Emit a warning that can be turned off when overwriting built-in .Para…

…ms values

Fixes #11941

common/constants/constants.go

@@ -13,12 +13,14 @@
 
 package constants
 
-// Error IDs.
+// Error/Warning IDs.
 // Do not change these values.
 const (
 	// IDs for remote errors in tpl/data.
 	ErrRemoteGetJSON = "error-remote-getjson"
 	ErrRemoteGetCSV  = "error-remote-getcsv"
+
+	WarnFrontMatterParamsOverrides = "warning-frontmatter-params-overrides"
 )
 
 // Field/method names with special meaning.

hugolib/page__meta.go

@@ -31,6 +31,7 @@ import (
 
 	"github.com/gohugoio/hugo/source"
 
+	"github.com/gohugoio/hugo/common/constants"
 	"github.com/gohugoio/hugo/common/hugo"
 	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/common/paths"
@@ -621,6 +622,9 @@ func (p *pageState) setMetaPostParams() error {
 	}
 
 	for k, v := range userParams {
+		if _, found := params[k]; found {
+			p.s.Log.Warnidf(constants.WarnFrontMatterParamsOverrides, "Hugo front matter key %q is overridden in params section.", k)
+		}
 		params[strings.ToLower(k)] = v
 	}
 

hugolib/params_test.go

@@ -133,6 +133,28 @@ RegularPages: {{ range site.RegularPages }}{{ .Path }}|{{ .RelPermalink }}|{{ .T
 	)
 }
 
+func TestFrontMatterTitleOverrideWarn(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+baseURL = "https://example.org/"
+disableKinds = ["taxonomy", "term"]
+-- content/p1.md --
+---
+title: "My title"
+params:
+  title: "My title from params"
+---
+
+
+`
+
+	b := Test(t, files, TestOptWarn())
+
+	b.AssertLogContains("ARN  Hugo front matter key \"title\" is overridden in params section", "You can suppress this warning")
+}
+
 func TestFrontMatterParamsLangNoCascade(t *testing.T) {
 	t.Parallel()