Update MD049/emphasis-style and MD050/strong-style to not report intraword asterisks/underscores as violations because exchanging either alters meaning (fixes #789).

demo/markdownlint-browser.js

@@ -6050,9 +6050,12 @@ var _require = __webpack_require__(/*! ../helpers */ "../helpers/helpers.js"),
 var _require2 = __webpack_require__(/*! ../helpers/micromark.cjs */ "../helpers/micromark.cjs"),
   filterByTypes = _require2.filterByTypes,
   tokenIfType = _require2.tokenIfType;
+var intrawordRe = /\w/;
 var impl = function impl(params, onError, type, asterisk, underline) {
   var style = arguments.length > 5 && arguments[5] !== undefined ? arguments[5] : "consistent";
-  var emphasisTokens = filterByTypes(params.parsers.micromark.tokens, [type]);
+  var lines = params.lines,
+    parsers = params.parsers;
+  var emphasisTokens = filterByTypes(parsers.micromark.tokens, [type]);
   var _iterator = _createForOfIteratorHelper(emphasisTokens),
     _step;
   try {
@@ -6068,6 +6071,8 @@ var impl = function impl(params, onError, type, asterisk, underline) {
           style = markupStyle;
         }
         if (style !== markupStyle) {
+          var underscoreIntraword = style === "underscore" && (intrawordRe.test(lines[startSequence.startLine - 1][startSequence.startColumn - 2]) || intrawordRe.test(lines[endSequence.endLine - 1][endSequence.endColumn - 1]));
+          if (!underscoreIntraword) {
             for (var _i = 0, _arr = [startSequence, endSequence]; _i < _arr.length; _i++) {
               var sequence = _arr[_i];
               addError(onError, sequence.startLine, "Expected: ".concat(style, "; Actual: ").concat(markupStyle), undefined, [sequence.startColumn, sequence.text.length], {
@@ -6079,6 +6084,7 @@ var impl = function impl(params, onError, type, asterisk, underline) {
           }
         }
       }
+    }
   } catch (err) {
     _iterator.e(err);
   } finally {

lib/md049-md050.js

@@ -5,10 +5,13 @@
 const { addError, emphasisOrStrongStyleFor } = require("../helpers");
 const { filterByTypes, tokenIfType } = require("../helpers/micromark.cjs");
 
+const intrawordRe = /\w/;
+
 const impl =
   (params, onError, type, asterisk, underline, style = "consistent") => {
+    const { lines, parsers } = params;
     const emphasisTokens =
-      filterByTypes(params.parsers.micromark.tokens, [ type ]);
+      filterByTypes(parsers.micromark.tokens, [ type ]);
     for (const token of emphasisTokens) {
       const { children } = token;
       const childType = `${type}Sequence`;
@@ -20,6 +23,15 @@ const impl =
           style = markupStyle;
         }
         if (style !== markupStyle) {
+          const underscoreIntraword = (style === "underscore") && (
+            intrawordRe.test(
+              lines[startSequence.startLine - 1][startSequence.startColumn - 2]
+            ) ||
+            intrawordRe.test(
+              lines[endSequence.endLine - 1][endSequence.endColumn - 1]
+            )
+          );
+          if (!underscoreIntraword) {
             for (const sequence of [ startSequence, endSequence ]) {
               addError(
                 onError,
@@ -37,6 +49,7 @@ const impl =
           }
         }
       }
+    }
   };
 
 module.exports = [

test/emphasis_style_asterisk.md

@@ -4,7 +4,12 @@ This is *fine*
 
 This is _not_ {MD049}
 
+Internal emphasis is preserved:
+apple*banana*cherry, apple*banana*, *banana*cherry
+apple_banana_cherry, apple_banana_, _banana_cherry
+
 <!-- markdownlint-configure-file {
+  "MD037": false,
   "MD049": {
     "style": "asterisk"
   }

test/emphasis_style_underscore.md

@@ -4,7 +4,12 @@ This is _fine_
 
 This is *not* {MD049}
 
+Internal emphasis is preserved:
+apple*banana*cherry, apple*banana*, *banana*cherry
+apple_banana_cherry, apple_banana_, _banana_cherry
+
 <!-- markdownlint-configure-file {
+  "MD037": false,
   "MD049": {
     "style": "underscore"
   }

test/snapshots/markdownlint-test-scenarios.js.md

@@ -10754,7 +10754,12 @@ Generated by [AVA](https://avajs.dev).
       ␊
       This is *not* {MD049}␊
       ␊
+      Internal emphasis is preserved:␊
+      apple*banana*cherry, apple*banana*, *banana*cherry␊
+      apple_banana_cherry, apple_banana_, _banana_cherry␊
+      ␊
       <!-- markdownlint-configure-file {␊
+        "MD037": false,␊
         "MD049": {␊
           "style": "asterisk"␊
         }␊
@@ -10815,7 +10820,12 @@ Generated by [AVA](https://avajs.dev).
       ␊
       This is _not_ {MD049}␊
       ␊
+      Internal emphasis is preserved:␊
+      apple*banana*cherry, apple*banana*, *banana*cherry␊
+      apple_banana_cherry, apple_banana_, _banana_cherry␊
+      ␊
       <!-- markdownlint-configure-file {␊
+        "MD037": false,␊
         "MD049": {␊
           "style": "underscore"␊
         }␊
@@ -44028,6 +44038,10 @@ Generated by [AVA](https://avajs.dev).
       ␊
       This is **not** {MD050}␊
       ␊
+      Internal emphasis is preserved:␊
+      apple**banana**cherry, apple**banana**, **banana**cherry␊
+      apple__banana__cherry, apple__banana__, __banana__cherry␊
+      ␊
       <!-- markdownlint-configure-file {␊
         "MD050": {␊
           "style": "asterisk"␊
@@ -44089,6 +44103,10 @@ Generated by [AVA](https://avajs.dev).
       ␊
       This is __not__ {MD050}␊
       ␊
+      Internal emphasis is preserved:␊
+      apple**banana**cherry, apple**banana**, **banana**cherry␊
+      apple__banana__cherry, apple__banana__, __banana__cherry␊
+      ␊
       <!-- markdownlint-configure-file {␊
         "MD050": {␊
           "style": "underscore"␊

test/strong_style_asterisk.md

@@ -4,6 +4,10 @@ This is **fine**
 
 This is __not__ {MD050}
 
+Internal emphasis is preserved:
+apple**banana**cherry, apple**banana**, **banana**cherry
+apple__banana__cherry, apple__banana__, __banana__cherry
+
 <!-- markdownlint-configure-file {
   "MD050": {
     "style": "asterisk"

test/strong_style_underscore.md

@@ -4,6 +4,10 @@ This is __fine__
 
 This is **not** {MD050}
 
+Internal emphasis is preserved:
+apple**banana**cherry, apple**banana**, **banana**cherry
+apple__banana__cherry, apple__banana__, __banana__cherry
+
 <!-- markdownlint-configure-file {
   "MD050": {
     "style": "underscore"