Add the [params] concept to front matter

hugolib/page__meta.go

@@ -421,9 +421,20 @@ func (p *pageState) setMetaPostParams() error {
 	var sitemapSet bool
 
 	var draft, published, isCJKLanguage *bool
+	var userParams map[string]any
 	for k, v := range pm.params {
 		loki := strings.ToLower(k)
 
+		if loki == "params" {
+			vv, err := maps.ToStringMapE(v)
+			if err != nil {
+				return err
+			}
+			userParams = vv
+			delete(pm.params, k)
+			continue
+		}
+
 		if loki == "published" { // Intentionally undocumented
 			vv, err := cast.ToBoolE(v)
 			if err == nil {
@@ -589,6 +600,10 @@ func (p *pageState) setMetaPostParams() error {
 		}
 	}
 
+	for k, v := range userParams {
+		pm.params[strings.ToLower(k)] = v
+	}
+
 	if !sitemapSet {
 		pm.sitemap = p.s.conf.Sitemap
 	}

hugolib/params_test.go

@@ -0,0 +1,54 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed 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
+// http://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.
+
+package hugolib
+
+import "testing"
+
+func TestFrontMatterParamsInItsOwnSection(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+baseURL = "https://example.org/"
+-- content/_index.md --
++++
+title = "Home"
+[[cascade]]
+background = 'yosemite.jpg'
+[cascade.params]
+a = "home-a"
+b = "home-b"
+[cascade._target]
+kind = 'page'
++++
+-- content/p1.md --
+---
+title: "P1"
+summary: "frontmatter.summary"
+params:
+   a: "p1-a"
+   summary: "params.summary"
+---	
+-- layouts/_default/single.html --
+Params: {{ range $k, $v := .Params }}{{ $k }}: {{ $v }}|{{ end }}$
+Summary: {{ .Summary }}|
+`
+
+	b := Test(t, files)
+
+	b.AssertFileContent("public/p1/index.html",
+		"Params: a: p1-a|b: home-b|background: yosemite.jpg|draft: false|iscjklanguage: false|summary: params.summary|title: P1|$",
+		"Summary: frontmatter.summary|",
+	)
+}

resources/page/page_matcher.go

@@ -144,7 +144,16 @@ func mapToPageMatcherParamsConfig(m map[string]any) (PageMatcherParamsConfig, er
 			// those values will now be moved to the top level.
 			// This should be very unlikely as it would lead to constructs like .Params.params.foo,
 			// and most people see params as an Hugo internal keyword.
-			pcfg.Params = maps.ToStringMap(v)
+			params := maps.ToStringMap(v)
+			if pcfg.Params == nil {
+				pcfg.Params = params
+			} else {
+				for k, v := range params {
+					if _, found := pcfg.Params[k]; !found {
+						pcfg.Params[k] = v
+					}
+				}
+			}
 		case "_target", "target":
 			var target PageMatcher
 			if err := decodePageMatcher(v, &target); err != nil {