Move the shared ESLint plugin/config into the monorepo (#24670)

* Move the shared ESLint plugin/config into the monorepo

* Add peer dependencies to ESLint plugin

webapp/platform/eslint-plugin/rules/no-dispatch-getstate.js

@@ -0,0 +1,49 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+module.exports = {
+    meta: {
+        type: 'problem',
+        fixable: 'code',
+        messages: {
+            unexpected: 'Unexpected second argument passed to dispatch. getState does not need to be passed into dispatch.',
+        },
+    },
+    create(context) {
+        function checkDispatch(node) {
+            const args = node.arguments;
+            if (args.length === 2) {
+                context.report({
+                    node,
+                    messageId: 'unexpected',
+                    fix(fixer) {
+                        const sourceCode = context.getSourceCode();
+
+                        const before = sourceCode.getTokenBefore(args[1]);
+                        const after = sourceCode.getTokenAfter(args[1]);
+
+                        // Remove the getState argument and the preceding comma
+                        const fixes = [
+                            fixer.remove(before),
+                            fixer.remove(args[1]),
+                        ];
+
+                        // And remove the trailing comma if one exists
+                        if (after.type === 'Punctuator' && after.value === ',') {
+                            fixes.push(fixer.remove(after));
+                        }
+
+                        // Note that this sometimes mangles the whitespace slightly
+
+                        return fixes;
+                    },
+                });
+            }
+        }
+
+        return {
+            "CallExpression[callee.name='dispatch']": checkDispatch,
+            "CallExpression[callee.name='doDispatch']": checkDispatch,
+        };
+    },
+};

webapp/platform/eslint-plugin/rules/use-external-link.js

@@ -0,0 +1,43 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+const astUtils = require('jsx-ast-utils')
+const getElementType = require('eslint-plugin-jsx-a11y/lib/util/getElementType')
+
+module.exports =  {
+    meta: {
+        docs: {
+            description: 'Enforce all anchors with target="_blank" to use ExternalLink component',
+        },
+    },
+    create: (context) => {
+        const elementType = getElementType(context);
+        return {
+            JSXOpeningElement: (node) => {
+                const { attributes } = node;
+                const typeCheck = 'a';
+                const nodeType = elementType(node);
+                // Only check anchor elements
+                if (!nodeType || typeCheck !== nodeType) {
+                    return;
+                }
+
+                const propsToValidate = ['target'];
+                const values = propsToValidate.map((prop) => astUtils.getPropValue(astUtils.getProp(node.attributes, prop)));
+                // Checks if the target attribute is set to _blank (ie, is an external link)
+                const hasBlankTarget = values.some((value) => value != null && value === '_blank');
+
+                // When there is no target value at all, this rule does not apply:
+                if (!hasBlankTarget) {
+                    return;
+                }
+
+                context.report({
+                    node,
+                    message: 'Use ExternalLink component (components/external_link) for _blank target link-outs',
+                });
+                return
+            },
+        };
+    },
+};