
+
     // for field names, leave out quotes
     private final static DumperOptions.ScalarStyle STYLE_UNQUOTED_NAME = DumperOptions.ScalarStyle.PLAIN;
 
@@ -964,7 +964,7 @@ private boolean _nameNeedsQuoting(String name) {
             return true;
         }
         return false;
-    }    
+    }
 
     private boolean _valueNeedsQuoting(String name) {
         switch (name.charAt(0)) { // caller ensures no empty String
@@ -990,19 +990,28 @@ private boolean _valueNeedsQuoting(String name) {
     /**
      * As per YAML <a href="https://yaml.org/spec/1.2/spec.html#id2788859">Plain Style</a>unquoted
      * strings are restricted to a reduced charset and must be quoted in case they contain
-     * one of the following characters.
+     * one of the following characters or character combinations.
      */
     private static boolean _valueHasQuotableChar(String inputStr) {
         for (int i = 0, end = inputStr.length(); i < end; ++i) {
             switch (inputStr.charAt(i)) {
-            case ':':
-            case '#':
             case '[':
             case ']':
             case '{':
             case '}':
             case ',':
                 return true;
+            case '\t':
+            case ' ':
+                if (i < end - 1 && '#' == inputStr.charAt(i + 1)) {
+                    return true;
+                }
+                break;
+            case ':':
+                if (i < end - 1 && (' ' == inputStr.charAt(i + 1) || '\t' == inputStr.charAt(i + 1))) {
+                    return true;
+                }
+                break;
             default:
             }
         }

yaml/src/test/java/com/fasterxml/jackson/dataformat/yaml/ser/GeneratorWithMinimizeTest.java

@@ -94,15 +94,50 @@ public void testMinimizeQuotesWithNulls() throws Exception
     public void testMinimizeQuotesWithStringsContainingSpecialChars() throws Exception {
         Map<String, String> content;
 
+        String yaml = null;
+
+        /* scenarios with plain scalars */
+
         content = Collections.singletonMap("key", "a:b");
-        String yaml = MINIM_MAPPER.writeValueAsString(content).trim();
+        yaml = MINIM_MAPPER.writeValueAsString(content).trim();
         assertEquals("---\n" +
-                "key: \"a:b\"", yaml);
+                "key: a:b", yaml);
 
         content = Collections.singletonMap("key", "a#b");
         yaml = MINIM_MAPPER.writeValueAsString(content).trim();
         assertEquals("---\n" +
-                "key: \"a#b\"", yaml);
+                "key: a#b", yaml);
+
+        content = Collections.singletonMap("key", "a# b");
+        yaml = MINIM_MAPPER.writeValueAsString(content).trim();
+        assertEquals("---\n" +
+                "key: a# b", yaml);
+
+        // plus also some edge cases (wrt "false" etc checking
+        yaml = MINIM_MAPPER.writeValueAsString(Collections.singletonMap("key", "f:off")).trim();
+        assertEquals("---\n" +
+                "key: f:off", yaml);
+
+
+        /* scenarios with single quoted scalars */
+
+        content = Collections.singletonMap("key", "::");
+        yaml = MINIM_MAPPER.writeValueAsString(content).trim();
+        assertEquals("---\n" +
+                "key: '::'", yaml);
+
+        content = Collections.singletonMap("key", "#");
+        yaml = MINIM_MAPPER.writeValueAsString(content).trim();
+        assertEquals("---\n" +
+                "key: '#'", yaml);
+
+        content = Collections.singletonMap("key", "#a");
+        yaml = MINIM_MAPPER.writeValueAsString(content).trim();
+        assertEquals("---\n" +
+                "key: '#a'", yaml);
+
+
+        /* scenarios with double quoted scalars */
 
         content = Collections.singletonMap("key", "a[b");
         yaml = MINIM_MAPPER.writeValueAsString(content).trim();
@@ -128,10 +163,6 @@ public void testMinimizeQuotesWithStringsContainingSpecialChars() throws Excepti
         assertEquals("---\n" +
                 "key: \"a,b\"", yaml);
 
-        // plus also some edge cases (wrt "false" etc checking
-        yaml = MINIM_MAPPER.writeValueAsString(Collections.singletonMap("key", "f:off")).trim();
-        assertEquals("---\n" +
-                "key: \"f:off\"", yaml);
     }
 
     public void testLiteralStringsMultiLine() throws Exception
@@ -182,7 +213,7 @@ public void testNonQuoteNumberStoredAsString() throws Exception
         String yaml = MINIM_MAPPER.writeValueAsString(Collections.singletonMap("key", "20")).trim();
         assertEquals("---\n" +
                 "key: 20", yaml);
-        
+
         yaml = MINIM_MAPPER.writeValueAsString(Collections.singletonMap("key", "2.0")).trim();
         assertEquals("---\n" +
                 "key: 2.0", yaml);
@@ -213,7 +244,7 @@ public void testNumberKey() throws Exception
                 MINIM_MAPPER.writeValueAsString(stringKeyMap).trim());
 
         // And then true Integer keys
-        
+
         final Map<Integer, String> intKeyMap = Collections.singletonMap(
                 Integer.valueOf(42), "answer");