Patch LibYAML to add the indent_mapping_sequence emitter option

When indent_mapping_sequence is truthy, block sequences in mapping
context will be indented like so:

foo:
  - bar
  - baz

pkg/src/api.c

@@ -534,6 +534,18 @@ yaml_emitter_set_indent(yaml_emitter_t *emitter, int indent)
     emitter->best_indent = (1 < indent && indent < 10) ? indent : 2;
 }
 
+/*
+ * Set whether or not to indent block sequences in mapping context.
+ */
+
+YAML_DECLARE(void)
+yaml_emitter_set_indent_mapping_sequence(yaml_emitter_t *emitter, int indent_mapping_sequence)
+{
+    assert(emitter);    /* Non-NULL emitter object expected. */
+
+    emitter->indent_mapping_sequence = indent_mapping_sequence;
+}
+
 /*
  * Set the preferred line width.
  */

pkg/src/emitter.c

@@ -869,7 +869,9 @@ yaml_emitter_emit_block_sequence_item(yaml_emitter_t *emitter,
     if (first)
     {
         if (!yaml_emitter_increase_indent(emitter, 0,
-                    (emitter->mapping_context && !emitter->indention)))
+                    (emitter->mapping_context
+                             && !emitter->indent_mapping_sequence
+                             && !emitter->indention)))
             return 0;
     }
 

pkg/src/yaml.h

@@ -1595,6 +1595,8 @@ typedef struct yaml_emitter_s {
     int canonical;
     /** The number of indentation spaces. */
     int best_indent;
+    /** Whether or not to indent block sequences in mapping context. */
+    int indent_mapping_sequence;
     /** The preferred width of the output lines. */
     int best_width;
     /** Allow unescaped non-ASCII characters? */