Make WARN the new default log log level

This commit also pulls down the log level for a set of WARN statements to INFO. There should be no ERRORs or WARNINGs in a regular Hugo build. That is the story about the Boy Who Cried Wolf.

Since the WARN log is now more visible, this commit also improves on some of them, most notable the "layout not found", which now would look something like this:

```bash
WARN 2018/11/02 09:02:18 Found no layout for "home", language "en", output format "CSS": create a template below /layouts with one of these filenames: index.en.css.css, home.en.css.css, list.en.css.css, index.css.css, home.css.css, list.css.css, index.en.css, home.en.css, list.en.css, index.css, home.css, list.css, _default/index.en.css.css, _default/home.en.css.css, _default/list.en.css.css, _default/index.css.css, _default/home.css.css, _default/list.css.css, _default/index.en.css, _default/home.en.css, _default/list.en.css, _default/index.css, _default/home.css, _default/list.css
```

Fixes #5203

8 files changed, 44 insertions, 21 deletions

diff --git a/commands/hugo.go b/commands/hugo.go
index 7d2fa9803..175c6dc99 100644
--- a/commands/hugo.go
+++ b/commands/hugo.go
@@ -131,7 +131,7 @@ func (c *commandeer) createLogger(cfg config.Provider, running bool) (*loggers.L
 		logThreshold    = jww.LevelWarn
 		logFile         = cfg.GetString("logFile")
 		outHandle       = os.Stdout
-		stdoutThreshold = jww.LevelError
+		stdoutThreshold = jww.LevelWarn
 	)
 
 	if c.h.verboseLog || c.h.logging || (c.h.logFile != "") {
@@ -294,7 +294,7 @@ func (c *commandeer) fullBuild() error {
 			if !os.IsNotExist(err) {
 				return errors.Wrap(err, "Error copying static files")
 			}
-			c.logger.WARN.Println("No Static directory found")
+			c.logger.INFO.Println("No Static directory found")
 		}
 		langCount = cnt
 		langCount = cnt
@@ -405,7 +405,7 @@ func (c *commandeer) doWithPublishDirs(f func(sourceFs *filesystems.SourceFilesy
 	staticFilesystems := c.hugo.BaseFs.SourceFilesystems.Static
 
 	if len(staticFilesystems) == 0 {
-		c.logger.WARN.Println("No static directories found to sync")
+		c.logger.INFO.Println("No static directories found to sync")
 		return langCount, nil
 	}
 
diff --git a/hugolib/alias.go b/hugolib/alias.go
index bcf8f1963..c44f32dbb 100644
--- a/hugolib/alias.go
+++ b/hugolib/alias.go
@@ -174,7 +174,7 @@ func (a aliasHandler) targetPathAlias(src string) (string, error) {
 			return "", fmt.Errorf("Cannot create \"%s\": Windows filename restriction", originalAlias)
 		}
 		for _, m := range msgs {
-			a.log.WARN.Println(m)
+			a.log.INFO.Println(m)
 		}
 	}
 
diff --git a/hugolib/page.go b/hugolib/page.go
index d91082b3b..070df133b 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -326,7 +326,7 @@ func (p *Page) initContent() {
 
 		select {
 		case <-ctx.Done():
-			p.s.Log.WARN.Printf("WARNING: Timed out creating content for page %q (.Content will be empty). This is most likely a circular shortcode content loop that should be fixed. If this is just a shortcode calling a slow remote service, try to set \"timeout=20000\" (or higher, value is in milliseconds) in config.toml.\n", p.pathOrTitle())
+			p.s.Log.WARN.Printf("Timed out creating content for page %q (.Content will be empty). This is most likely a circular shortcode content loop that should be fixed. If this is just a shortcode calling a slow remote service, try to set \"timeout=30000\" (or higher, value is in milliseconds) in config.toml.\n", p.pathOrTitle())
 		case err := <-c:
 			if err != nil {
 				p.s.SendError(err)
@@ -1456,7 +1456,7 @@ func (p *Page) updateMetaData(frontmatter map[string]interface{}) error {
 
 	if draft != nil && published != nil {
 		p.Draft = *draft
-		p.s.Log.WARN.Printf("page %q has both draft and published settings in its frontmatter. Using draft.", p.File.Path())
+		p.s.Log.WARN.Printf("page %q has both draft and published settings in its frontmatter. Using draft.", p.Filename())
 	} else if draft != nil {
 		p.Draft = *draft
 	} else if published != nil {
@@ -1973,8 +1973,6 @@ func (p *Page) initLanguage() {
 		language := ml.Language(p.lang)
 
 		if language == nil {
-			// It can be a file named stefano.chiodino.md.
-			p.s.Log.WARN.Printf("Page language (if it is that) not found in multilang setup: %s.", p.lang)
 			language = ml.DefaultLang
 		}
 
diff --git a/hugolib/page_content.go b/hugolib/page_content.go
index dc043f824..75124a1df 100644
--- a/hugolib/page_content.go
+++ b/hugolib/page_content.go
@@ -188,7 +188,7 @@ func (p *Page) parse(reader io.Reader) error {
 		if gi != nil {
 			p.GitInfo = gi
 		} else if enabled {
-			p.s.Log.WARN.Printf("Failed to find GitInfo for page %q", p.Path())
+			p.s.Log.INFO.Printf("Failed to find GitInfo for page %q", p.Path())
 		}
 	}
 
diff --git a/hugolib/pagebundler_capture.go b/hugolib/pagebundler_capture.go
index c152262cc..446d3b0c7 100644
--- a/hugolib/pagebundler_capture.go
+++ b/hugolib/pagebundler_capture.go
@@ -679,7 +679,7 @@ func (c *capturer) isSeen(dirname string) bool {
 	seen := c.seen[dirname]
 	c.seen[dirname] = true
 	if seen {
-		c.logger.WARN.Printf("Content dir %q already processed; skipped to avoid infinite recursion.", dirname)
+		c.logger.INFO.Printf("Content dir %q already processed; skipped to avoid infinite recursion.", dirname)
 		return true
 
 	}
diff --git a/hugolib/site.go b/hugolib/site.go
index e58dd39b2..761d4a6bd 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -956,7 +956,7 @@ func (s *Site) handleDataFile(r source.ReadableFile) error {
 			higherPrecedentMap := higherPrecedentData.(map[string]interface{})
 			for key, value := range data.(map[string]interface{}) {
 				if _, exists := higherPrecedentMap[key]; exists {
-					s.Log.WARN.Printf("Data for key '%s' in path '%s' is overridden higher precedence data already in the data tree", key, r.Path())
+					s.Log.WARN.Printf("Data for key '%s' in path '%s' is overridden by higher precedence data already in the data tree", key, r.Path())
 				} else {
 					higherPrecedentMap[key] = value
 				}
@@ -1759,24 +1759,49 @@ func (s *Site) renderAndWritePage(statCounter *uint64, name string, targetPath s
 	return s.publisher.Publish(pd)
 }
 
+var infoOnMissingLayout = map[string]bool{
+	// The 404 layout is very much optional in Hugo, but we do look for it.
+	"404": true,
+}
+
 func (s *Site) renderForLayouts(name string, d interface{}, w io.Writer, layouts ...string) (err error) {
 	var templ tpl.Template
 
 	templ = s.findFirstTemplate(layouts...)
 	if templ == nil {
-		s.Log.WARN.Printf("[%s] Unable to locate layout for %q: %s\n", s.Language.Lang, name, layouts)
+		log := s.Log.WARN
+		if infoOnMissingLayout[name] {
+			log = s.Log.INFO
+		}
+
+		if p, ok := d.(*PageOutput); ok {
+			log.Printf("Found no layout for %q, language %q, output format %q: create a template below /layouts with one of these filenames: %s\n", name, s.Language.Lang, p.outputFormat.Name, layoutsLogFormat(layouts))
+		} else {
+			log.Printf("Found no layout for %q, language %q: create a template below /layouts with one of these filenames: %s\n", name, s.Language.Lang, layoutsLogFormat(layouts))
+		}
 		return nil
 	}
 
 	if err = templ.Execute(w, d); err != nil {
-		if p, ok := d.(*PageOutput); ok {
-			return p.errorf(err, "render of %q failed", name)
-		}
 		return _errors.Wrapf(err, "render of %q failed", name)
 	}
 	return
 }
 
+func layoutsLogFormat(layouts []string) string {
+	var filtered []string
+	for _, l := range layouts {
+		// This is  a technical prefix of no interest to the user.
+		lt := strings.TrimPrefix(l, "_text/")
+		// We have this in the lookup path for historical reasons.
+		lt = strings.TrimPrefix(lt, "page/")
+		filtered = append(filtered, lt)
+	}
+
+	filtered = helpers.UniqueStrings(filtered)
+	return strings.Join(filtered, ", ")
+}
+
 func (s *Site) findFirstTemplate(layouts ...string) tpl.Template {
 	for _, layout := range layouts {
 		if templ, found := s.Tmpl.Lookup(layout); found {
diff --git a/i18n/i18n.go b/i18n/i18n.go
index d395bbf62..25f2d300e 100644
--- a/i18n/i18n.go
+++ b/i18n/i18n.go
@@ -45,11 +45,11 @@ func (t Translator) Func(lang string) bundle.TranslateFunc {
 	if f, ok := t.translateFuncs[lang]; ok {
 		return f
 	}
-	t.logger.WARN.Printf("Translation func for language %v not found, use default.", lang)
+	t.logger.INFO.Printf("Translation func for language %v not found, use default.", lang)
 	if f, ok := t.translateFuncs[t.cfg.GetString("defaultContentLanguage")]; ok {
 		return f
 	}
-	t.logger.WARN.Println("i18n not initialized, check that you have language file (in i18n) that matches the site language or the default language.")
+	t.logger.INFO.Println("i18n not initialized; if you need string translations, check that you have a bundle in /i18n that matches the site language or the default language.")
 	return func(translationID string, args ...interface{}) string {
 		return ""
 	}
@@ -61,7 +61,7 @@ func (t Translator) initFuncs(bndl *bundle.Bundle) {
 
 	defaultT, err := bndl.Tfunc(defaultContentLanguage)
 	if err != nil {
-		t.logger.WARN.Printf("No translation bundle found for default language %q", defaultContentLanguage)
+		t.logger.INFO.Printf("No translation bundle found for default language %q", defaultContentLanguage)
 	}
 
 	enableMissingTranslationPlaceholders := t.cfg.GetBool("enableMissingTranslationPlaceholders")
diff --git a/tpl/data/data.go b/tpl/data/data.go
index 8b3eb8292..cecce4b45 100644
--- a/tpl/data/data.go
+++ b/tpl/data/data.go
@@ -50,7 +50,7 @@ func (ns *Namespace) GetCSV(sep string, urlParts ...string) (d [][]string, err e
 	url := strings.Join(urlParts, "")
 
 	var clearCacheSleep = func(i int, u string) {
-		ns.deps.Log.WARN.Printf("Retry #%d for %s and sleeping for %s", i, url, resSleep)
+		ns.deps.Log.INFO.Printf("Retry #%d for %s and sleeping for %s", i, url, resSleep)
 		time.Sleep(resSleep)
 		deleteCache(url, ns.deps.Fs.Source, ns.deps.Cfg)
 	}
@@ -109,8 +109,8 @@ func (ns *Namespace) GetJSON(urlParts ...string) (v interface{}, err error) {
 		}
 		err = json.Unmarshal(c, &v)
 		if err != nil {
-			ns.deps.Log.WARN.Printf("Cannot read JSON from resource %s: %s", url, err)
-			ns.deps.Log.WARN.Printf("Retry #%d for %s and sleeping for %s", i, url, resSleep)
+			ns.deps.Log.INFO.Printf("Cannot read JSON from resource %s: %s", url, err)
+			ns.deps.Log.INFO.Printf("Retry #%d for %s and sleeping for %s", i, url, resSleep)
 			time.Sleep(resSleep)
 			deleteCache(url, ns.deps.Fs.Source, ns.deps.Cfg)
 			continue