fix(markdown): preserve leading/trailing newlines in fenced code block (#5038)

src/language-markdown/embed.js

@@ -6,6 +6,7 @@ const {
   builders: { hardline, literalline, concat, markAsRoot },
   utils: { mapDoc }
 } = require("../doc");
+const { getFencedCodeBlockValue } = require("./utils");
 
 function embed(path, print, textToDoc, options) {
   const node = path.getValue();
@@ -20,7 +21,10 @@ function embed(path, print, textToDoc, options) {
       const style = styleUnit.repeat(
         Math.max(3, util.getMaxContinuousCount(node.value, styleUnit) + 1)
       );
-      const doc = textToDoc(node.value, { parser });
+      const doc = textToDoc(
+        getFencedCodeBlockValue(node, options.originalText),
+        { parser }
+      );
       return markAsRoot(
         concat([
           style,

src/language-markdown/printer-markdown.js

@@ -20,7 +20,7 @@ const {
   utils: { mapDoc },
   printer: { printDocToString }
 } = require("../doc");
-const { getOrderedListItemInfo } = require("./utils");
+const { getOrderedListItemInfo, getFencedCodeBlockValue } = require("./utils");
 
 const TRAILING_HARDLINE_NODES = ["importExport"];
 
@@ -221,7 +221,10 @@ function genericPrint(path, options, print) {
         style,
         node.lang || "",
         hardline,
-        join(hardline, node.value.split("\n")),
+        join(
+          hardline,
+          getFencedCodeBlockValue(node, options.originalText).split("\n")
+        ),
         hardline,
         style
       ]);

src/language-markdown/utils.js

@@ -11,6 +11,43 @@ function getOrderedListItemInfo(orderListItem, originalText) {
   return { numberText, marker, leadingSpaces };
 }
 
+// workaround for https://github.com/remarkjs/remark/issues/351
+// leading and trailing newlines are stripped by remark
+function getFencedCodeBlockValue(node, originalText) {
+  const text = originalText.slice(
+    node.position.start.offset,
+    node.position.end.offset
+  );
+
+  const leadingSpaceCount = text.match(/^\s*/)[0].length;
+  const replaceRegex = new RegExp(`^\\s{0,${leadingSpaceCount}}`);
+
+  const lineContents = text.split("\n");
+
+  const markerStyle = text[leadingSpaceCount]; // ` or ~
+  const marker = text
+    .slice(leadingSpaceCount)
+    .match(new RegExp(`^[${markerStyle}]+`))[0];
+
+  // https://spec.commonmark.org/0.28/#example-104: Closing fences may be indented by 0-3 spaces
+  // https://spec.commonmark.org/0.28/#example-93: The closing code fence must be at least as long as the opening fence
+  const hasEndMarker = new RegExp(`^\\s{0,3}${marker}`).test(
+    lineContents[lineContents.length - 1].slice(
+      getIndent(lineContents.length - 1)
+    )
+  );
+
+  return lineContents
+    .slice(1, hasEndMarker ? -1 : undefined)
+    .map((x, i) => x.slice(getIndent(i + 1)).replace(replaceRegex, ""))
+    .join("\n");
+
+  function getIndent(lineIndex) {
+    return node.position.indent[lineIndex - 1] - 1;
+  }
+}
+
 module.exports = {
+  getFencedCodeBlockValue,
   getOrderedListItemInfo
 };

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

@@ -109,9 +109,11 @@ console.log("hello world!");
 \`\`\`\`\`\`\`\`\`\`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 \`\`\`\`
+
 \`\`\`js
 console.log("hello world!");
 \`\`\`
+
 \`\`\`\`
 
 `;
@@ -195,6 +197,25 @@ console.log("hello world");
 
 `;
 
+exports[`leading-trailing-newlines.md - markdown-verify 1`] = `
+\`\`\`
+
+
+123
+
+
+\`\`\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\`\`\`
+
+
+123
+
+
+\`\`\`
+
+`;
+
 exports[`simple.md - markdown-verify 1`] = `
 \`\`\`
 hello world

tests/markdown_code/leading-trailing-newlines.md

@@ -0,0 +1,7 @@
+```
+
+
+123
+
+
+```

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

@@ -1000,6 +1000,7 @@ exports[`example-94.md - markdown-verify 1`] = `
 aaa
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 \`\`\`\`
+
 \`\`\`
 aaa
 \`\`\`\`
@@ -1028,6 +1029,7 @@ exports[`example-96.md - markdown-verify 1`] = `
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 \`\`\`
 
+
 \`\`\`
 
 `;
@@ -2545,6 +2547,7 @@ bar
 bar
 
 \`\`\`\`
+
 - baz
 
 + \`\`\`