feat(yaml): preserve the first document head end marker

src/language-yaml/printer-yaml.js

@@ -169,7 +169,12 @@ function _print(node, parentNode, path, options, print) {
       return join(
         hardline,
         [
-          shouldPrintDocumentHeadEndMarker(node, nextDocument) === "head"
+          shouldPrintDocumentHeadEndMarker(
+            node,
+            nextDocument,
+            parentNode,
+            options
+          ) === "head"
             ? join(
                 hardline,
                 [
@@ -582,8 +587,24 @@ function shouldPrintDocumentEndMarker(document, nextDocument) {
   );
 }
 
-function shouldPrintDocumentHeadEndMarker(document, nextDocument) {
+function shouldPrintDocumentHeadEndMarker(
+  document,
+  nextDocument,
+  root,
+  options
+) {
   if (
+    /**
+     * ---
+     * preserve the first document head end marker
+     */
+    (root.children[0] === document &&
+      /---(\s|$)/.test(
+        options.originalText.slice(
+          options.locStart(document),
+          options.locStart(document) + 4
+        )
+      )) ||
     /**
      * %DIRECTIVE
      * ---

tests/yaml_document/__snapshots__/jsfmt.spec.js.snap

@@ -54,3 +54,28 @@ f
 g
 
 `;
+
+exports[`with-document-head.yml - yaml-verify 1`] = `
+---
+123
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
+123
+
+`;
+
+exports[`with-document-head-like.yml - yaml-verify 1`] = `
+---666
+123
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---666
+123
+
+`;
+
+exports[`without-document-head.yml - yaml-verify 1`] = `
+123
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+123
+
+`;

tests/yaml_document/with-document-head-like.yml

@@ -0,0 +1,2 @@
+---666
+123

tests/yaml_document/with-document-head.yml

@@ -0,0 +1,2 @@
+---
+123

tests/yaml_document/without-document-head.yml

@@ -0,0 +1 @@
+123

tests/yaml_mapping/__snapshots__/jsfmt.spec.js.snap

@@ -302,6 +302,7 @@ exports[`props.yml - yaml-verify 1`] = `
 --- !!map &anchor
 a: 123
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 !!map &anchor
 a: 123
 
@@ -311,6 +312,7 @@ exports[`props.yml - yaml-verify 2`] = `
 --- !!map &anchor
 a: 123
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 !!map &anchor
 a: 123
 

tests/yaml_root/__snapshots__/jsfmt.spec.js.snap

@@ -7,6 +7,7 @@ exports[`documents.yml - yaml-verify 1`] = `
 ---
 456
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 123
 ---
 456
@@ -21,6 +22,7 @@ exports[`documents-with-directive.yml - yaml-verify 1`] = `
 ---
 456
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 123
 ...
 %YAML 1.2
@@ -241,6 +243,7 @@ foobar: !sexy
   - bunny
   - chocolate
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 # Collection Types #############################################################
 ################################################################################
 

tests/yaml_sequence/__snapshots__/jsfmt.spec.js.snap

@@ -113,6 +113,7 @@ exports[`props.yml - yaml-verify 1`] = `
 - 123
 - 456
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 !!set &anchor
 - 123
 - 456
@@ -124,6 +125,7 @@ exports[`props.yml - yaml-verify 2`] = `
 - 123
 - 456
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
 !!set &anchor
 - 123
 - 456