Read .po nplurals from the parsed header, not a raw-file scan

`declared_nplurals` re-read the `.po` line by line and returned the first
`nplurals=` it found anywhere, so a stray occurrence before the real
`Plural-Forms` header (a comment, a translated string) would be read as the
form count and make `guard_po_plural_count!` abort with a spurious error.
Real GlotPress exports were unaffected, but the scan was needlessly fragile
— and redundant, since the `.po` is already parsed by then.

Read `nplurals` from the parsed header entry (`po[nil, '']`), whose `msgstr`
holds only the header fields, so no token elsewhere in the file can be
mistaken for it. Drops the extra file read too.

Author: jkmassel

lib/fastlane/plugin/wpmreleasetoolkit/helper/ios/ios_stringsdict_helper.rb

@@ -146,7 +146,7 @@ def self.generate_stringsdict_from_po(po_path:, template_path:, locale:, output_
           # has. If the .po's own declared count disagrees with our mapping,
           # GlotPress has changed its plural rule for this locale — fail loud
           # (the signal to regenerate PluralRules) rather than silently mis-map.
-          guard_po_plural_count!(po_path: po_path, locale: locale, categories: categories)
+          guard_po_plural_count!(parsed_po: po, locale: locale, categories: categories)
 
           missing = []
           result = {}
@@ -336,21 +336,22 @@ def self.parse_po(path)
 
         # The `nplurals` value declared in the `.po`'s `Plural-Forms` header
         # (GlotPress's authoritative form count for the locale), or `nil` if the
-        # header is absent. Read straight from the file so it doesn't depend on
-        # how the parser exposes the header entry.
-        def self.declared_nplurals(po_path)
-          File.foreach(po_path) do |line|
-            m = line.match(/nplurals\s*=\s*(\d+)/)
-            return Integer(m[1]) if m
-          end
-          nil
+        # header is absent. Read from the parsed header entry, whose `msgstr`
+        # holds only the header fields — so a stray `nplurals=` token elsewhere
+        # in the file (a comment, a translated string) can't be mistaken for it.
+        def self.declared_nplurals(parsed_po)
+          header = parsed_po[nil, '']
+          return nil if header.nil? || header.msgstr.nil?
+
+          match = header.msgstr.match(/nplurals\s*=\s*(\d+)/)
+          match && Integer(match[1])
         end
 
         # Fail loud if the `.po`'s declared plural-form count doesn't match the
         # number of CLDR categories we expect for the locale — i.e. GlotPress's
         # plural rule has drifted from {PluralRules}.
-        def self.guard_po_plural_count!(po_path:, locale:, categories:)
-          declared = declared_nplurals(po_path)
+        def self.guard_po_plural_count!(parsed_po:, locale:, categories:)
+          declared = declared_nplurals(parsed_po)
           return if declared.nil? || declared == categories.size
 
           UI.user_error!("Locale '#{locale}': the .po declares nplurals=#{declared}, but the expected plural mapping has " \

spec/ios_stringsdict_helper_spec.rb

@@ -353,5 +353,26 @@ def convert_po_to_stringsdict(po_content, template:, locale:)
         convert_po_to_stringsdict(simple_po(forms: %w[a b], nplurals: 2), template: simple, locale: 'ru')
       end.to raise_error(FastlaneCore::Interface::FastlaneError, /declares nplurals=2.*3 categor/m)
     end
+
+    it 'reads nplurals from the header, not a stray `nplurals=` elsewhere in the .po' do
+      po = <<~PO
+        # A misleading comment that mentions nplurals=4 must not be picked up.
+        msgid ""
+        msgstr ""
+        "Plural-Forms: nplurals=3; plural=(n != 1);\\n"
+
+        msgctxt "%d items"
+        msgid "%d item"
+        msgid_plural "%d items"
+        msgstr[0] "ru-one"
+        msgstr[1] "ru-few"
+        msgstr[2] "ru-many"
+      PO
+      data, missing = convert_po_to_stringsdict(po, template: simple, locale: 'ru')
+      expect(missing).to be_empty
+      expect(data['%d items']['count'].slice('one', 'few', 'many')).to eq(
+        'one' => 'ru-one', 'few' => 'ru-few', 'many' => 'ru-many'
+      )
+    end
   end
 end