tpl: Narrow down the usage of plain text shortcodes when rendering HTML

After this commit, if you want to resolve `layouts/_shortcodes/myshortcode.txt` when rendering HTML content, you need to use the `{{%` shortcode delimiter:

```
{{% myshortcode %}}
```

This should be what people would do anyway, but we have also as part of this improved the error message to inform about what needs to be done.

Note that this is not relevant for partials.

Fixes #13698

hugolib/shortcode.go

@@ -398,6 +398,10 @@ func doRenderShortcode(
 			return true
 		}
 		base, layoutDescriptor := po.GetInternalTemplateBasePathAndDescriptor()
+
+		// With shortcodes/mymarkdown.md (only), this allows {{% mymarkdown %}} when rendering HTML,
+		// but will not resolve any template when doing {{< mymarkdown >}}.
+		layoutDescriptor.AlwaysAllowPlainText = sc.doMarkup
 		q := tplimpl.TemplateQuery{
 			Path:     base,
 			Name:     sc.name,
@@ -405,10 +409,9 @@ func doRenderShortcode(
 			Desc:     layoutDescriptor,
 			Consider: include,
 		}
-		v := s.TemplateStore.LookupShortcode(q)
+		v, err := s.TemplateStore.LookupShortcode(q)
 		if v == nil {
-			s.Log.Errorf("Unable to locate template for shortcode %q in page %q", sc.name, p.File().Path())
-			return zeroShortcode, nil
+			return zeroShortcode, err
 		}
 		tmpl = v
 		hasVariants = hasVariants || len(ofCount) > 1

hugolib/shortcode_test.go

@@ -918,7 +918,7 @@ func TestShortcodeMarkdownOutputFormat(t *testing.T) {
 ---
 title: "p1"
 ---
-{{< foo >}}
+{{% foo %}}
 # The below would have failed using the HTML template parser.
 -- layouts/shortcodes/foo.md --
 §§§
@@ -930,9 +930,7 @@ title: "p1"
 
 	b := Test(t, files)
 
-	b.AssertFileContent("public/p1/index.html", `
-<x
-	`)
+	b.AssertFileContent("public/p1/index.html", "<code>&lt;x")
 }
 
 func TestShortcodePreserveIndentation(t *testing.T) {

tpl/tplimpl/shortcodes_integration_test.go

@@ -17,6 +17,7 @@ import (
 	"strings"
 	"testing"
 
+	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/htesting/hqt"
 	"github.com/gohugoio/hugo/hugolib"
 )
@@ -696,3 +697,35 @@ title: p2
 	b.AssertFileContent("public/p1/index.html", "78eb19b5c6f3768f")
 	b.AssertFileContent("public/p2/index.html", "a6db910a9cf54bc1")
 }
+
+func TestShortcodePlainTextVsHTMLTemplateIssue13698(t *testing.T) {
+	t.Parallel()
+
+	filesTemplate := `
+-- hugo.toml --
+markup.goldmark.renderer.unsafe = true
+-- layouts/all.html --
+Content: {{ .Content }}|
+-- layouts/_shortcodes/mymarkdown.md --
+<div>Foo bar</div>
+-- content/p1.md --
+---
+title: p1
+---
+## A shortcode
+
+SHORTCODE
+
+`
+
+	files := strings.ReplaceAll(filesTemplate, "SHORTCODE", "{{% mymarkdown %}}")
+	b := hugolib.Test(t, files)
+	b.AssertFileContent("public/p1/index.html", "<div>Foo bar</div>")
+
+	files = strings.ReplaceAll(filesTemplate, "SHORTCODE", "{{< mymarkdown >}}")
+
+	var err error
+	b, err = hugolib.TestE(t, files)
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, `no compatible template found for shortcode "mymarkdown" in [/_shortcodes/mymarkdown.md]; note that to use plain text template shortcodes in HTML you need to use the shortcode {{% delimiter`)
+}

tpl/tplimpl/templatedescriptor.go

@@ -37,6 +37,7 @@ type TemplateDescriptor struct {
 	// Misc.
 	LayoutFromUserMustMatch bool // If set, we only look for the exact layout.
 	IsPlainText             bool // Whether this is a plain text template.
+	AlwaysAllowPlainText    bool // Whether to e.g. allow plain text templates to be rendered in HTML.
 }
 
 func (d *TemplateDescriptor) normalizeFromFile() {
@@ -64,7 +65,7 @@ func (s descriptorHandler) compareDescriptors(category Category, isEmbedded bool
 		return weightNoMatch
 	}
 
-	w := this.doCompare(category, isEmbedded, s.opts.DefaultContentLanguage, other)
+	w := this.doCompare(category, s.opts.DefaultContentLanguage, other)
 
 	if w.w1 <= 0 {
 		if category == CategoryMarkup && (this.Variant1 == other.Variant1) && (this.Variant2 == other.Variant2 || this.Variant2 != "" && other.Variant2 == "") {
@@ -74,7 +75,12 @@ func (s descriptorHandler) compareDescriptors(category Category, isEmbedded bool
 			}
 
 			w.w1 = 1
-			return w
+		}
+
+		if category == CategoryShortcode {
+			if (this.IsPlainText == other.IsPlainText || !other.IsPlainText) || this.AlwaysAllowPlainText {
+				w.w1 = 1
+			}
 		}
 	}
 
@@ -82,13 +88,16 @@ func (s descriptorHandler) compareDescriptors(category Category, isEmbedded bool
 }
 
 //lint:ignore ST1006 this vs other makes it easier to reason about.
-func (this TemplateDescriptor) doCompare(category Category, isEmbedded bool, defaultContentLanguage string, other TemplateDescriptor) weight {
+func (this TemplateDescriptor) doCompare(category Category, defaultContentLanguage string, other TemplateDescriptor) weight {
 	w := weightNoMatch
 
+	if !this.AlwaysAllowPlainText {
 		// HTML in plain text is OK, but not the other way around.
 		if other.IsPlainText && !this.IsPlainText {
 			return w
 		}
+	}
+
 	if other.Kind != "" && other.Kind != this.Kind {
 		return w
 	}

tpl/tplimpl/templatestore.go

@@ -19,6 +19,7 @@ import (
 	"bytes"
 	"context"
 	"embed"
+	"errors"
 	"fmt"
 	"io"
 	"io/fs"
@@ -608,7 +609,7 @@ func (s *TemplateStore) LookupShortcodeByName(name string) *TemplInfo {
 	return ti
 }
 
-func (s *TemplateStore) LookupShortcode(q TemplateQuery) *TemplInfo {
+func (s *TemplateStore) LookupShortcode(q TemplateQuery) (*TemplInfo, error) {
 	q.init()
 	k1 := s.key(q.Path)
 
@@ -630,13 +631,15 @@ func (s *TemplateStore) LookupShortcode(q TemplateQuery) *TemplInfo {
 		}
 
 		for k, vv := range v {
+			best.candidates = append(best.candidates, vv)
 			if !q.Consider(vv) {
 				continue
 			}
 
 			weight := s.dh.compareDescriptors(q.Category, vv.subCategory == SubCategoryEmbedded, q.Desc, k)
 			weight.distance = distance
-			if best.isBetter(weight, vv) {
+			isBetter := best.isBetter(weight, vv)
+			if isBetter {
 				best.updateValues(weight, k2, k, vv)
 			}
 		}
@@ -644,8 +647,21 @@ func (s *TemplateStore) LookupShortcode(q TemplateQuery) *TemplInfo {
 		return false, nil
 	})
 
-	// Any match will do.
-	return best.templ
+	if best.w.w1 <= 0 {
+		var err error
+		if s := best.candidatesAsStringSlice(); s != nil {
+			msg := fmt.Sprintf("no compatible template found for shortcode %q in %s", q.Name, s)
+			if !q.Desc.IsPlainText {
+				msg += "; note that to use plain text template shortcodes in HTML you need to use the shortcode {{% delimiter"
+			}
+			err = errors.New(msg)
+		} else {
+			err = fmt.Errorf("no template found for shortcode %q", q.Name)
+		}
+		return nil, err
+	}
+
+	return best.templ, nil
 }
 
 // PrintDebug is for testing/debugging only.
@@ -1821,6 +1837,7 @@ type bestMatch struct {
 	desc       TemplateDescriptor
 	w          weight
 	key        string
+	candidates []*TemplInfo
 
 	// settings.
 	defaultOutputformat string
@@ -1831,6 +1848,18 @@ func (best *bestMatch) reset() {
 	best.w = weight{}
 	best.desc = TemplateDescriptor{}
 	best.key = ""
+	best.candidates = nil
+}
+
+func (best *bestMatch) candidatesAsStringSlice() []string {
+	if len(best.candidates) == 0 {
+		return nil
+	}
+	candidates := make([]string, len(best.candidates))
+	for i, v := range best.candidates {
+		candidates[i] = v.PathInfo.Path()
+	}
+	return candidates
 }
 
 func (best *bestMatch) isBetter(w weight, ti *TemplInfo) bool {
@@ -1840,7 +1869,6 @@ func (best *bestMatch) isBetter(w weight, ti *TemplInfo) bool {
 	}
 
 	if w.w1 <= 0 {
-
 		if best.w.w1 <= 0 {
 			return ti.PathInfo.Path() < best.templ.PathInfo.Path()
 		}

tpl/tplimpl/templatestore_integration_test.go

@@ -920,6 +920,26 @@ func TestPartialHTML(t *testing.T) {
 	b.AssertFileContent("public/index.html", "<link rel=\"stylesheet\" href=\"/css/style.css\">")
 }
 
+func TestPartialPlainTextInHTML(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+-- layouts/all.html --
+<html>
+<head>
+{{ partial "mypartial.txt" . }}
+</head>
+</html>
+-- layouts/partials/mypartial.txt --
+My <div>partial</div>.
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html", "My &lt;div&gt;partial&lt;/div&gt;.")
+}
+
 // Issue #13593.
 func TestGoatAndNoGoat(t *testing.T) {
 	t.Parallel()
@@ -1103,6 +1123,18 @@ All.
 	b.AssertLogContains("unrecognized render hook")
 }
 
+func TestLayoutNotFound(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+-- layouts/single.html --
+Single.
+`
+	b := hugolib.Test(t, files, hugolib.TestOptWarn())
+	b.AssertLogContains("WARN  found no layout file for \"html\" for kind \"home\"")
+}
+
 func TestLayoutOverrideThemeWhenThemeOnOldFormatIssue13715(t *testing.T) {
 	t.Parallel()
 
@@ -1214,8 +1246,8 @@ s2.
 			Category: tplimpl.CategoryShortcode,
 			Desc:     desc,
 		}
-		v := store.LookupShortcode(q)
-		if v == nil {
+		v, err := store.LookupShortcode(q)
+		if v == nil || err != nil {
 			b.Fatal("not found")
 		}
 	}