[gfm] Prevent markdown mode from parsing formatting within vanilla links (closes #4079)

addon/mode/overlay.js

@@ -4,8 +4,12 @@
 // Utility function that allows modes to be combined. The mode given
 // as the base argument takes care of most of the normal mode
 // functionality, but a second (typically simple) mode is used, which
-// can override the style of text. Both modes get to parse all of the
-// text, but when both assign a non-null style to a piece of code, the
+// can override the style of text.
+// If state.overlay.freezeBaseState is true,
+// only the overlay mode will parse the text
+// until state.overlay.freezeBaseState is set to false.
+// Otherwise, both modes get to parse all of the text,
+// but when both assign a non-null style to a piece of code, the
 // overlay wins, unless the combine argument was true and not overridden,
 // or state.overlay.combineTokens was true, in which case the styles are
 // combined.
@@ -47,7 +51,7 @@ CodeMirror.overlayMode = function(base, overlay, combine) {
         state.basePos = state.overlayPos = stream.start;
       }
 
-      if (stream.start == state.basePos) {
+      if (stream.start == state.basePos && !state.overlay.freezeBaseState) {
         state.baseCur = base.token(stream, state.base);
         state.basePos = stream.pos;
       }
@@ -56,6 +60,9 @@ CodeMirror.overlayMode = function(base, overlay, combine) {
         state.overlayCur = overlay.token(stream, state.overlay);
         state.overlayPos = stream.pos;
       }
+      if (state.overlay.freezeBaseState) {
+        state.basePos = state.overlayPos;
+      }
       stream.pos = Math.min(state.basePos, state.overlayPos);
 
       // state.overlay.combineTokens always takes precedence over combine,

mode/gfm/gfm.js

@@ -24,18 +24,13 @@ CodeMirror.defineMode("gfm", function(config, modeConfig) {
       return {
         code: false,
         codeBlock: false,
-        ateSpace: false
-      };
-    },
-    copyState: function(s) {
-      return {
-        code: s.code,
-        codeBlock: s.codeBlock,
-        ateSpace: s.ateSpace
+        ateSpace: false,
+        freezeBaseState: false
       };
     },
     token: function(stream, state) {
       state.combineTokens = null;
+      state.freezeBaseState = false;
 
       // Hack to prevent formatting override inside code blocks (block and inline)
       if (state.codeBlock) {
@@ -104,6 +99,8 @@ CodeMirror.defineMode("gfm", function(config, modeConfig) {
         // And then (issue #1160) simplified to make it not crash the Chrome Regexp engine
         // And then limited url schemes to the CommonMark list, so foo:bar isn't matched as a URL
         state.combineTokens = true;
+        // #4079: Freeze base state until after URL to avoid parsing formatting within link
+        state.freezeBaseState = true;
         return "link";
       }
       stream.next();

mode/gfm/test.js

@@ -162,6 +162,15 @@
   MT("vanillaLinkEmphasis",
      "foo [em *][em&link http://www.example.com/index.html][em *] bar");
 
+  MT("vanillaLinkUnderscoreInParam",
+     "foo [link http://www.example.com/?bar_baz] hello");
+
+  MT("vanillaLinkUnderscoreStartsParam",
+     "foo [link http://www.example.com/?_bar] hello");
+
+  MT("vanillaLinkUnderscoreStartsParamNoSlash",
+     "foo [link http://www.example.com?_bar] hello");
+
   MT("notALink",
      "foo asfd:asdf bar");