tpl/collections: Include template path in IsSet unsupported type warning

When isset is called on a value that's not an array, channel, slice, or
map, Hugo logs a warning that says only "calling IsSet with unsupported
type X (Y) will always return false." On any site with more than one
template, there's no way to find the offending call site.

Thread context through IsSet and surface the executing template's
filename in the warning. Switch from Log.Warnf to Log.Warnidf so the
warning is grouped under an ID that users can suppress via ignoreLogs.

Fixes #11794

Author: truffle-dev

common/constants/constants.go

@@ -20,6 +20,7 @@ const (
 	WarnGoldmarkRawHTML          = "warning-goldmark-raw-html"
 	WarnPartialSuperfluousPrefix = "warning-partial-superfluous-prefix"
 	WarnHomePageIsLeafBundle     = "warning-home-page-is-leaf-bundle"
+	WarnIsSetUnsupportedType     = "warning-isset-unsupported-type"
 )
 
 // Field/method names with special meaning.

docs/data/docs.yaml

@@ -2376,6 +2376,7 @@ tpl:
         - isSet
         - isset
         Args:
+        - ctx
         - c
         - key
         Description: |-

tpl/collections/collections.go

@@ -20,17 +20,20 @@ import (
 	"errors"
 	"fmt"
 	"math/rand/v2"
+	"path/filepath"
 	"reflect"
 	"strings"
 	"time"
 
 	"github.com/gohugoio/hugo/common/collections"
+	"github.com/gohugoio/hugo/common/constants"
 	"github.com/gohugoio/hugo/common/hmaps"
 	"github.com/gohugoio/hugo/common/hreflect"
 	"github.com/gohugoio/hugo/common/hstore"
 	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/langs"
+	"github.com/gohugoio/hugo/tpl"
 	"github.com/gohugoio/hugo/tpl/compare"
 	"github.com/spf13/cast"
 )
@@ -339,7 +342,7 @@ func (ns *Namespace) Group(key any, items any) (any, error) {
 
 // IsSet returns whether a given array, channel, slice, or map in c has the given key
 // defined.
-func (ns *Namespace) IsSet(c any, key any) (bool, error) {
+func (ns *Namespace) IsSet(ctx context.Context, c any, key any) (bool, error) {
 	av := reflect.ValueOf(c)
 	kv := reflect.ValueOf(key)
 
@@ -357,7 +360,15 @@ func (ns *Namespace) IsSet(c any, key any) (bool, error) {
 			return av.MapIndex(kv).IsValid(), nil
 		}
 	default:
-		ns.deps.Log.Warnf("calling IsSet with unsupported type %q (%T) will always return false.\n", av.Kind(), c)
+		var where string
+		if currentTpl := tpl.Context.CurrentTemplate.Get(ctx); currentTpl != nil {
+			if f := currentTpl.Filename(); f != "" {
+				where = fmt.Sprintf(" in %q", filepath.ToSlash(f))
+			} else if n := currentTpl.Name(); n != "" {
+				where = fmt.Sprintf(" in template %q", n)
+			}
+		}
+		ns.deps.Log.Warnidf(constants.WarnIsSetUnsupportedType, "calling IsSet with unsupported type %q (%T)%s will always return false.", av.Kind(), c, where)
 	}
 
 	return false, nil

tpl/collections/collections_integration_test.go

@@ -671,3 +671,20 @@ index: {{ index $d "foo" }}|
 
 	hugolib.Test(t, files).AssertFileContent("public/index.html", "dict: map[string]interface {} true 0", "! FAIL", "index: |", "d3: map[foo:bar]|")
 }
+
+// Issue 11794
+func TestIsSetUnsupportedTypeWarningIncludesTemplatePath(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['page','rss','section','sitemap','taxonomy','term']
+-- layouts/home.html --
+{{ $s := "hello" }}
+{{ if isset $s "anyKey" }}A{{ else }}B{{ end }}
+`
+
+	b := hugolib.Test(t, files, hugolib.TestOptWarn())
+
+	b.AssertLogContains(`WARN  calling IsSet with unsupported type "string" (string) in "/layouts/home.html" will always return false.`)
+}

tpl/collections/collections_test.go

@@ -460,7 +460,7 @@ func TestIsSet(t *testing.T) {
 	} {
 		errMsg := qt.Commentf("[%d] %v", i, test)
 
-		result, err := ns.IsSet(test.a, test.key)
+		result, err := ns.IsSet(context.Background(), test.a, test.key)
 		if test.isErr {
 			continue
 		}