Remove HAVE_UNIX_SOCKETS.

Since HAVE_UNIX_SOCKETS is now defined unconditionally, remove the macro
and drop a small amount of dead code.

The last known systems not to have them (as far as I know at least) were
QNX, which we de-supported years ago, and Windows, which now has them.

If a new OS ever shows up with the POSIX sockets API but without working
AF_UNIX, it'll presumably still be able to compile the code, and fail at
runtime with an unsupported address family error.  We might want to
consider adding a HINT that you should turn off the option to use it if
your network stack doesn't support it at that point, but it doesn't seem
worth making the relevant code conditional at compile time.

Also adjust a couple of places in the docs and comments that referred to
builds without Unix-domain sockets, since there aren't any.  Windows
still gets a special mention in those places, though, because we don't
try to use them by default there yet.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/CA%2BhUKG%2BL_3brvh%3D8e0BW_VfX9h7MtwgN%3DnFHP5o7X2oZucY9dg%40mail.gmail.com

src/backend/libpq/hba.c

@@ -973,17 +973,7 @@ parse_hba_line(TokenizedAuthLine *tok_line, int elevel)
 	token = linitial(tokens);
 	if (strcmp(token->string, "local") == 0)
 	{
-#ifdef HAVE_UNIX_SOCKETS
 		parsedline->conntype = ctLocal;
-#else
-		ereport(elevel,
-				(errcode(ERRCODE_CONFIG_FILE_ERROR),
-				 errmsg("local connections are not supported by this build"),
-				 errcontext("line %d of configuration file \"%s\"",
-							line_num, HbaFileName)));
-		*err_msg = "local connections are not supported by this build";
-		return NULL;
-#endif
 	}
 	else if (strcmp(token->string, "host") == 0 ||
 			 strcmp(token->string, "hostssl") == 0 ||

src/backend/libpq/pqcomm.c

@@ -149,10 +149,8 @@ static void socket_putmessage_noblock(char msgtype, const char *s, size_t len);
 static int	internal_putbytes(const char *s, size_t len);
 static int	internal_flush(void);
 
-#ifdef HAVE_UNIX_SOCKETS
 static int	Lock_AF_UNIX(const char *unixSocketDir, const char *unixSocketPath);
 static int	Setup_AF_UNIX(const char *sock_path);
-#endif							/* HAVE_UNIX_SOCKETS */
 
 static const PQcommMethods PqCommSocketMethods = {
 	socket_comm_reset,
@@ -334,10 +332,7 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 	struct addrinfo hint;
 	int			listen_index = 0;
 	int			added = 0;
-
-#ifdef HAVE_UNIX_SOCKETS
 	char		unixSocketPath[MAXPGPATH];
-#endif
 #if !defined(WIN32) || defined(IPV6_V6ONLY)
 	int			one = 1;
 #endif
@@ -348,7 +343,6 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 	hint.ai_flags = AI_PASSIVE;
 	hint.ai_socktype = SOCK_STREAM;
 
-#ifdef HAVE_UNIX_SOCKETS
 	if (family == AF_UNIX)
 	{
 		/*
@@ -369,7 +363,6 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 		service = unixSocketPath;
 	}
 	else
-#endif							/* HAVE_UNIX_SOCKETS */
 	{
 		snprintf(portNumberStr, sizeof(portNumberStr), "%d", portNumber);
 		service = portNumberStr;
@@ -427,11 +420,9 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 				familyDesc = _("IPv6");
 				break;
 #endif
-#ifdef HAVE_UNIX_SOCKETS
 			case AF_UNIX:
 				familyDesc = _("Unix");
 				break;
-#endif
 			default:
 				snprintf(familyDescBuf, sizeof(familyDescBuf),
 						 _("unrecognized address family %d"),
@@ -441,11 +432,9 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 		}
 
 		/* set up text form of address for log messages */
-#ifdef HAVE_UNIX_SOCKETS
 		if (addr->ai_family == AF_UNIX)
 			addrDesc = unixSocketPath;
 		else
-#endif
 		{
 			pg_getnameinfo_all((const struct sockaddr_storage *) addr->ai_addr,
 							   addr->ai_addrlen,
@@ -540,7 +529,6 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 			continue;
 		}
 
-#ifdef HAVE_UNIX_SOCKETS
 		if (addr->ai_family == AF_UNIX)
 		{
 			if (Setup_AF_UNIX(service) != STATUS_OK)
@@ -549,7 +537,6 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 				break;
 			}
 		}
-#endif
 
 		/*
 		 * Select appropriate accept-queue length limit.  PG_SOMAXCONN is only
@@ -572,13 +559,11 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 			continue;
 		}
 
-#ifdef HAVE_UNIX_SOCKETS
 		if (addr->ai_family == AF_UNIX)
 			ereport(LOG,
 					(errmsg("listening on Unix socket \"%s\"",
 							addrDesc)));
 		else
-#endif
 			ereport(LOG,
 			/* translator: first %s is IPv4 or IPv6 */
 					(errmsg("listening on %s address \"%s\", port %d",
@@ -597,8 +582,6 @@ StreamServerPort(int family, const char *hostName, unsigned short portNumber,
 }
 
 
-#ifdef HAVE_UNIX_SOCKETS
-
 /*
  * Lock_AF_UNIX -- configure unix socket file path
  */
@@ -699,7 +682,6 @@ Setup_AF_UNIX(const char *sock_path)
 	}
 	return STATUS_OK;
 }
-#endif							/* HAVE_UNIX_SOCKETS */
 
 
 /*

src/backend/postmaster/postmaster.c

@@ -1297,7 +1297,6 @@ PostmasterMain(int argc, char *argv[])
 	}
 #endif
 
-#ifdef HAVE_UNIX_SOCKETS
 	if (Unix_socket_directories)
 	{
 		char	   *rawstring;
@@ -1347,7 +1346,6 @@ PostmasterMain(int argc, char *argv[])
 		list_free_deep(elemlist);
 		pfree(rawstring);
 	}
-#endif
 
 	/*
 	 * check that we have some socket to listen on

src/backend/utils/misc/guc.c

@@ -4452,11 +4452,7 @@ static struct config_string ConfigureNamesString[] =
 			GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY
 		},
 		&Unix_socket_directories,
-#ifdef HAVE_UNIX_SOCKETS
 		DEFAULT_PGSOCKET_DIR,
-#else
-		"",
-#endif
 		NULL, NULL, NULL
 	},