markup: Standardize behavior when external converters are missing

Closes #14222

markup/asciidocext/internal/converter.go

@@ -87,9 +87,8 @@ func (a *AsciiDocConverter) Supports(_ identity.Identity) bool {
 // GetAsciiDocContent calls asciidoctor as an external helper to convert
 // AsciiDoc content to HTML.
 func (a *AsciiDocConverter) GetAsciiDocContent(src []byte, ctx converter.DocumentContext) ([]byte, error) {
-	if ok, err := HasAsciiDoc(); !ok {
-		a.Cfg.Logger.Errorf("leaving AsciiDoc content unrendered: %s", err.Error())
-		return src, nil
+	if !hexec.InPath(asciiDocBinaryName) {
+		return nil, fmt.Errorf("asciidoctor not found in $PATH, cannot render %q", ctx.DocumentName)
 	}
 
 	args, err := a.ParseArgs(ctx)

markup/pandoc/convert.go

@@ -15,6 +15,8 @@
 package pandoc
 
 import (
+	"fmt"
+
 	"github.com/gohugoio/hugo/common/hexec"
 	"github.com/gohugoio/hugo/htesting"
 	"github.com/gohugoio/hugo/identity"
@@ -56,12 +58,9 @@ func (c *pandocConverter) Supports(feature identity.Identity) bool {
 
 // getPandocContent calls pandoc as an external helper to convert pandoc markdown to HTML.
 func (c *pandocConverter) getPandocContent(src []byte, ctx converter.DocumentContext) ([]byte, error) {
-	logger := c.cfg.Logger
 	binaryName := getPandocBinaryName()
 	if binaryName == "" {
-		logger.Println("pandoc not found in $PATH: Please install.\n",
-			"                 Leaving pandoc content unrendered.")
-		return src, nil
+		return nil, fmt.Errorf("pandoc not found in $PATH, cannot render %q", ctx.DocumentName)
 	}
 	args := []string{"--mathjax"}
 	return internal.ExternallyRenderContent(c.cfg, ctx, src, binaryName, args)

markup/rst/convert.go

@@ -16,6 +16,7 @@ package rst
 
 import (
 	"bytes"
+	"fmt"
 	"runtime"
 
 	"github.com/gohugoio/hugo/common/hexec"
@@ -65,9 +66,7 @@ func (c *rstConverter) getRstContent(src []byte, ctx converter.DocumentContext)
 	binaryName, binaryPath := getRstBinaryNameAndPath()
 
 	if binaryName == "" {
-		logger.Println("rst2html / rst2html.py not found in $PATH: Please install.\n",
-			"                 Leaving reStructuredText content unrendered.")
-		return src, nil
+		return nil, fmt.Errorf("rst2html / rst2html.py not found in $PATH, cannot render %q", ctx.DocumentName)
 	}
 
 	logger.Infoln("Rendering", ctx.DocumentName, "with", binaryName, "...")