Issue #175 - implement array with indicator indentation flag

Author: dswiecki

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

@@ -116,6 +116,15 @@ public enum Feature implements FormatFeature // since 2.9
          * @since 2.9
          */
         INDENT_ARRAYS(false),
+        /**
+         * Feature enabling of which adds indentation with indicator for array entry generation
+         * (default indentation being 2 spaces).
+         *<p>
+         * Default value is `false` for backwards compatibility
+         *
+         * @since 2.12.0
+         */
+        INDENT_ARRAYS_WITH_INDICATOR(false),
 
         /**
          * Option passed to SnakeYAML that determines if the line breaks used for
@@ -291,6 +300,10 @@ protected DumperOptions buildDumperOptions(int jsonFeatures, int yamlFeatures,
             opt.setIndicatorIndent(1);
             opt.setIndent(2);
         }
+        if (Feature.INDENT_ARRAYS_WITH_INDICATOR.enabledIn(_formatFeatures)) {
+            opt.setIndicatorIndent(2);
+            opt.setIndentWithIndicator(true);
+        }
         // 14-May-2018: [dataformats-text#84] allow use of platform linefeed
         if (Feature.USE_PLATFORM_LINE_BREAKS.enabledIn(_formatFeatures)) {
             opt.setLineBreak(DumperOptions.LineBreak.getPlatformLineBreak());

yaml/src/test/java/com/fasterxml/jackson/dataformat/yaml/ser/GeneratorFeature175Test.java

@@ -0,0 +1,48 @@
+package com.fasterxml.jackson.dataformat.yaml.ser;
+
+import com.fasterxml.jackson.dataformat.yaml.ModuleTestBase;
+import com.fasterxml.jackson.dataformat.yaml.YAMLGenerator;
+import com.fasterxml.jackson.dataformat.yaml.YAMLMapper;
+
+import java.util.Map;
+
+public class GeneratorFeature175Test extends ModuleTestBase {
+    /*
+    /**********************************************************
+    /* Test methods
+    /**********************************************************
+     */
+
+    // [dataformats-text#175]: arrays indentation with indicator
+    public void testArrayWithIndicatorIndentation() throws Exception {
+        String yamlBefore = "---\n" +
+            "tags:\n" +
+            "  - tag:\n" +
+            "      values:\n" +
+            "        - \"first\"\n" +
+            "        - \"second\"\n" +
+            "      name: \"Mathematics\"";
+
+        YAMLMapper defaultArrayMapper = YAMLMapper.builder()
+            .enable(YAMLGenerator.Feature.INDENT_ARRAYS)
+            .build();
+        Map<?, ?> stuff = defaultArrayMapper.readValue(yamlBefore, Map.class);
+        String defaultYaml = defaultArrayMapper.writeValueAsString(stuff);
+
+        //default array indentation set indicator in separate line
+        assertNotSame(yamlBefore, defaultYaml);
+
+        YAMLMapper arrayWithIndicatorMapper = YAMLMapper.builder()
+            .enable(YAMLGenerator.Feature.INDENT_ARRAYS)
+            .enable(YAMLGenerator.Feature.INDENT_ARRAYS_WITH_INDICATOR)
+            .build();
+
+        String arrayWithIndicatorYaml = arrayWithIndicatorMapper.writeValueAsString(stuff);
+        assertEquals(yamlBefore, arrayWithIndicatorYaml.trim());
+
+        // and do it again to ensure it is parseable (no need to be identical)
+        Map<?, ?> stuff2 = arrayWithIndicatorMapper.readValue(arrayWithIndicatorYaml, Map.class);
+        assertNotNull(stuff2);
+        assertEquals(stuff, stuff2);
+    }
+}