Tolerate duplicate iconv aliases on macOS

src/iconv.c

@@ -272,9 +272,11 @@ module_iconv (RECODE_OUTER outer)
 	  RECODE_ALIAS alias
 	    = recode_find_alias (outer, *cursor, ALIAS_FIND_AS_CHARSET);
 
-	  /* If there is a charset contradiction, call recode_declare_alias
-	     nevertheless, as the error processing will occur there.  */
-	  if (!alias || alias->symbol->name != charset_name)
+	  /* Only declare aliases not already known.  Some iconv
+	     implementations (notably macOS libiconv) list the same alias
+	     under more than one charset group, e.g. WINDOWS-874 under both
+	     CP1162 and CP874; keep the first binding rather than aborting.  */
+	  if (!alias)
 	    if (!recode_declare_alias (outer, *cursor, charset_name))
 	      return false;
 	}

tables.py

@@ -468,6 +468,7 @@ def digest(self):
         libc = None
         import os
         names = []
+        seen = set()
         for line in os.popen('iconv -l'):
             if libc is None:
                 libc = len(line.split('/')) == 3
@@ -484,7 +485,19 @@ def digest(self):
                     if alias in canonical:
                         alias = canonical[alias]
                     aliases.append(alias)
-                self.data.append((aliases[0], aliases[1:]))
+                # Prefer the first charset group for each alias name.  Some
+                # iconv implementations (macOS libiconv) repeat names across
+                # groups — e.g. WINDOWS-874 under both CP1162 and CP874 —
+                # which would otherwise make module_iconv abort.
+                filtered = []
+                for alias in aliases:
+                    key = alias.upper()
+                    if key in seen:
+                        continue
+                    seen.add(key)
+                    filtered.append(alias)
+                if filtered:
+                    self.data.append((filtered[0], filtered[1:]))
 
     def complete(self, french):
         def write_charset(format, charset):