fix: stop empty output from containers wrongly treated as hidden

README.md

@@ -48,9 +48,12 @@ myPlaintext, err := textplain.Convert(myHTML,
 | `WithLinks(style)` | `LinksInline` |
 | `WithPlainHeadings()` | off, so headings are drawn with rule characters |
 | `WithMarkdown()` | off; renders CommonMark instead of plain text |
+| `WithHiddenContent()` | off, so content hidden by inline styles or attributes is dropped |
 
 Later options win, so a caller can layer its own on top of a shared set.
 
+Hidden content is judged from inline styles, so a layout can occasionally convert to an empty string. Callers that need text can retry with `WithHiddenContent()`.
+
 `WithLinks` takes one of three styles:
 
 | style | `<a href="https://example.com">Docs</a>` becomes |

options.go

@@ -26,6 +26,7 @@ type options struct {
 	links         LinkStyle
 	plainHeadings bool
 	markdown      bool
+	hiddenContent bool
 }
 
 func newOptions(opts []Option) options {
@@ -74,6 +75,12 @@ func WithPlainHeadings() Option {
 	return func(o *options) { o.plainHeadings = true }
 }
 
+// WithHiddenContent keeps content that inline styles or attributes hide, such
+// as preheaders.
+func WithHiddenContent() Option {
+	return func(o *options) { o.hiddenContent = true }
+}
+
 // WithMarkdown renders CommonMark instead of plain text. Output is not wrapped,
 // so WithLineLength and WithPlainHeadings have no effect, and any WithBullet or
 // WithOrderedSuffix must be a Markdown list marker.

options_test.go

@@ -82,6 +82,18 @@ func TestOptionsDefaultToTheDefaultLineLength(t *testing.T) {
 	}
 }
 
+func TestOptionsHiddenContent(t *testing.T) {
+	body := `<div style="display:none"><p>only content</p></div>`
+
+	result, err := textplain.Convert(body)
+	require.NoError(t, err)
+	assert.Empty(t, result)
+
+	result, err = textplain.Convert(body, textplain.WithHiddenContent())
+	require.NoError(t, err)
+	assert.Equal(t, "only content", result)
+}
+
 func TestOptionsFootnotesSkipEmptyLinks(t *testing.T) {
 	result, err := textplain.Convert(`<p>text<a href="https://a.example"></a></p>`, textplain.WithLinks(textplain.LinksFootnotes))
 	require.NoError(t, err)

textplain_test.go

@@ -951,13 +951,8 @@ func TestHiddenContent(t *testing.T) {
 			expect: "shown",
 		},
 		testCase{
-			name:   "zero font size with a unit",
-			body:   `<p>shown</p><p style="font-size:0px">hidden</p>`,
-			expect: "shown",
-		},
-		testCase{
-			name:   "zero max height",
-			body:   `<p>shown</p><p style="max-height:0">hidden</p>`,
+			name:   "zero max height with overflow hidden",
+			body:   `<p>shown</p><p style="max-height:0px;overflow:hidden">hidden</p>`,
 			expect: "shown",
 		},
 		testCase{
@@ -1001,6 +996,16 @@ func TestHiddenContent(t *testing.T) {
 			body:   `<p>shown</p><p style="font-size:0.9em">still visible</p>`,
 			expect: "shown\n\nstill visible",
 		},
+		testCase{
+			name:   "zero font size container with sized children stays visible",
+			body:   `<div style="font-size:0"><table style="display:inline-block"><tr><td style="font-size:16px">still visible</td></tr></table></div>`,
+			expect: "still visible",
+		},
+		testCase{
+			name:   "zero max height without overflow hidden stays visible",
+			body:   `<div style="max-height:0"><p>still visible</p></div>`,
+			expect: "still visible",
+		},
 		testCase{
 			name:   "aria-hidden false stays visible",
 			body:   `<p>shown</p><p aria-hidden="false">still visible</p>`,

tree.go

@@ -65,6 +65,10 @@ type conversion struct {
 // Convert renders the body of document as plain text, wrapping at
 // DefaultLineLength unless an option says otherwise. It returns
 // ErrBodyNotFound if the document has no body.
+//
+// The result is empty when the body has no visible text, which can mean
+// hidden content was misjudged; callers that need text can retry with
+// WithHiddenContent.
 func Convert(document string, opts ...Option) (string, error) {
 	return ConvertReader(strings.NewReader(document), opts...)
 }
@@ -77,13 +81,13 @@ func ConvertReader(r io.Reader, opts ...Option) (string, error) {
 		return "", err
 	}
 
-	cv := &conversion{opts: newOptions(opts)}
-
 	body := findBody(root)
 	if body == nil {
 		return "", ErrBodyNotFound
 	}
 
+	cv := &conversion{opts: newOptions(opts)}
+
 	var o output
 
 	cv.doConvert(&o, body)
@@ -190,7 +194,7 @@ func (cv *conversion) doConvert(o *output, n *html.Node) {
 				continue
 			}
 
-			if isHidden(c) {
+			if cv.isHidden(c) {
 				continue
 			}
 
@@ -730,7 +734,7 @@ func (cv *conversion) listItems(o *output, n *html.Node, prefixer func(int) stri
 	idx := listStart(n)
 
 	for c := n.FirstChild; c != nil; c = c.NextSibling {
-		if c.Type == html.ElementNode && isHidden(c) {
+		if c.Type == html.ElementNode && cv.isHidden(c) {
 			continue
 		}
 
@@ -789,7 +793,7 @@ func (cv *conversion) wrapSpans(o *output, n *html.Node) (*html.Node, bool) {
 			return c.PrevSibling, false
 		}
 
-		if c.Type == html.ElementNode && isHidden(c) {
+		if c.Type == html.ElementNode && cv.isHidden(c) {
 			continue
 		}
 
@@ -873,7 +877,11 @@ func isPreheaderMark(r rune) bool {
 
 // isHidden reports whether an element is kept out of the rendered message.
 // Preheader text meant only for the inbox preview is the usual case.
-func isHidden(n *html.Node) bool {
+func (cv *conversion) isHidden(n *html.Node) bool {
+	if cv.opts.hiddenContent {
+		return false
+	}
+
 	for _, a := range n.Attr {
 		switch a.Key {
 		case "hidden":
@@ -892,7 +900,11 @@ func isHidden(n *html.Node) bool {
 	return false
 }
 
+// font-size:0 is left out: it is inherited and descendants reset it, as in the
+// inline-block gap fix that wraps whole layouts
 func hiddenByStyle(style string) bool {
+	var zeroHeight, overflowHidden bool
+
 	for declaration := range strings.SplitSeq(style, ";") {
 		property, value, ok := strings.Cut(declaration, ":")
 		if !ok {
@@ -911,14 +923,18 @@ func hiddenByStyle(style string) bool {
 			if value == "hidden" || value == "collapse" {
 				return true
 			}
-		case "opacity", "font-size", "max-height":
+		case "opacity":
 			if isZeroValue(value) {
 				return true
 			}
+		case "max-height":
+			zeroHeight = isZeroValue(value)
+		case "overflow", "overflow-y":
+			overflowHidden = value == "hidden"
 		}
 	}
 
-	return false
+	return zeroHeight && overflowHidden
 }
 
 // isZeroValue reports whether a css number or length is zero, with or without a unit,