Add nicer error on empty expression when forbidden

micromark · Mar 7, 2021 · 6e6d434 · 6e6d434
1 parent 083e0de
commit 6e6d434
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Showing 4 changed files with 29 additions and 20 deletions.
diff --git a/lib/factory-expression.js b/lib/factory-expression.js
@@ -17,7 +17,8 @@ function factoryExpression(
   expressionType,
   expressionMarkerType,
   expressionChunkType,
-  spread
+  spread,
+  forbidEmpty
 ) {
   var self = this
   var eventStart = this.events.length + 3 // Add main and marker token
@@ -105,7 +106,9 @@ function factoryExpression(
     result = eventsToAcorn(acorn, acornOptions, self.events.slice(eventStart), {
       start: startPosition,
       expression: true,
-      allowEmpty: !spread,
+      // To do next major: remove double meaning of `spread` and only accept
+      // `forbidEmpty` here.
+      allowEmpty: !spread && !forbidEmpty,
       prefix: spread ? '({' : '',
       suffix: spread ? '})' : ''
     })
@@ -121,17 +124,7 @@ function factoryExpression(
         estree.body[0].type === 'ExpressionStatement' &&
         estree.body[0].expression.type === 'ObjectExpression'
       ) {
-        if (!estree.body[0].expression.properties[0]) {
-          throw new VMessage(
-            'Unexpected empty spread expression: expected `...`',
-            {
-              line: estree.loc.start.line,
-              column: estree.loc.start.column + 1,
-              offset: estree.start
-            },
-            'micromark-extension-mdx-expression:non-spread'
-          )
-        } else if (estree.body[0].expression.properties[1]) {
+        if (estree.body[0].expression.properties[1]) {
           throw new VMessage(
             'Unexpected extra content in spread: only a single spread is supported',
             {

diff --git a/lib/index.js b/lib/index.js
@@ -11,6 +11,7 @@ function mdxExpression(options) {
   var addResult = settings.addResult
   var acorn = settings.acorn
   var spread
+  var forbidEmpty
   var acornOptions
 
   if (acorn) {
@@ -27,9 +28,11 @@ function mdxExpression(options) {
 
     // Hidden: `micromark-extension-mdx-jsx` supports expressions in tags,
     // and one of them is only “spread” elements.
-    // Instead of duplicating code there is a small hidden feature here to
-    // support that.
+    // It also has expressions that are not allowed to be empty (`<x y={}/>`).
+    // Instead of duplicating code there, this are two small hidden feature here
+    // to test that behavior.
     spread = settings.spread
+    forbidEmpty = settings.forbidEmpty
   } else if (settings.acornOptions || settings.addResult) {
     throw new Error('Expected an `acorn` instance passed in as `options.acorn`')
   }
@@ -59,7 +62,8 @@ function mdxExpression(options) {
         'mdxFlowExpression',
         'mdxFlowExpressionMarker',
         'mdxFlowExpressionChunk',
-        spread
+        spread,
+        forbidEmpty
       )(code)
     }
 
@@ -88,7 +92,8 @@ function mdxExpression(options) {
         'mdxTextExpression',
         'mdxTextExpressionMarker',
         'mdxTextExpressionChunk',
-        spread
+        spread,
+        forbidEmpty
       )(code)
     }
   }

diff --git a/lib/util-events-to-acorn.js b/lib/util-events-to-acorn.js
@@ -1,5 +1,7 @@
 'use strict'
 
+var VMessage = require('vfile-message')
+
 module.exports = eventsToAcorn
 
 // Parse a list of micromark events with acorn.
@@ -51,7 +53,16 @@ function eventsToAcorn(acorn, acornOptions, events, config) {
 
   source = chunks.join('')
   value = before + source + after
-  isEmptyExpression = config.expression && config.allowEmpty && empty(source)
+
+  isEmptyExpression = config.expression && empty(source)
+
+  if (isEmptyExpression && !config.allowEmpty) {
+    throw new VMessage(
+      'Unexpected empty expression',
+      parseOffsetToUnistPoint(0),
+      'micromark-extension-mdx-expression:unexpected-empty-expression'
+    )
+  }
 
   try {
     estree =

diff --git a/test.js b/test.js
@@ -691,7 +691,7 @@ test('micromark-extension-mdx-expression', function (t) {
           extensions: [syntax({acorn: acorn, spread: true})]
         })
       },
-      /Unexpected empty spread expression: expected `\.\.\.`/,
+      /Unexpected empty expression/,
       'should crash on an empty spread'
     )
 
@@ -701,7 +701,7 @@ test('micromark-extension-mdx-expression', function (t) {
           extensions: [syntax({acorn: acorn, spread: true})]
         })
       },
-      /Unexpected empty spread expression: expected `\.\.\.`/,
+      /Unexpected empty expression/,
       'should crash on a comment spread'
     )