From 5c60e00a90e949358094a66066d262cae5c4267c Mon Sep 17 00:00:00 2001
From: David Anson <david@dlaa.me>
Date: Sat, 11 Apr 2020 12:33:28 -0700
Subject: [PATCH] Update MD037/no-space-in-emphasis to avoid crash, handle more
 scenarios.

---
 lib/md037.js                           | 39 +++++++++++++++-----------
 test/escaped-emphasis-markers.md       | 12 ++++----
 test/spaces_inside_emphasis_markers.md | 31 +++++++++++++++++++-
 3 files changed, 58 insertions(+), 24 deletions(-)

diff --git a/lib/md037.js b/lib/md037.js
index c6af84c9..d4112b8c 100644
--- a/lib/md037.js
+++ b/lib/md037.js
@@ -29,34 +29,31 @@ module.exports = {
         let match = null;
         let emphasisIndex = -1;
         let emphasisLength = 0;
+        let effectiveEmphasisLength = 0;
         // Match all emphasis-looking runs in the line...
         while ((match = emphasisRe.exec(line))) {
           const matchIndex = match.index + match[1].length;
           const matchLength = match[0].length - match[1].length;
           if (emphasisIndex === -1) {
             // New run
+            emphasisIndex = matchIndex + matchLength;
             emphasisLength = matchLength;
-            emphasisIndex = matchIndex + emphasisLength;
-          } else {
-            // Already in a run
-            if (matchLength !== emphasisLength) {
-              // Looks like a run within a run, reset to embedded run
-              emphasisLength += matchLength;
-              emphasisIndex = matchIndex + emphasisLength;
-            }
-            // Extract emphasized content
+            effectiveEmphasisLength = matchLength;
+          } else if (matchLength === effectiveEmphasisLength) {
+            // Close current run
             const content = line.substring(emphasisIndex, matchIndex);
             const leftSpace = leftSpaceRe.test(content);
             const rightSpace = rightSpaceRe.test(content);
             if (leftSpace || rightSpace) {
               // Report the violation
               const contextStart = emphasisIndex - emphasisLength;
-              const contextEnd = matchIndex + emphasisLength;
+              const contextEnd = matchIndex + effectiveEmphasisLength;
               const context = line.substring(contextStart, contextEnd);
               const column = contextStart + 1;
               const length = contextEnd - contextStart;
-              const marker = match[2] || match[3];
-              const fixedText = `${marker}${content.trim()}${marker}`;
+              const leftMarker = line.substring(contextStart, emphasisIndex);
+              const rightMarker = match[2] || match[3];
+              const fixedText = `${leftMarker}${content.trim()}${rightMarker}`;
               addErrorContext(
                 onError,
                 lineIndex + 1,
@@ -71,11 +68,19 @@ module.exports = {
                 }
               );
             }
-            // Update the run
-            emphasisLength -= matchLength;
-            if (!emphasisLength) {
-              emphasisIndex = -1;
-            }
+            // Reset
+            emphasisIndex = -1;
+            emphasisLength = 0;
+            effectiveEmphasisLength = 0;
+          } else if (matchLength === 3) {
+            // Swap internal run length (1->2 or 2->1)
+            effectiveEmphasisLength = matchLength - effectiveEmphasisLength;
+          } else if (effectiveEmphasisLength === 3) {
+            // Downgrade internal run (3->1 or 3->2)
+            effectiveEmphasisLength -= matchLength;
+          } else {
+            // Upgrade to internal run (1->3 or 2->3)
+            effectiveEmphasisLength += matchLength;
           }
         }
       }
diff --git a/test/escaped-emphasis-markers.md b/test/escaped-emphasis-markers.md
index 70f1dba2..cbc74eec 100644
--- a/test/escaped-emphasis-markers.md
+++ b/test/escaped-emphasis-markers.md
@@ -18,16 +18,16 @@ Escaped underscores _ should \_ be ignored by MD037.
 
 ## Double-character markers, start
 
-All should be reported because they are valid single-character
-marker emphasis without spaces.
+All *could* be reported because they are valid single-character
+marker emphasis when no spaces are present.
 
-Escaped asterisks \** should ** be ignored by MD037. {MD037}
+Escaped asterisks \** should ** be ignored by MD037.
 
-Escaped asterisks *\* should ** be ignored by MD037. {MD037}
+Escaped asterisks *\* should ** be ignored by MD037.
 
-Escaped underscores \__ should __ be ignored by MD037. {MD037}
+Escaped underscores \__ should __ be ignored by MD037.
 
-Escaped underscores _\_ should __ be ignored by MD037. {MD037}
+Escaped underscores _\_ should __ be ignored by MD037.
 
 ## Double-character markers, end
 
diff --git a/test/spaces_inside_emphasis_markers.md b/test/spaces_inside_emphasis_markers.md
index b2dff3f8..ae3359bf 100644
--- a/test/spaces_inside_emphasis_markers.md
+++ b/test/spaces_inside_emphasis_markers.md
@@ -115,13 +115,42 @@ This is * an ambiguous * scenario {MD037}
   with *space * problems {MD037}
   throughout * the * content {MD037}
 
-Uncommon scenarios from the CommonMark specification:
+Uncommon scenarios from the CommonMark specification (and some variations):
 ***strong emph***
 ***strong** in emph*
 ***emph* in strong**
 **in strong *emph***
 *in emph **strong***
 
+*** strong emph*** {MD037}
+*** strong** in emph* {MD037}
+*** emph* in strong** {MD037}
+** in strong *emph*** {MD037}
+
+***strong emph *** {MD037}
+***strong** in emph * {MD037}
+***emph* in strong ** {MD037}
+**in strong *emph *** {MD037}
+*in emph **strong *** {MD037}
+
+** *strong emph*** {MD037}
+** *strong** in emph* {MD037}
+** *emph* in strong** {MD037}
+**in strong * emph*** (internal spaces are not detected)
+*in emph ** strong*** (internal spaces are not detected)
+
+***strong emph* ** {MD037}
+***strong ** in emph* (internal spaces are not detected)
+***emph * in strong** (internal spaces are not detected)
+**in strong *emph* ** {MD037}
+*in emph **strong* ** {MD037}
+
+Text *emph***strong** text
+Text * emph***strong** text {MD037}
+Text *emph ***strong** text (internal spaces are not detected)
+Text *emph*** strong** text (internal spaces are not detected)
+Text *emph***strong ** text {MD037}
+
 ```markdown
 Violations * are * allowed in code blocks where emphasis does not apply.
 ```