g:flashMessages tag

grails-doc/src/en/guide/reference.adoc

@@ -1138,6 +1138,11 @@ include::ref/Tags/fieldValue.adoc[]
 
 include::ref/Tags/findAll.adoc[]
 
+[[ref-tags-flashMessages]]
+==== flashMessages
+
+include::ref/Tags/flashMessages.adoc[]
+
 [[ref-tags-form]]
 ==== form
 

grails-doc/src/en/guide/upgrading/upgrading71x.adoc

@@ -721,4 +721,25 @@ If this causes issues with existing URL mappings, you can disable it in `applica
 grails:
     urlmapping:
         validateWildcards: false
-----
+----
+
+===== 2.10 Flash Messages Tag (`g:flashMessages`)
+
+Grails 7.1 introduces a new `<g:flashMessages />` tag that renders `flash.message`, `flash.error`, and `flash.warning` as Bootstrap 5 dismissible alerts with appropriate styling (success, danger, and warning respectively).
+
+The tag automatically prevents duplicate rendering -- if called in both a page and its layout, only the first invocation produces output. All flash content is HTML-encoded to prevent XSS.
+
+The default layout (`main.gsp`) and all scaffolding templates now use this tag. If your application has custom views that render flash messages manually, you can replace the boilerplate:
+
+[source,xml]
+----
+<%-- Before --%>
+<g:if test="${flash.message}">
+    <div class="alert alert-primary" role="alert">${flash.message}</div>
+</g:if>
+
+<%-- After --%>
+<g:flashMessages />
+----
+
+The tag supports optional attributes for customizing CSS classes, icons, ARIA role, and dismissibility. See the {gspTagsRef}flashMessages.html[flashMessages] tag reference for full details.

grails-doc/src/en/ref/Tags - GSP/flashMessages.adoc

@@ -0,0 +1,120 @@
+////
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+////
+
+
+== flashMessages
+
+
+
+=== Purpose
+
+
+Renders `flash.message`, `flash.error`, and `flash.warning` as dismissible Bootstrap alert divs with appropriate styling. Automatically prevents duplicate rendering when used in both pages and layouts.
+
+
+=== Examples
+
+
+Basic usage in a view:
+
+[source,xml]
+----
+<g:flashMessages />
+----
+
+In a layout (safe to use alongside page-level usage -- the tag skips rendering if already called):
+
+[source,xml]
+----
+<g:flashMessages />
+<g:layoutBody/>
+----
+
+Non-dismissible alerts:
+
+[source,xml]
+----
+<g:flashMessages dismissible="false" />
+----
+
+Custom ARIA role:
+
+[source,xml]
+----
+<g:flashMessages role="status" />
+----
+
+Custom styling for success messages:
+
+[source,xml]
+----
+<g:flashMessages messageClass="alert alert-info" messageIcon="bi bi-info-circle me-2" />
+----
+
+Setting flash messages in a controller:
+
+[source,groovy]
+----
+// Success message (renders as green alert)
+flash.message = "Book '${book.title}' saved successfully."
+
+// Error message (renders as red alert)
+flash.error = "Unable to delete the record."
+
+// Warning message (renders as yellow alert)
+flash.warning = "You have unsaved changes."
+----
+
+
+=== Description
+
+
+The `flashMessages` tag renders any combination of `flash.message`, `flash.error`, and `flash.warning` as Bootstrap 5 alert divs. Each flash key maps to a different alert style:
+
+[cols="1,2,2"]
+|===
+| Flash Key | Default Alert Class | Default Icon
+
+| `flash.message`
+| `alert alert-success alert-dismissible fade show`
+| `bi bi-check-circle me-2`
+
+| `flash.error`
+| `alert alert-danger alert-dismissible fade show`
+| `bi bi-exclamation-triangle me-2`
+
+| `flash.warning`
+| `alert alert-warning alert-dismissible fade show`
+| `bi bi-exclamation-circle me-2`
+|===
+
+The tag automatically sets a `_flashRendered` request attribute after rendering. On subsequent calls within the same request, the tag detects this attribute and outputs nothing. This allows both pages and layouts to include `<g:flashMessages />` without producing duplicate alerts -- whichever renders first wins.
+
+All flash message content is HTML-encoded to prevent XSS.
+
+Attributes
+
+* `messageClass` (optional) - CSS class for `flash.message` alerts. Default: `alert alert-success alert-dismissible fade show`
+* `messageIcon` (optional) - Icon class for `flash.message` alerts. Default: `bi bi-check-circle me-2`
+* `errorClass` (optional) - CSS class for `flash.error` alerts. Default: `alert alert-danger alert-dismissible fade show`
+* `errorIcon` (optional) - Icon class for `flash.error` alerts. Default: `bi bi-exclamation-triangle me-2`
+* `warningClass` (optional) - CSS class for `flash.warning` alerts. Default: `alert alert-warning alert-dismissible fade show`
+* `warningIcon` (optional) - Icon class for `flash.warning` alerts. Default: `bi bi-exclamation-circle me-2`
+* `role` (optional) - ARIA role for alert divs. Default: `alert`
+* `dismissible` (optional) - Whether to show a close button. Default: `true`

grails-forge/grails-forge-core/src/main/resources/gsp/main.gsp

@@ -21,6 +21,7 @@
 
 <div class="bg-body-tertiary">
     <div class="container-lg py-4">
+        <g:flashMessages />
         <g:layoutBody/>
     </div>
 </div>

grails-gsp/plugin/src/main/groovy/org/grails/plugins/web/taglib/ApplicationTagLib.groovy

@@ -471,4 +471,68 @@ class ApplicationTagLib implements ApplicationContextAware, InitializingBean, Gr
         // encoding is handled in GroovyPage.invokeTag and GroovyPage.captureTagOutput
         body()
     }
+
+    /**
+     * Renders flash.message, flash.error, and flash.warning as Bootstrap alert divs.
+     * Automatically skips rendering if already called during this request, preventing
+     * duplicate display when used in both pages and layouts.
+     *
+     * @emptyTag
+     *
+     * @attr messageClass CSS class for flash.message alerts (default: 'alert alert-success alert-dismissible fade show')
+     * @attr messageIcon Icon class for flash.message alerts (default: 'bi bi-check-circle me-2')
+     * @attr errorClass CSS class for flash.error alerts (default: 'alert alert-danger alert-dismissible fade show')
+     * @attr errorIcon Icon class for flash.error alerts (default: 'bi bi-exclamation-triangle me-2')
+     * @attr warningClass CSS class for flash.warning alerts (default: 'alert alert-warning alert-dismissible fade show')
+     * @attr warningIcon Icon class for flash.warning alerts (default: 'bi bi-exclamation-circle me-2')
+     * @attr role ARIA role for alert divs (default: 'alert')
+     * @attr dismissible Whether to show a close button (default: true)
+     */
+    Closure flashMessages = { attrs ->
+        if (request.getAttribute('_flashRendered')) {
+            return
+        }
+
+        boolean rendered = false
+        boolean dismissible = attrs.dismissible != null ? attrs.dismissible.toString().toBoolean() : true
+        String role = attrs.role ?: 'alert'
+
+        if (flash.message) {
+            renderFlashAlert(
+                    attrs.messageClass ?: 'alert alert-success alert-dismissible fade show',
+                    attrs.messageIcon ?: 'bi bi-check-circle me-2',
+                    flash.message, dismissible, role)
+            rendered = true
+        }
+
+        if (flash.error) {
+            renderFlashAlert(
+                    attrs.errorClass ?: 'alert alert-danger alert-dismissible fade show',
+                    attrs.errorIcon ?: 'bi bi-exclamation-triangle me-2',
+                    flash.error, dismissible, role)
+            rendered = true
+        }
+
+        if (flash.warning) {
+            renderFlashAlert(
+                    attrs.warningClass ?: 'alert alert-warning alert-dismissible fade show',
+                    attrs.warningIcon ?: 'bi bi-exclamation-circle me-2',
+                    flash.warning, dismissible, role)
+            rendered = true
+        }
+
+        if (rendered) {
+            request.setAttribute('_flashRendered', true)
+        }
+    }
+
+    private void renderFlashAlert(String cssClass, String icon, Object message, boolean dismissible, String role) {
+        out << "<div class=\"${cssClass}\" role=\"${role}\">"
+        out << "<i class=\"${icon}\"></i>"
+        out << message.toString().encodeAsHTML()
+        if (dismissible) {
+            out << '<button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>'
+        }
+        out << '</div>'
+    }
 }

grails-profiles/web/skeleton/grails-app/views/layouts/main.gsp

@@ -21,6 +21,7 @@
 
 <div class="bg-body-tertiary">
     <div class="container-lg py-4">
+        <g:flashMessages />
         <g:layoutBody/>
     </div>
 </div>

grails-scaffolding/src/main/templates/scaffolding/create.gsp

@@ -24,9 +24,7 @@
         <section class="row">
             <div id="create-${propertyName}" class="col-12 content scaffold-create" role="main">
                 <h1><g:message code="default.create.label" args="[entityName]" /></h1>
-                <g:if test="\${flash.message}">
-                    <div class="message" role="status">\${flash.message}</div>
-                </g:if>
+                <g:flashMessages />
                 <g:hasErrors bean="\${this.${propertyName}}">
                     <ul class="alert alert-danger list-unstyled" role="alert">
                         <g:eachError bean="\${this.${propertyName}}" var="error">

grails-scaffolding/src/main/templates/scaffolding/edit.gsp

@@ -27,9 +27,7 @@
         <section class="row">
             <div id="edit-${propertyName}" class="col-12 content scaffold-edit" role="main">
                 <h1><g:message code="default.edit.label" args="[entityName]" /></h1>
-                <g:if test="\${flash.message}">
-                    <div class="message" role="status">\${flash.message}</div>
-                </g:if>
+                <g:flashMessages />
                 <g:hasErrors bean="\${this.${propertyName}}">
                     <ul class="alert alert-danger list-unstyled" role="alert">
                         <g:eachError bean="\${this.${propertyName}}" var="error">

grails-scaffolding/src/main/templates/scaffolding/index.gsp

@@ -25,9 +25,7 @@
             <div id="list-\${propertyName}" class="col-12 content scaffold-list" role="main">
                 <h1>
                     <g:message code="default.list.label" args="[entityName]" /></h1>
-                <g:if test="\${flash.message}">
-                    <div class="alert alert-primary" role="alert"><i class="bi-info-circle"></i> \${flash.message}</div>
-                </g:if>
+                <g:flashMessages />
                 <f:table class="scaffold table table-striped table-sm" controller="\${controllerName}" collection="\${${propertyName}List}"/>
 
                 <g:if test="\${${propertyName}Count > params.int('max')}">

grails-scaffolding/src/main/templates/scaffolding/show.gsp

@@ -27,9 +27,7 @@
         <section class="row">
             <div id="show-${propertyName}" class="col-12 content scaffold-show" role="main">
                 <h1><g:message code="default.show.label" args="[entityName]" /></h1>
-                <g:if test="\${flash.message}">
-                    <div class="alert alert-primary" role="alert"><i class="bi-info-circle"></i> \${flash.message}</div>
-                </g:if>
+                <g:flashMessages />
                 <f:display bean="${propertyName}" listClass="container" listItemClass="row mb-3" labelClass="form-label col-sm-3 text-sm-end" valueClass="col-sm-9" />
                 <g:form resource="\${this.${propertyName}}" controller="\${controllerName}" method="DELETE">
                     <fieldset class="bg-body-tertiary">