hugolib: Fix regression of .Truncated evaluation in manual summaries

This fixes the behavior of .Truncated that was introduced with commit
bef496b97e which was later broken.  The
desired behavior is that .Truncated would evaluate to false when there
was nothing after the user defined summary marker.

This also adds a simple unit test to ensure that this feature isn't
broken again.  The check for content after the user defined summary
marker is done on the raw content instead of the working copy because
some of the markup renderers add elements after the marker, making it
difficult to determine if there is actually any content.

The behavior (evaluating to false when there is no content, just
summary) is also now documented.

hugolib/page_test.go

@@ -164,6 +164,14 @@ title: Simple
 Summary Same Line<!--more-->
 
 Some more text
+`
+
+	simplePageWithSummaryDelimiterOnlySummary = `---
+title: Simple
+---
+Summary text
+
+<!--more-->
 `
 
 	simplePageWithAllCJKRunes = `---
@@ -665,46 +673,42 @@ func TestCreateNewPage(t *testing.T) {
 func TestSplitSummaryAndContent(t *testing.T) {
 	t.Parallel()
 	for i, this := range []struct {
-		markup                        string
-		content                       string
-		expectedSummary               string
-		expectedContent               string
-		expectedContentWithoutSummary string
+		markup          string
+		content         string
+		expectedSummary string
+		expectedContent string
 	}{
 		{"markdown", `<p>Summary Same LineHUGOMORE42</p>
 
-<p>Some more text</p>`, "<p>Summary Same Line</p>", "<p>Summary Same Line</p>\n\n<p>Some more text</p>", "<p>Some more text</p>"},
+<p>Some more text</p>`, "<p>Summary Same Line</p>", "<p>Summary Same Line</p>\n\n<p>Some more text</p>"},
 		{"asciidoc", `<div class="paragraph"><p>sn</p></div><div class="paragraph"><p>HUGOMORE42Some more text</p></div>`,
 			"<div class=\"paragraph\"><p>sn</p></div>",
-			"<div class=\"paragraph\"><p>sn</p></div><div class=\"paragraph\"><p>Some more text</p></div>",
-			"<div class=\"paragraph\"><p>Some more text</p></div>"},
+			"<div class=\"paragraph\"><p>sn</p></div><div class=\"paragraph\"><p>Some more text</p></div>"},
 		{"rst",
 			"<div class=\"document\"><p>Summary Next Line</p><p>HUGOMORE42Some more text</p></div>",
 			"<div class=\"document\"><p>Summary Next Line</p></div>",
-			"<div class=\"document\"><p>Summary Next Line</p><p>Some more text</p></div>",
-			"<div class=\"document\"><p>Some more text</p></div>"},
-		{"markdown", "<p>a</p><p>b</p><p>HUGOMORE42c</p>", "<p>a</p><p>b</p>", "<p>a</p><p>b</p><p>c</p>", "<p>c</p>"},
-		{"markdown", "<p>a</p><p>b</p><p>cHUGOMORE42</p>", "<p>a</p><p>b</p><p>c</p>", "<p>a</p><p>b</p><p>c</p>", ""},
-		{"markdown", "<p>a</p><p>bHUGOMORE42</p><p>c</p>", "<p>a</p><p>b</p>", "<p>a</p><p>b</p><p>c</p>", "<p>c</p>"},
-		{"markdown", "<p>aHUGOMORE42</p><p>b</p><p>c</p>", "<p>a</p>", "<p>a</p><p>b</p><p>c</p>", "<p>b</p><p>c</p>"},
-		{"markdown", "  HUGOMORE42 ", "", "", ""},
-		{"markdown", "HUGOMORE42", "", "", ""},
-		{"markdown", "<p>HUGOMORE42", "<p>", "<p>", ""},
-		{"markdown", "HUGOMORE42<p>", "", "<p>", "<p>"},
-		{"markdown", "\n\n<p>HUGOMORE42</p>\n", "<p></p>", "<p></p>", ""},
+			"<div class=\"document\"><p>Summary Next Line</p><p>Some more text</p></div>"},
+		{"markdown", "<p>a</p><p>b</p><p>HUGOMORE42c</p>", "<p>a</p><p>b</p>", "<p>a</p><p>b</p><p>c</p>"},
+		{"markdown", "<p>a</p><p>b</p><p>cHUGOMORE42</p>", "<p>a</p><p>b</p><p>c</p>", "<p>a</p><p>b</p><p>c</p>"},
+		{"markdown", "<p>a</p><p>bHUGOMORE42</p><p>c</p>", "<p>a</p><p>b</p>", "<p>a</p><p>b</p><p>c</p>"},
+		{"markdown", "<p>aHUGOMORE42</p><p>b</p><p>c</p>", "<p>a</p>", "<p>a</p><p>b</p><p>c</p>"},
+		{"markdown", "  HUGOMORE42 ", "", ""},
+		{"markdown", "HUGOMORE42", "", ""},
+		{"markdown", "<p>HUGOMORE42", "<p>", "<p>"},
+		{"markdown", "HUGOMORE42<p>", "", "<p>"},
+		{"markdown", "\n\n<p>HUGOMORE42</p>\n", "<p></p>", "<p></p>"},
 		// Issue #2586
 		// Note: Hugo will not split mid-sentence but will look for the closest
 		// paragraph end marker. This may be a change from Hugo 0.16, but it makes sense.
 		{"markdown", `<p>this is an example HUGOMORE42of the issue.</p>`,
 			"<p>this is an example of the issue.</p>",
-			"<p>this is an example of the issue.</p>", ""},
+			"<p>this is an example of the issue.</p>"},
 		// Issue: #2538
 		{"markdown", fmt.Sprintf(` <p class="lead">%s</p>HUGOMORE42<p>%s</p>
 `,
 			strings.Repeat("A", 10), strings.Repeat("B", 31)),
 			fmt.Sprintf(`<p class="lead">%s</p>`, strings.Repeat("A", 10)),
 			fmt.Sprintf(`<p class="lead">%s</p><p>%s</p>`, strings.Repeat("A", 10), strings.Repeat("B", 31)),
-			fmt.Sprintf(`<p>%s</p>`, strings.Repeat("B", 31)),
 		},
 	} {
 
@@ -714,7 +718,6 @@ func TestSplitSummaryAndContent(t *testing.T) {
 		require.NotNil(t, sc, fmt.Sprintf("[%d] Nil %s", i, this.markup))
 		require.Equal(t, this.expectedSummary, string(sc.summary), fmt.Sprintf("[%d] Summary markup %s", i, this.markup))
 		require.Equal(t, this.expectedContent, string(sc.content), fmt.Sprintf("[%d] Content markup %s", i, this.markup))
-		require.Equal(t, this.expectedContentWithoutSummary, string(sc.contentWithoutSummary), fmt.Sprintf("[%d] Content without summary, markup %s", i, this.markup))
 	}
 }
 
@@ -850,6 +853,16 @@ func TestPageWithMoreTag(t *testing.T) {
 	testAllMarkdownEnginesForPages(t, assertFunc, nil, simplePageWithSummaryDelimiterSameLine)
 }
 
+func TestPageWithMoreTagOnlySummary(t *testing.T) {
+
+	assertFunc := func(t *testing.T, ext string, pages Pages) {
+		p := pages[0]
+		checkTruncation(t, p, false, "page with summary delimiter at end")
+	}
+
+	testAllMarkdownEnginesForPages(t, assertFunc, nil, simplePageWithSummaryDelimiterOnlySummary)
+}
+
 func TestPageWithDate(t *testing.T) {
 	t.Parallel()
 	cfg, fs := newTestCfg()