new: [CodeMirror] Shows a placeholder whenever the textarea is empty

templates/layout/default.php

@@ -52,6 +52,7 @@ $sidebarOpen = $loggedUser->user_settings_by_name_with_fallback['ui.sidebar.expa
     <?= $this->Html->script('CodeMirror/addon/lint/json-lint') ?>
     <?= $this->Html->script('CodeMirror/addon/edit/matchbrackets') ?>
     <?= $this->Html->script('CodeMirror/addon/edit/closebrackets') ?>
+    <?= $this->Html->script('CodeMirror/addon/display/placeholder') ?>
     <?= $this->Html->css('CodeMirror/codemirror') ?>
     <?= $this->Html->css('CodeMirror/codemirror-additional') ?>
     <?= $this->Html->css('CodeMirror/addon/hint/show-hint') ?>

webroot/css/CodeMirror/codemirror-additional.css

@@ -26,4 +26,8 @@
 
 .CodeMirror-hints {
     z-index: 1060 !important; /* Make sure hint is above modal */
+}
+
+.CodeMirror pre.CodeMirror-placeholder {
+    color: #999; 
 }

webroot/js/CodeMirror/addon/display/placeholder.js

@@ -0,0 +1,78 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: https://codemirror.net/LICENSE
+
+(function (mod) {
+    if (typeof exports == "object" && typeof module == "object") // CommonJS
+        mod(require("../../lib/codemirror"));
+    else if (typeof define == "function" && define.amd) // AMD
+        define(["../../lib/codemirror"], mod);
+    else // Plain browser env
+        mod(CodeMirror);
+})(function (CodeMirror) {
+    CodeMirror.defineOption("placeholder", "", function (cm, val, old) {
+        var prev = old && old != CodeMirror.Init;
+        if (val && !prev) {
+            cm.on("blur", onBlur);
+            cm.on("change", onChange);
+            cm.on("swapDoc", onChange);
+            CodeMirror.on(cm.getInputField(), "compositionupdate", cm.state.placeholderCompose = function () { onComposition(cm) })
+            onChange(cm);
+        } else if (!val && prev) {
+            cm.off("blur", onBlur);
+            cm.off("change", onChange);
+            cm.off("swapDoc", onChange);
+            CodeMirror.off(cm.getInputField(), "compositionupdate", cm.state.placeholderCompose)
+            clearPlaceholder(cm);
+            var wrapper = cm.getWrapperElement();
+            wrapper.className = wrapper.className.replace(" CodeMirror-empty", "");
+        }
+
+        if (val && !cm.hasFocus()) onBlur(cm);
+    });
+
+    function clearPlaceholder(cm) {
+        if (cm.state.placeholder) {
+            cm.state.placeholder.parentNode.removeChild(cm.state.placeholder);
+            cm.state.placeholder = null;
+        }
+    }
+    function setPlaceholder(cm) {
+        clearPlaceholder(cm);
+        var elt = cm.state.placeholder = document.createElement("pre");
+        elt.style.cssText = "height: 0; overflow: visible";
+        elt.style.direction = cm.getOption("direction");
+        elt.className = "CodeMirror-placeholder CodeMirror-line-like";
+        var placeHolder = cm.getOption("placeholder")
+        if (typeof placeHolder == "string") placeHolder = document.createTextNode(placeHolder)
+        elt.appendChild(placeHolder)
+        cm.display.lineSpace.insertBefore(elt, cm.display.lineSpace.firstChild);
+    }
+
+    function onComposition(cm) {
+        setTimeout(function () {
+            var empty = false
+            if (cm.lineCount() == 1) {
+                var input = cm.getInputField()
+                empty = input.nodeName == "TEXTAREA" ? !cm.getLine(0).length
+                    : !/[^\u200b]/.test(input.querySelector(".CodeMirror-line").textContent)
+            }
+            if (empty) setPlaceholder(cm)
+            else clearPlaceholder(cm)
+        }, 20)
+    }
+
+    function onBlur(cm) {
+        if (isEmpty(cm)) setPlaceholder(cm);
+    }
+    function onChange(cm) {
+        var wrapper = cm.getWrapperElement(), empty = isEmpty(cm);
+        wrapper.className = wrapper.className.replace(" CodeMirror-empty", "") + (empty ? " CodeMirror-empty" : "");
+
+        if (empty) setPlaceholder(cm);
+        else clearPlaceholder(cm);
+    }
+
+    function isEmpty(cm) {
+        return (cm.lineCount() === 1) && (cm.getLine(0) === "");
+    }
+});