Donn't fallback for Postgres user and password values.

We were not comprehensive enough, failing to find data in the service file.
Best just to let libpq do the work, and not try to replicate it. The downside
is that users of the Docker image may be surprised to find that their default
username is `root` (or whatever the docker image username is(), so we'll just
have to document that behavior. Closes #410.

Changes

@@ -7,6 +7,11 @@ Revision history for Perl extension App::Sqitch
        `connections.dbname` variables in the SnowSQL configuration file
        (`~/.snowsql/config`) before falling back on the hard-coded warehouse
        name "sqitch" and using the system username as the database name.
+     - Removed fallback in the PostgreSQL engine on the `$PGUSER` and
+       `$PGPASSWORD` environnment variables, as well as the system username,
+       since libpq does all that automatically, and collects data from other
+       sources that we did not (e.g., the password and connection service
+       files). Thanks to Tom Bloor for the report (issue #410).
 
 0.9998 2018-10-03T20:53:58Z
      - Fixed an issue where Sqitch would sometimes truncate the registry

lib/App/Sqitch/Engine/pg.pm

@@ -28,12 +28,22 @@ sub destination {
     # Use the URI sans password, and with the database name added.
     my $uri = $self->target->uri->clone;
     $uri->password(undef) if $uri->password;
-    $uri->dbname( $ENV{PGDATABASE} || $self->username );
+    $uri->dbname(
+        $ENV{PGDATABASE}
+        || $self->username
+        || $ENV{PGUSER}
+        || $self->sqitch->sysuser
+    );
     return $uri->as_string;
 }
 
-sub _def_user { $ENV{PGUSER} || shift->sqitch->sysuser }
-sub _def_pass { $ENV{PGPASSWORD} }
+# DBD::pg and psql use fallbacks consistently, thanks to libpq. These include
+# environment variables, system info (username), the password file, and the
+# connection service file. Best for us not to second-guess these values,
+# though we admittedly try when setting the database name in the destination
+# URI for unnamed targets a few lines up from here.
+sub _def_user { }
+sub _def_pass { }
 
 has _psql => (
     is         => 'ro',

t/pg.t

@@ -64,15 +64,14 @@ my @std_opts = (
     '--set' => 'registry=sqitch',
 );
 my $sysuser = $sqitch->sysuser;
-is_deeply [$pg->psql], [$client, '--dbname', "user=$sysuser", @std_opts],
+is_deeply [$pg->psql], [$client, @std_opts],
     'psql command should be conninfo, and std opts-only';
 
 isa_ok $pg = $CLASS->new(sqitch => $sqitch, target => $target), $CLASS;
 ok $pg->set_variables(foo => 'baz', whu => 'hi there', yo => 'stellar'),
     'Set some variables';
 is_deeply [$pg->psql], [
     $client,
-    '--dbname', "user=$sysuser",
     '--set' => 'foo=baz',
     '--set' => 'whu=hi there',
     '--set' => 'yo=stellar',
@@ -84,18 +83,12 @@ is_deeply [$pg->psql], [
 ENV: {
     # Make sure we override system-set vars.
     local $ENV{PGDATABASE};
-    local $ENV{PGUSER};
-    local $ENV{PGPASSWORD};
     for my $env (qw(PGDATABASE PGUSER PGPASSWORD)) {
         my $pg = $CLASS->new(sqitch => $sqitch, target => $target);
         local $ENV{$env} = "\$ENV=whatever";
         is $pg->target->uri, "db:pg:", "Target should not read \$$env";
         is $pg->registry_destination, $pg->destination,
             'Registry target should be the same as destination';
-        is $pg->username, $ENV{PGUSER} || $sysuser,
-            "Should have username when $env set";
-        is $pg->password, $ENV{PGPASSWORD},
-            "Should have password when $env set";
     }
 
     my $mocker = Test::MockModule->new('App::Sqitch');
@@ -132,7 +125,7 @@ is $pg->registry, 'meta', 'registry should be as configured';
 is_deeply [$pg->psql], [
     '/path/to/psql',
     '--dbname',
-    "user=$sysuser dbname=try host=localhost connect_timeout=5 sslmode=disable",
+    "dbname=try host=localhost connect_timeout=5 sslmode=disable",
 @std_opts], 'psql command should be configured from URI config';
 
 ##############################################################################
@@ -155,7 +148,7 @@ is $pg->registry, 'meta', 'registry should still be as configured';
 is_deeply [$pg->psql], [
     '/some/other/psql',
     '--dbname',
-    "user=$sysuser dbname=try host=localhost connect_timeout=5 sslmode=disable",
+    "dbname=try host=localhost connect_timeout=5 sslmode=disable",
 @std_opts], 'psql command should be as optioned';
 
 ##############################################################################