copy-tex contrib module (#813)

* copy-tex contrib module

* Factor out replacement code

* Fix lint

* Support for more browsers, in particular Firefox

* Use for loop instead of Array.forEach
* Use replaceChild if replaceWith is unavailable
* Browserify to remove let etc.

* Fix HTML handling, in particular for Edge

* Convert DocumentFragment to HTML directly (via children' outerHTML)
* Set HTML content *before* text content; Edge takes the last only

* Handle .katex-html and .katex-mathml separately

* Implement option 2: CSS user-select: all

Also fix auto-render.js build location

* Revise documentation according to @kevinbarabash's comments

* Split copy-tex.js into it + katex2tex.js

This supports re-use of code in a custom copy handler.

* Document custom copy handler

* Add missing file

contrib/auto-render/Makefile

@@ -2,8 +2,8 @@
 
 build: $(BUILDDIR)/contrib/auto-render.min.js
 
-$(BUILDDIR)/contrib/auto-render.min.js: $(BUILDDIR)/auto-render.js
+$(BUILDDIR)/contrib/auto-render.min.js: $(BUILDDIR)/contrib/auto-render.js
 	$(UGLIFYJS) < $< > $@
 
-$(BUILDDIR)/auto-render.js: auto-render.js
+$(BUILDDIR)/contrib/auto-render.js: auto-render.js
 	$(BROWSERIFY) -t [ babelify ] $< --standalone renderMathInElement > $@

contrib/copy-tex/Makefile

@@ -0,0 +1,15 @@
+.PHONY: build
+
+build: $(BUILDDIR)/contrib/copy-tex.min.js $(BUILDDIR)/contrib/copy-tex.css $(BUILDDIR)/contrib/copy-tex.min.css
+
+$(BUILDDIR)/contrib/copy-tex.min.js: $(BUILDDIR)/contrib/copy-tex.js
+	$(UGLIFYJS) < $< > $@
+
+$(BUILDDIR)/contrib/copy-tex.js: copy-tex.js
+	$(BROWSERIFY) -t [ babelify ] $< --standalone renderMathInElement > $@
+
+$(BUILDDIR)/contrib/copy-tex.css: copy-tex.css
+	cp $< $@
+
+$(BUILDDIR)/contrib/copy-tex.min.css: $(BUILDDIR)/contrib/copy-tex.css
+	$(CLEANCSS) -o $@ $<

contrib/copy-tex/README.md

@@ -0,0 +1,49 @@
+# Copy-tex extension
+
+This extension modifes the copy/paste behavior in any browser supporting the
+[Clipboard API](https://developer.mozilla.org/en-US/docs/Web/API/ClipboardEvent)
+so that, when selecting and copying whole KaTeX-rendered elements, the text
+content of the resulting clipboard renders KaTeX elements as their LaTeX source
+surrounded by specified delimiters.  (The HTML content of the resulting
+clipboard remains the selected HTML content, as it normally would.)
+The default delimiters are `$...$` for inline math and `$$...$$` for display
+math, but you can easy switch them to e.g. `\(...\)` and `\[...\]` by
+modifying `copyDelimiters` in [the source code](copy-tex.js).
+
+### Usage
+
+This extension isn't part of KaTeX proper, so the script should be separately
+included in the page.  It also provides *optional* custom CSS that
+defines KaTeX equations as
+[`user-select: all`](https://developer.mozilla.org/en-US/docs/Web/CSS/user-select)
+so that they get selected all-or-nothing (and thus trigger the good behavior
+provided by this extension).  Without this CSS, partially selected equations
+will just get the usual HTML copy/paste behavior.
+
+```html
+<link href="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.8.3/contrib/copy-tex.css" rel="stylesheet" type="text/css">
+<script src="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.8.3/contrib/copy-tex.min.js" integrity="sha384-RkgGHBDdR8eyBOoWeZ/vpGg1cOvSAJRflCUDACusAAIVwkwPrOUYykglPeqWakZu" crossorigin="anonymous"></script>
+```
+
+See [index.html](index.html) for an example.
+(To run this example from a clone of the repository, run `make serve`
+in the root KaTeX directory, and then visit
+http://0.0.0.0:7936/contrib/copy-tex/index.html
+with your web browser.)
+
+If you want to build your own custom copy handler based on this one,
+copy the `copy-tex.js` into your codebase and replace the `require`
+statement with `require('katex/contrib/copy-tex/katex2tex.js')`.
+
+### Known Issues
+
+This extension has been tested on Chrome, Firefox, Edge, and Safari.
+
+Microsoft Edge
+[does not seem to support](https://developer.microsoft.com/en-us/microsoft-edge/platform/status/clipboardapi/)
+text and HTML content in a single clipboard.  In this browser, this extension
+will just put the text content into the clipboard.
+
+Safari copies correctly, but the selection rectangle renders strangely
+(too big) when interacting with display math
+(because of the `user-select: all` CSS).

contrib/copy-tex/copy-tex.css

@@ -0,0 +1,12 @@
+/* Force selection of entire .katex/.katex-display blocks, so that we can
+ * copy/paste the entire source code.  If you omit this CSS, partial
+ * selections of a formula will work, but will copy the ugly HTML
+ * representation instead of the LaTeX source code.  (Full selections will
+ * still produce the LaTeX source code.)
+ */
+.katex, .katex-display {
+    user-select: all;
+    -moz-user-select: all;
+    -webkit-user-select: all;
+    -ms-user-select: all;
+}

contrib/copy-tex/copy-tex.js

@@ -0,0 +1,24 @@
+const katexReplaceWithTex = require('./katex2tex');
+
+// Global copy handler to modify behavior on .katex elements.
+document.addEventListener('copy', function(event) {
+    const selection = window.getSelection();
+    if (selection.isCollapsed) {
+        return;  // default action OK if selection is empty
+    }
+    const fragment = selection.getRangeAt(0).cloneContents();
+    if (!fragment.querySelector('.katex-mathml')) {
+        return;  // default action OK if no .katex-mathml elements
+    }
+    // Preserve usual HTML copy/paste behavior.
+    const html = [];
+    for (let i = 0; i < fragment.childNodes.length; i++) {
+        html.push(fragment.childNodes[i].outerHTML);
+    }
+    event.clipboardData.setData('text/html', html.join(''));
+    // Rewrite plain-text version.
+    event.clipboardData.setData('text/plain',
+        katexReplaceWithTex(fragment).textContent);
+    // Prevent normal copy handling.
+    event.preventDefault();
+});

contrib/copy-tex/index.html

@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<!--To run this example from a clone of the repository, run `make serve`
+    in the root KaTeX directory and then visit with your web browser:
+    http://0.0.0.0:7936/contrib/copy-tex/index.html
+  -->
+<html>
+  <head>
+    <meta charset="UTF-8">
+    <title>Copy-tex test</title>
+    <script src="/katex.js" type="text/javascript"></script>
+    <link href="/katex.css" rel="stylesheet" type="text/css">
+    <link href="./copy-tex.css" rel="stylesheet" type="text/css">
+    <script src="../auto-render/auto-render.js" type="text/javascript"></script>
+    <script src="./copy-tex.js" type="text/javascript"></script>
+    <style type="text/css">
+      body {
+          margin: 0px;
+          padding: 0px;
+          font-size: 36px;
+      }
+
+      #test > .blue {
+          color: blue;
+      }
+    </style>
+  </head>
+  <body>
+    <h1>Copy-tex test</h1>
+    <h2>Try copy/pasting some of the text below!</h2>
+    <p>
+    Here is some \(\KaTeX\) math: $$ x^2+y^2=z^2 $$
+    The variables are \(x\), \(y\), and \(z\),
+    which are all in \(\mathbb{R}^+\).
+    Q.E.D.
+    </p>
+    <script>
+      renderMathInElement(document.body);
+    </script>
+  </body>
+</html>

contrib/copy-tex/katex2tex.js

@@ -0,0 +1,52 @@
+// Set these to how you want inline and display math to be delimited.
+export const defaultCopyDelimiters = {
+    inline: ['$', '$'],    // alternative: ['\(', '\)']
+    display: ['$$', '$$'], // alternative: ['\[', '\]']
+};
+
+// Replace .katex elements with their TeX source (<annotation> element).
+// Modifies fragment in-place.  Useful for writing your own 'copy' handler,
+// as in copy-tex.js.
+export const katexReplaceWithTex = function(fragment,
+    copyDelimiters = defaultCopyDelimiters) {
+    // Remove .katex-html blocks that are preceded by .katex-mathml blocks
+    // (which will get replaced below).
+    const katexHtml = fragment.querySelectorAll('.katex-mathml + .katex-html');
+    for (let i = 0; i < katexHtml.length; i++) {
+        const element = katexHtml[i];
+        if (element.remove) {
+            element.remove(null);
+        } else {
+            element.parentNode.removeChild(element);
+        }
+    }
+    // Replace .katex-mathml elements with their annotation (TeX source)
+    // descendant, with inline delimiters.
+    const katexMathml = fragment.querySelectorAll('.katex-mathml');
+    for (let i = 0; i < katexMathml.length; i++) {
+        const element = katexMathml[i];
+        const texSource = element.querySelector('annotation');
+        if (texSource) {
+            if (element.replaceWith) {
+                element.replaceWith(texSource);
+            } else {
+                element.parentNode.replaceChild(texSource, element);
+            }
+            texSource.innerHTML = copyDelimiters.inline[0] +
+                texSource.innerHTML + copyDelimiters.inline[1];
+        }
+    }
+    // Switch display math to display delimiters.
+    const displays = fragment.querySelectorAll('.katex-display annotation');
+    for (let i = 0; i < displays.length; i++) {
+        const element = displays[i];
+        element.innerHTML = copyDelimiters.display[0] +
+            element.innerHTML.substr(copyDelimiters.inline[0].length,
+                element.innerHTML.length - copyDelimiters.inline[0].length
+                - copyDelimiters.inline[1].length)
+            + copyDelimiters.display[1];
+    }
+    return fragment;
+};
+
+module.exports = katexReplaceWithTex;