Ensure page translation CPs are initialized

PR gohugoio#9342 introduced a regression in which calling .Translations in a
template and calling RenderString on a translated Page caused a nil
pointer dereference. The issue was that some Pages returned from
.Translations had a nil cp field at the time the calling template was
being executed.

While PR gohugoio#9342 had attempted to ensure that all ContentProviders were
initialized for translations at build time, it only performed the
initialization for receivers of ContentProvider methods such as
.Summary. However, the ContentProvider's *pageState.pageOutput.cp would
remain uninitialized, causing the nil pointer dereference.

This change edits the .Translations and .AllTranslations methods to
ensure that all of a page's translations have an initialized
content provider in time for a template to be executed.

Since LazyContentProvider is no longer needed with this approach, this
change also reverts the following commits:

- cdcd15b
- 25d645f

Fixes gohugoio#9383

hugolib/page.go

@@ -369,12 +369,50 @@ func (p *pageState) TranslationKey() string {
 // AllTranslations returns all translations, including the current Page.
 func (p *pageState) AllTranslations() page.Pages {
 	p.s.h.init.translations.Do()
+
+	// Hugo attempts to reuse content providers while preparing each page for
+	// rendering. This approach means that sometimes, content providers for
+	// translations are not initialized. If needed, initialize them here.
+	for _, tr := range p.allTranslations {
+		tp, ok := tr.(*pageState)
+		if !ok {
+			continue
+		}
+		if tp.pageOutput.cp == nil {
+			cp, err := newPageContentOutput(tp, tp.pageOutput)
+			if err != nil {
+				// This will be caught by texttemplate.safeCall
+				panic(fmt.Errorf("error rendering page translation: %w", err))
+			}
+			tp.initContentProvider(cp)
+		}
+	}
+
 	return p.allTranslations
 }
 
 // Translations returns the translations excluding the current Page.
 func (p *pageState) Translations() page.Pages {
 	p.s.h.init.translations.Do()
+
+	// Hugo attempts to reuse content providers while preparing each page for
+	// rendering. This approach means that sometimes, content providers for
+	// translations are not initialized. If needed, initialize them here.
+	for _, tr := range p.translations {
+		tp, ok := tr.(*pageState)
+		if !ok {
+			continue
+		}
+		if tp.pageOutput.cp == nil {
+			cp, err := newPageContentOutput(tp, tp.pageOutput)
+			if err != nil {
+				// This will be caught by texttemplate.safeCall
+				panic(fmt.Errorf("error rendering page translation: %w", err))
+			}
+			tp.initContentProvider(cp)
+		}
+	}
+
 	return p.translations
 }
 
@@ -971,24 +1009,6 @@ func (p *pageState) shiftToOutputFormat(isRenderingSite bool, idx int) error {
 			}
 		}
 		p.pageOutput.initContentProvider(cp)
-	} else {
-		// We attempt to assign pageContentOutputs while preparing each site
-		// for rendering and before rendering each site. This lets us share
-		// content between page outputs to conserve resources. But if a template
-		// unexpectedly calls a method of a ContentProvider that is not yet
-		// initialized, we assign a LazyContentProvider that performs the
-		// initialization just in time.
-		if lcp, ok := (p.pageOutput.ContentProvider.(*page.LazyContentProvider)); ok {
-			lcp.Reset()
-		} else {
-			p.pageOutput.ContentProvider = page.NewLazyContentProvider(func() (page.ContentProvider, error) {
-				cp, err := newPageContentOutput(p, p.pageOutput)
-				if err != nil {
-					return nil, err
-				}
-				return cp, nil
-			})
-		}
 	}
 
 	return nil

hugolib/page_test.go

@@ -768,6 +768,69 @@ Here is the last report for commits in the year 2016. It covers hrev50718-hrev50
 `)
 }
 
+// Issue 9383
+func TestRenderStringForRegularPageTranslations(t *testing.T) {
+	c := qt.New(t)
+	b := newTestSitesBuilder(t)
+	b.WithLogger(loggers.NewBasicLoggerForWriter(jwalterweatherman.LevelDebug, os.Stderr))
+
+	b.WithConfigFile("toml",
+		`baseurl = "https://example.org/"
+title = "My Site"
+
+defaultContentLanguage = "ru"
+defaultContentLanguageInSubdir = true
+
+[languages.ru]
+contentDir = 'content/ru'
+weight = 1
+
+[languages.en]
+weight = 2
+contentDir = 'content/en'
+
+[outputs]
+home = ["HTML", "JSON"]`)
+
+	b.WithTemplates("index.html", `
+{{- range .Site.Home.Translations -}}
+	<p>{{- .RenderString "foo" -}}</p>
+{{- end -}}
+{{- range .Site.Home.AllTranslations -}}
+	<p>{{- .RenderString "bar" -}}</p>
+{{- end -}}
+`, "_default/single.html",
+		`{{ .Content }}`,
+		"index.json",
+		`{"Title": "My Site"}`,
+	)
+
+	b.WithContent(
+		"ru/a.md",
+		"",
+		"en/a.md",
+		"",
+	)
+
+	err := b.BuildE(BuildCfg{})
+	c.Assert(err, qt.Equals, nil)
+
+	b.AssertFileContent("public/ru/index.html", `
+<p>foo</p>
+<p>foo</p>
+<p>bar</p>
+<p>bar</p>
+`)
+
+	b.AssertFileContent("public/en/index.html", `
+<p>foo</p>
+<p>foo</p>
+<p>bar</p>
+<p>bar</p>
+`)
+
+}
+
 // Issue 8919
 func TestContentProviderWithCustomOutputFormat(t *testing.T) {
 	b := newTestSitesBuilder(t)