feat: links settings and outbound rules in resolve

- migration 202610280003: settings links_new_tab (default on),
  nofollow_domains and sponsored_domains; robots llms_enabled and
  llms_intro (used by the llms.txt commit)
- SEO settings Links tab: the new-tab switch and the two domain lists,
  one domain per line, lowercased, refused with settings.domain_invalid
  naming the line; writable through seo_update_settings
- the resolve answer of an ok page carries outbound {new_tab,
  nofollow_domains, sponsored_domains}; no existing key changes

models/settings.go

@@ -3,8 +3,10 @@ package models
 import (
 	"fmt"
 	"regexp"
+	"strconv"
 	"strings"
 	"time"
+	"unicode"
 
 	"git.golem15.com/golem15/summercms/modules/lagoon"
 )
@@ -37,6 +39,7 @@ const (
 	errVerifyFilenameInvalid = "golem15.seo::lang.settings.verify_filename_invalid"
 	errVerifyFilenameTaken   = "golem15.seo::lang.settings.verify_filename_taken"
 	errTemplateUnknown       = "golem15.seo::lang.settings.template_unknown"
+	errDomainInvalid         = "golem15.seo::lang.settings.domain_invalid"
 )
 
 // QueryParam is one row of the D-07 query-parameter list: a name (a
@@ -95,6 +98,13 @@ type Settings struct {
 	VerifyOther        lagoon.Jsonable[[]VerifyMeta] `gorm:"column:verify_other"`
 	VerifyFiles        lagoon.Jsonable[[]VerifyFile] `gorm:"column:verify_files"`
 	CSVDelimiter       string                        `gorm:"column:csv_delimiter"`
+	// LinksNewTab opens links to other sites in a new tab (Links tab, on
+	// by default); NofollowDomains and SponsoredDomains list the domains
+	// whose links always get nofollow or sponsored, one per line,
+	// subdomains included (D-83).
+	LinksNewTab      bool   `gorm:"column:links_new_tab"`
+	NofollowDomains  string `gorm:"column:nofollow_domains"`
+	SponsoredDomains string `gorm:"column:sponsored_domains"`
 	// RoutesReportedAt is the time of the newest route report (D-33),
 	// written by the report only.
 	RoutesReportedAt *time.Time `gorm:"column:routes_reported_at"`
@@ -114,7 +124,8 @@ func (Settings) Fillable() []string {
 		"default_description", "default_og_image", "query_params",
 		"noindex_paths", "search_paths", "url_host", "url_slash",
 		"url_lowercase", "verify_google", "verify_bing", "verify_yandex",
-		"verify_other", "verify_files",
+		"verify_other", "verify_files", "links_new_tab", "nofollow_domains",
+		"sponsored_domains",
 	}
 }
 
@@ -130,6 +141,7 @@ func DefaultSettings() Settings {
 		QueryParams:   lagoon.Jsonable[[]QueryParam]{Data: DefaultQueryParams(), Valid: true},
 		URLHost:       HostKeep,
 		URLSlash:      SlashKeep,
+		LinksNewTab:   true,
 	}
 }
 
@@ -206,9 +218,82 @@ func (s Settings) Problems() map[string][]Problem {
 		}
 		seen[strings.ToLower(name)] = true
 	}
+	for field, list := range map[string]string{"nofollow_domains": s.NofollowDomains, "sponsored_domains": s.SponsoredDomains} {
+		if p := DomainProblems(list); p != nil {
+			out[field] = p
+		}
+	}
 	return out
 }
 
+// domainLabel is one label of a host name: letters (any script, written
+// in lowercase), digits and inner hyphens, at most 63 bytes.
+func domainLabel(label string) bool {
+	if label == "" || len(label) > 63 || strings.HasPrefix(label, "-") || strings.HasSuffix(label, "-") {
+		return false
+	}
+	for _, r := range label {
+		if r != '-' && !unicode.IsDigit(r) && !(unicode.IsLetter(r) && !unicode.IsUpper(r)) {
+			return false
+		}
+	}
+	return true
+}
+
+// ValidDomain reports whether d is a host name with at least two labels,
+// without a scheme, port, path or trailing dot.
+func ValidDomain(d string) bool {
+	if d == "" || len(d) > 253 {
+		return false
+	}
+	labels := strings.Split(d, ".")
+	if len(labels) < 2 {
+		return false
+	}
+	for _, l := range labels {
+		if !domainLabel(l) {
+			return false
+		}
+	}
+	return true
+}
+
+// DomainLines splits a domain list into its trimmed, lowercased,
+// non-empty lines, in order and each once.
+func DomainLines(list string) []string {
+	out := []string{}
+	seen := map[string]bool{}
+	for _, line := range strings.Split(strings.ReplaceAll(list, "\r\n", "\n"), "\n") {
+		d := strings.ToLower(strings.TrimSpace(line))
+		if d == "" || seen[d] {
+			continue
+		}
+		seen[d] = true
+		out = append(out, d)
+	}
+	return out
+}
+
+// NormalizeDomains rewrites a domain list as DomainLines, one per line.
+func NormalizeDomains(list string) string {
+	return strings.Join(DomainLines(list), "\n")
+}
+
+// DomainProblems refuses the first line of list that is not a domain
+// (settings.domain_invalid with its line number and text).
+func DomainProblems(list string) []Problem {
+	n := 0
+	for _, line := range strings.Split(strings.ReplaceAll(list, "\r\n", "\n"), "\n") {
+		n++
+		d := strings.ToLower(strings.TrimSpace(line))
+		if d == "" || ValidDomain(d) {
+			continue
+		}
+		return []Problem{{Key: errDomainInvalid, Params: map[string]string{"line": strconv.Itoa(n), "value": strings.TrimSpace(line)}}}
+	}
+	return nil
+}
+
 func init() {
 	Register(Settings{})
 }

models/settings/fields.yaml

@@ -3,8 +3,8 @@
 # ===================================
 #
 # SEO settings (UI-SPEC C11): General, one tab per content type (added by
-# the plugin's form extension after General), Indexing, Addresses and
-# Verification.
+# the plugin's form extension after General), Indexing, Addresses, Links
+# (UI-SPEC C20) and Verification.
 
 fields:
     _staging:
@@ -139,6 +139,30 @@ fields:
         default: false
         tab: golem15.seo::lang.settings.tab_urls
 
+    links_new_tab:
+        label: golem15.seo::lang.settings.links_new_tab
+        comment: golem15.seo::lang.settings.links_new_tab_comment
+        type: switch
+        span: right
+        default: true
+        tab: golem15.seo::lang.settings.tab_links
+
+    nofollow_domains:
+        label: golem15.seo::lang.settings.nofollow_domains
+        comment: golem15.seo::lang.settings.domains_comment
+        type: textarea
+        size: small
+        span: left
+        tab: golem15.seo::lang.settings.tab_links
+
+    sponsored_domains:
+        label: golem15.seo::lang.settings.sponsored_domains
+        comment: golem15.seo::lang.settings.domains_comment
+        type: textarea
+        size: small
+        span: right
+        tab: golem15.seo::lang.settings.tab_links
+
     verify_google:
         label: golem15.seo::lang.settings.verify_google
         comment: golem15.seo::lang.settings.verify_code_comment