enh(cpp): Improve highlighting of unterminated raw strings

PR highlightjs#1897 switched C++ raw strings to use backreferences, however this
breaks souce files where raw strings are truncated. Like comments, it
would be preferable to highlight them.

- Add `on:begin` and `on:end` to allow more granular matching when
  then end match is dynamic and based on a part of the begin match
- This deprecates the `endSameAsBegin` attribute. That attribute was
  a very specific way to solve this problem, but now we have a much
  more general solution in these added callbacks.

Also related: highlightjs#2259.

Author: davidben

docs/reference.rst

@@ -208,6 +208,7 @@ In this case you can't simply specify the same regexp for ``begin`` and
 ``end`` (say, ``"\\$[a-z]\\$"``), but you can use ``begin: "\\$[a-z]\\$"``
 and ``endSameAsBegin: true``.
 
+
 .. _lexemes:
 
 lexemes

src/highlight.js

@@ -4,6 +4,7 @@ https://highlightjs.org/
 */
 
 import deepFreeze from './vendor/deep_freeze';
+import Response from './lib/response';
 import TokenTreeEmitter from './lib/token_tree';
 import * as regex from './lib/regex';
 import * as utils from './lib/utils';
@@ -118,18 +119,6 @@ const HLJS = function(hljs) {
   function _highlight(languageName, code, ignoreIllegals, continuation) {
     var codeToHighlight = code;
 
-    function endOfMode(mode, lexeme) {
-      if (regex.startsWith(mode.endRe, lexeme)) {
-        while (mode.endsParent && mode.parent) {
-          mode = mode.parent;
-        }
-        return mode;
-      }
-      if (mode.endsWithParent) {
-        return endOfMode(mode.parent, lexeme);
-      }
-    }
-
     function keywordData(mode, match) {
       var matchText = language.case_insensitive ? match[0].toLowerCase() : match[0];
       return Object.prototype.hasOwnProperty.call(mode.keywords, matchText) && mode.keywords[matchText];
@@ -206,7 +195,33 @@ const HLJS = function(hljs) {
       if (mode.className) {
         emitter.openNode(mode.className);
       }
-      top = Object.create(mode, { parent: { value: top } });
+      top = Object.create(mode, {parent: {value: top}});
+      return top;
+    }
+
+    function endOfMode(mode, match, matchPlusRemainder) {
+      let matched = regex.startsWith(mode.endRe, matchPlusRemainder);
+
+      if (matched) {
+        if (mode["before:end"]) {
+          let resp = new Response(mode);
+          mode["before:end"](match, resp);
+          if (resp.ignore)
+            matched = false;
+        }
+
+        if (matched) {
+          while (mode.endsParent && mode.parent) {
+            mode = mode.parent;
+          }
+          return mode;
+        }
+      }
+      // even if before:end fires an `ignore` it's still possible
+      // that we might trigger the end node because of a parent mode
+      if (mode.endsWithParent) {
+        return endOfMode(mode.parent, match, matchPlusRemainder);
+      }
     }
 
     function doIgnore(lexeme) {
@@ -226,12 +241,15 @@ const HLJS = function(hljs) {
     function doBeginMatch(match) {
       var lexeme = match[0];
       var new_mode = match.rule;
-
-      if (new_mode.__onBegin) {
-        const res = new_mode.__onBegin(match) || {};
-        if (res.ignoreMatch) {
-          return doIgnore(lexeme);
-        }
+      var mode;
+
+      let resp = new Response(new_mode);
+      // first internal before callbacks, then the public ones
+      let beforeCallbacks = [new_mode.__beforeBegin, new_mode["before:begin"]];
+      for (let cb of beforeCallbacks) {
+        if (!cb) continue;
+        cb(match, resp);
+        if (resp.ignore) return doIgnore(lexeme);
       }
 
       if (new_mode && new_mode.endSameAsBegin) {
@@ -249,14 +267,19 @@ const HLJS = function(hljs) {
           mode_buffer = lexeme;
         }
       }
-      startNewMode(new_mode);
+      mode = startNewMode(new_mode);
+      if (mode["after:begin"]) {
+        let resp = new Response(mode);
+        mode["after:begin"](match, resp);
+      }
       return new_mode.returnBegin ? 0 : lexeme.length;
     }
 
     function doEndMatch(match) {
       var lexeme = match[0];
       var matchPlusRemainder = codeToHighlight.substr(match.index);
-      var end_mode = endOfMode(top, matchPlusRemainder);
+
+      var end_mode = endOfMode(top, match, matchPlusRemainder);
       if (!end_mode) { return NO_MATCH; }
 
       var origin = top;

src/languages/c-like.js

@@ -44,7 +44,12 @@ export default function(hljs) {
         begin: '(u8?|U|L)?\'(' + CHARACTER_ESCAPES + "|.)", end: '\'',
         illegal: '.'
       },
-      { begin: /(?:u8?|U|L)?R"([^()\\ ]{0,16})\((?:.|\n)*?\)\1"/ }
+      {
+        begin: /(?:u8?|U|L)?R"([^()\\ ]{0,16})\(/,
+        end: /\)([^()\\ ]{0,16})"/,
+        'after:begin': (m, resp) => { resp.data.heredoc = m[1]; },
+        'before:end': function(m, resp) { if (resp.data.heredoc !== m[1]) resp.ignoreMatch(); }
+      }
     ]
   };
 

src/lib/mode_compiler.js

@@ -61,6 +61,7 @@ export function compileLanguage(language) {
       // eslint-disable-next-line no-undefined
       const i = match.findIndex((el, i) => i > 0 && el !== undefined);
       const matchData = this.matchIndexes[i];
+      match.splice(0, i); // // trim off the extra matches
 
       return Object.assign(match, matchData);
     }
@@ -158,11 +159,11 @@ export function compileLanguage(language) {
   }
 
   // TODO: We need negative look-behind support to do this properly
-  function skipIfhasPrecedingOrTrailingDot(match) {
+  function skipIfhasPrecedingOrTrailingDot(match, resp) {
     const before = match.input[match.index - 1];
     const after = match.input[match.index + match[0].length];
     if (before === "." || after === ".") {
-      return { ignoreMatch: true };
+      resp.ignoreMatch();
     }
   }
 
@@ -200,8 +201,8 @@ export function compileLanguage(language) {
     if (mode.compiled) return;
     mode.compiled = true;
 
-    // __onBegin is considered private API, internal use only
-    mode.__onBegin = null;
+    // __beforeBegin is considered private API, internal use only
+    mode.__beforeBegin = null;
 
     mode.keywords = mode.keywords || mode.beginKeywords;
     if (mode.keywords) {
@@ -218,7 +219,7 @@ export function compileLanguage(language) {
         // doesn't allow spaces in keywords anyways and we still check for the boundary
         // first
         mode.begin = '\\b(' + mode.beginKeywords.split(' ').join('|') + ')(?=\\b|\\s)';
-        mode.__onBegin = skipIfhasPrecedingOrTrailingDot;
+        mode.__beforeBegin = skipIfhasPrecedingOrTrailingDot;
       }
       if (!mode.begin)
         mode.begin = /\B|\b/;

src/lib/response.js

@@ -0,0 +1,11 @@
+export default class Response {
+  constructor(mode) {
+    if (mode.data === undefined)
+      mode.data = {};
+    this.data = mode.data;
+  }
+
+  ignoreMatch() {
+    this.ignore = true;
+  }
+}

test/markup/cpp/truncated-block-comment.expect.txt

@@ -0,0 +1,3 @@
+<span class="hljs-comment">/*
+Truncated block comment
+</span>

test/markup/cpp/truncated-block-comment.txt

@@ -0,0 +1,2 @@
+/*
+Truncated block comment

test/markup/cpp/truncated-raw-string.expect.txt

@@ -0,0 +1,5 @@
+<span class="hljs-string">R"foo(
+Truncated raw string
+)nope"
+Still not completed.
+</span>

test/markup/cpp/truncated-raw-string.txt

@@ -0,0 +1,4 @@
+R"foo(
+Truncated raw string
+)nope"
+Still not completed.