feat(markdown): preserve math (#5050)

- preserve inlineMath (`$inline$`) and blockMath:

  ```md
  $$
  block
  $$
  ```
- side effect: `$` always needs to be escaped.

package.json

@@ -54,6 +54,7 @@
     "postcss-selector-parser": "2.2.3",
     "postcss-values-parser": "1.5.0",
     "regexp-util": "1.2.2",
+    "remark-math": "1.0.4",
     "remark-parse": "5.0.0",
     "resolve": "1.5.0",
     "semver": "5.4.1",

src/language-markdown/parser-markdown.js

@@ -6,6 +6,7 @@ const pragma = require("./pragma");
 const parseFrontMatter = require("../utils/front-matter");
 const { mapAst } = require("./utils");
 const mdx = require("./mdx");
+const remarkMath = require("remark-math");
 
 /**
  * based on [MDAST](https://github.com/syntax-tree/mdast) with following modifications:
@@ -35,6 +36,7 @@ function createParse({ isMDX }) {
         )
       )
       .use(frontMatter)
+      .use(remarkMath)
       .use(isMDX ? mdx.esSyntax : identity)
       .use(liquid)
       .use(isMDX ? htmlToJsx : identity);

src/language-markdown/printer-markdown.js

@@ -49,7 +49,8 @@ const INLINE_NODE_TYPES = [
   "sentence",
   "whitespace",
   "word",
-  "break"
+  "break",
+  "inlineMath"
 ];
 
 const INLINE_NODE_WRAPPER_TYPES = INLINE_NODE_TYPES.concat([
@@ -99,7 +100,7 @@ function genericPrint(path, options, print) {
       return printChildren(path, options, print);
     case "word":
       return node.value
-        .replace(/[*]/g, "\\*") // escape all `*`
+        .replace(/[*$]/g, "\\$&") // escape all `*` and `$` (math)
         .replace(
           new RegExp(
             [
@@ -399,6 +400,17 @@ function genericPrint(path, options, print) {
     case "importExport":
     case "jsx":
       return node.value; // fallback to the original text if multiparser failed
+    case "math":
+      return concat([
+        "$$",
+        hardline,
+        node.value
+          ? concat([replaceNewlinesWith(node.value, hardline), hardline])
+          : "",
+        "$$"
+      ]);
+    case "inlineMath":
+      return concat(["$", node.value, "$"]);
 
     case "tableRow": // handled in "table"
     case "listItem": // handled in "list"

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

@@ -0,0 +1,186 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`empty-block.md - markdown-verify 1`] = `
+$$
+$$
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+$$
+$$
+
+`;
+
+exports[`remark-math.md - markdown-verify 1`] = `
+<!-- tests from https://github.com/Rokt33r/remark-math/blob/9e13e49/specs/remark-math.spec.js -->
+
+$$
+\\beta+\\gamma
+$$
+
+---
+
+$\\alpha\\$
+
+---
+
+\\$\\alpha\\$
+
+---
+
+\\\\$\\alpha$
+
+---
+
+\`$\`\\alpha$
+
+---
+
+$\\alpha\`$\` foo
+
+---
+
+$\`\\alpha\`$
+
+---
+
+$\\alpha\\$$
+
+---
+
+$$
+\\alpha\\$
+$$
+
+---
+
+tango
+$$
+\\alpha
+$$
+
+---
+
+$$\\\\alpha$$
+
+---
+
+$$\\alpha$$
+$$
+\\alpha\\beta
+$$
+
+---
+
+> $$
+> \\alpha\\beta
+> $$
+
+---
+
+  $$$
+    \\alpha
+  $$$
+
+---
+
+$$  must
+\\alpha
+$$  be ignored
+
+---
+
+$$
+\\alpha
+$$
+\`\`\`
+code fence
+\`\`\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+<!-- tests from https://github.com/Rokt33r/remark-math/blob/9e13e49/specs/remark-math.spec.js -->
+
+$$
+\\beta+\\gamma
+$$
+
+---
+
+\\$\\alpha\\$
+
+---
+
+\\\\$\\alpha\\$
+
+---
+
+\\\\$\\alpha$
+
+---
+
+\`$\`\\alpha\\$
+
+---
+
+\\$\\alpha\`$\` foo
+
+---
+
+$\`\\alpha\`$
+
+---
+
+$\\alpha\\$$
+
+---
+
+$$
+\\alpha\\$
+$$
+
+---
+
+tango
+
+$$
+\\alpha
+$$
+
+---
+
+$\\\\alpha$
+
+---
+
+$\\alpha$
+
+$$
+\\alpha\\beta
+$$
+
+---
+
+> $$
+> \\alpha\\beta
+> $$
+
+---
+
+$$
+  \\alpha
+$$
+
+---
+
+$$
+\\alpha
+$$
+
+---
+
+$$
+\\alpha
+$$
+
+\`\`\`
+code fence
+\`\`\`
+
+`;

tests/markdown_math/empty-block.md

@@ -0,0 +1,2 @@
+$$
+$$

tests/markdown_math/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, ["markdown"]);

tests/markdown_math/remark-math.md

@@ -0,0 +1,84 @@
+<!-- tests from https://github.com/Rokt33r/remark-math/blob/9e13e49/specs/remark-math.spec.js -->
+
+$$
+\beta+\gamma
+$$
+
+---
+
+$\alpha\$
+
+---
+
+\$\alpha\$
+
+---
+
+\\$\alpha$
+
+---
+
+`$`\alpha$
+
+---
+
+$\alpha`$` foo
+
+---
+
+$`\alpha`$
+
+---
+
+$\alpha\$$
+
+---
+
+$$
+\alpha\$
+$$
+
+---
+
+tango
+$$
+\alpha
+$$
+
+---
+
+$$\\alpha$$
+
+---
+
+$$\alpha$$
+$$
+\alpha\beta
+$$
+
+---
+
+> $$
+> \alpha\beta
+> $$
+
+---
+
+  $$$
+    \alpha
+  $$$
+
+---
+
+$$  must
+\alpha
+$$  be ignored
+
+---
+
+$$
+\alpha
+$$
+```
+code fence
+```

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

@@ -3306,7 +3306,7 @@ exports[`example-284.md - markdown-verify 1`] = `
 exports[`example-285.md - markdown-verify 1`] = `
 \\!\\"\\#\\$\\%\\&\\'\\(\\)\\*\\+\\,\\-\\.\\/\\:\\;\\<\\=\\>\\?\\@\\[\\\\\\]\\^\\_\\\`\\{\\|\\}\\~
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-\\!\\"\\#\\$\\%\\&\\'\\(\\)\\*\\+\\,\\-\\.\\/\\:\\;\\<\\=\\>\\?\\@\\[\\\\\\]\\^\\_\\\`\\{\\|\\}\\~
+\\!\\"\\#\\\\$\\%\\&\\'\\(\\)\\*\\+\\,\\-\\.\\/\\:\\;\\<\\=\\>\\?\\@\\[\\\\\\]\\^\\_\\\`\\{\\|\\}\\~
 
 `;
 
@@ -5914,7 +5914,7 @@ foo baz
 exports[`example-614.md - markdown-verify 1`] = `
 hello $.;'there
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-hello $.;'there
+hello \\$.;'there
 
 `;
 

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

@@ -92,7 +92,7 @@ markdown\`
   - \\\`
   - \\\\\\\`
   - \\\\\\\\
-  - \\$
+  - \\\\$
   - \\u1234
 \`;
 

yarn.lock

@@ -4856,6 +4856,12 @@ regjsparser@^0.3.0:
   dependencies:
     jsesc "~0.5.0"
 
+remark-math@1.0.4:
+  version "1.0.4"
+  resolved "https://registry.yarnpkg.com/remark-math/-/remark-math-1.0.4.tgz#ced46473075ff99e4678a154a1a3d0dde403a9f2"
+  dependencies:
+    trim-trailing-lines "^1.1.0"
+
 remark-parse@5.0.0:
   version "5.0.0"
   resolved "https://registry.yarnpkg.com/remark-parse/-/remark-parse-5.0.0.tgz#4c077f9e499044d1d5c13f80d7a98cf7b9285d95"
@@ -5662,6 +5668,10 @@ trim-trailing-lines@^1.0.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/trim-trailing-lines/-/trim-trailing-lines-1.1.0.tgz#7aefbb7808df9d669f6da2e438cac8c46ada7684"
 
+trim-trailing-lines@^1.1.0:
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/trim-trailing-lines/-/trim-trailing-lines-1.1.1.tgz#e0ec0810fd3c3f1730516b45f49083caaf2774d9"
+
 trim@0.0.1:
   version "0.0.1"
   resolved "https://registry.yarnpkg.com/trim/-/trim-0.0.1.tgz#5858547f6b290757ee95cccc666fb50084c460dd"