Update postgresHasDefault() error message to document libpq defaults

R/dbConnect_PqDriver.R

@@ -18,21 +18,27 @@
 #'   PostgreSQL(-ish) database or [Redshift()] to connect to an AWS Redshift
 #'   cluster. Use an existing [DBI::DBIConnection-class] object to clone an
 #'   existing connection.
-#' @param dbname Database name. If `NULL`, defaults to the user name.
+#' @param dbname Database name. If `NULL`, will be
+#'   retrieved from the `PGDATABASE` env var, or defaults to the user name.
 #'   Note that this argument can only contain the database name, it will not
 #'   be parsed as a connection string (internally, `expand_dbname` is set to
 #'   `false` in the call to
 #'   [`PQconnectdbParams()`](https://www.postgresql.org/docs/current/libpq-connect.html)).
 #' @param user,password User name and password. If `NULL`, will be
 #'   retrieved from `PGUSER` and `PGPASSWORD` envvars, or from the
-#'   appropriate line in `~/.pgpass`. See
-#'   <https://www.postgresql.org/docs/current/libpq-pgpass.html> for
+#'   appropriate line in `~/.pgpass`. If `PGUSER` is not set,
+#'   defaults to the operating system user name.
+#'   See <https://www.postgresql.org/docs/current/libpq-pgpass.html> for
 #'   more details.
 #' @param host,port Host and port. If `NULL`, will be retrieved from
-#'   `PGHOST` and `PGPORT` env vars.
+#'   `PGHOST` and `PGPORT` env vars. If those are not set either,
+#'   defaults to a local Unix-domain socket connection and port `5432`,
+#'   as documented in
+#'   [libpq connection parameter docs](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS).
 #' @param service Name of service to connect as.  If `NULL`, will be
-#'   ignored.  Otherwise, connection parameters will be loaded from the pg_service.conf
-#'   file and used.  See <https://www.postgresql.org/docs/current/libpq-pgservice.html>
+#'   retrieved from `PGSERVICE` env var.  If defined, connection parameters
+#'   will be loaded from the pg_service.conf file and used.  See
+#'   <https://www.postgresql.org/docs/current/libpq-pgservice.html>
 #'   for details on this file and syntax.
 #' @param ... Other name-value pairs that describe additional connection
 #'   options as described at

R/default.R

@@ -24,9 +24,11 @@ postgresHasDefault <- function(...) {
     error = function(...) {
       message(
         "Could not initialise default postgres database. If postgres is running\n",
-        "check that the environment variables PGHOST, PGPORT, \n",
-        "PGUSER, PGPASSWORD, and PGDATABASE, are defined and\n",
-        "point to your database."
+        "check that the connection works with default libpq settings.\n",
+        "The default connection uses the PGHOST, PGPORT, PGUSER, PGPASSWORD,\n",
+        "and PGDATABASE environment variables. If unset, libpq defaults are\n",
+        "used (local connection, port 5432, OS user name).\n",
+        "See https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS"
       )
       FALSE
     }