Fix to add some indent in expressions like before

Related-to: micromark/micromark-extension-mdx-expression@103af9a.

lib/index.js

@@ -1,7 +1,8 @@
 /**
  * @import {CompileContext, Extension as FromMarkdownExtension, Handle as FromMarkdownHandle} from 'mdast-util-from-markdown'
- * @import {Handle as ToMarkdownHandle, Options as ToMarkdownExtension} from 'mdast-util-to-markdown'
- * @import {MdxFlowExpression, MdxTextExpression} from '../index.js'
+ * @import {MdxFlowExpression, MdxTextExpression} from 'mdast-util-mdx-expression'
+ * @import {Handle as ToMarkdownHandle, Options as ToMarkdownExtension, State} from 'mdast-util-to-markdown'
+ * @import {Parents} from 'mdast'
  */
 
 import {ok as assert} from 'devlop'
@@ -98,8 +99,22 @@ function exitMdxExpressionData(token) {
 /**
  * @type {ToMarkdownHandle}
  * @param {MdxFlowExpression | MdxTextExpression} node
+ *   Node.
+ * @param {Parents | undefined} parent
+ *   Parent, if any.
+ * @param {State} state
+ *   Info passed around about the current state.
+ * @returns {string}
+ *   Serialized markdown.
  */
-function handleMdxExpression(node) {
+function handleMdxExpression(node, parent, state) {
   const value = node.value || ''
-  return '{' + value + '}'
+  const result = state.indentLines(value, function (line, index, blank) {
+    // Tab-size to eat has to be the same as what we serialize as.
+    // While in some places in markdown that’s 4, in JS it’s more common as 2.
+    // Which is what’s also in `mdast-util-mdx-jsx`:
+    // <https://github.com/syntax-tree/mdast-util-mdx-jsx/blob/40b951b/lib/index.js#L52>
+    return (index === 0 || blank ? '' : '  ') + line
+  })
+  return '{' + result + '}'
 }

test.js

@@ -50,7 +50,7 @@ test('mdxExpressionFromMarkdown()', async function (t) {
   )
 
   await t.test(
-    'should support a flow expression (agnostic)',
+    'should support an indented flow expression (agnostic)',
     async function () {
       assert.deepEqual(
         fromMarkdown('{\n  1 + 1\n}', {
@@ -62,7 +62,7 @@ test('mdxExpressionFromMarkdown()', async function (t) {
           children: [
             {
               type: 'mdxFlowExpression',
-              value: '\n  1 + 1\n',
+              value: '\n1 + 1\n',
               position: {
                 start: {line: 1, column: 1, offset: 0},
                 end: {line: 3, column: 2, offset: 11}
@@ -467,7 +467,7 @@ test('mdxExpressionToMarkdown()', async function (t) {
         },
         {extensions: [mdxExpressionToMarkdown()]}
       ),
-      '{a + b}\n\n{\nc +\n1\n}\n\n{}\n\nd\n'
+      '{a + b}\n\n{\n  c +\n  1\n}\n\n{}\n\nd\n'
     )
   })
 
@@ -516,7 +516,7 @@ test('mdxExpressionToMarkdown()', async function (t) {
 
 test('roundtrip', async function (t) {
   await t.test(
-    'should *not* strip superfluous whitespace depending on the opening prefix, when roundtripping expressions (flow)',
+    'should strip superfluous whitespace depending on the opening prefix, when roundtripping expressions (flow)',
     async function () {
       assert.deepEqual(
         toMarkdown(
@@ -526,7 +526,7 @@ test('roundtrip', async function (t) {
           }),
           {extensions: [mdxExpressionToMarkdown()]}
         ),
-        '{`\n a\n `}\n'
+        '{`\n  a\n  `}\n'
       )
     }
   )