add a podman-compose command

**podman compose** is a thin wrapper around an external compose provider
such as docker-compose or podman-compose.  This means that `podman
compose` is executing another tool that implements the compose
functionality but sets up the environment in a way to let the compose
provider communicate transparently with the local Podman socket.  The
specified options as well the command and argument are passed directly
to the compose provider.

The default compose providers are `docker-compose` and `podman-compose`.
If installed, `docker-compose` takes precedence since it is the original
implementation of the Compose specification and is widely used on the
supported platforms (i.e., Linux, Mac OS, Windows).

If you want to change the default behavior or have a custom installation
path for your provider of choice, please change the `compose_provider`
field in `containers.conf(5)`.  You may also set the
`PODMAN_COMPOSE_PROVIDER` environment variable.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

test/system/015-help.bats

@@ -17,6 +17,11 @@ function check_help() {
     local -A found
 
     for cmd in $(_podman_commands "$@"); do
+        # Skip the compose command which is calling `docker-compose --help`
+        # and hence won't match the assumptions made below.
+        if [[ "$cmd" == "compose" ]]; then
+            continue
+        fi
         # Human-readable podman command string, with multiple spaces collapsed
         command_string="podman $* $cmd"
         command_string=${command_string//  / }  # 'podman  x' -> 'podman x'

test/system/600-completion.bats

@@ -37,6 +37,11 @@ function check_shell_completion() {
 "
 
     for cmd in $(_podman_commands "$@"); do
+        # Skip the compose command which is calling `docker-compose --help`
+        # and hence won't match the assumptions made below.
+        if [[ "$cmd" == "compose" ]]; then
+            continue
+        fi
         # Human-readable podman command string, with multiple spaces collapsed
         name="podman"
         if is_remote; then

test/system/610-format.bats

@@ -55,6 +55,12 @@ can_run_stats=
 #        > run the command with --format '{{"\n"}}' and make sure it passes
 function check_subcommand() {
     for cmd in $(_podman_commands "$@"); do
+        # Skip the compose command which is calling `docker-compose --help`
+        # and hence won't match the assumptions made below.
+        if [[ "$cmd" == "compose" ]]; then
+            continue
+        fi
+        # Human-readable podman command string, with multiple spaces collapsed
         # Special case: 'podman machine' can only be run under ideal conditions
         if [[ "$cmd" = "machine" ]] && [[ -z "$can_run_podman_machine" ]]; then
             continue

test/system/850-compose.bats

@@ -0,0 +1,67 @@
+#!/usr/bin/env bats   -*- bats -*-
+#
+# Smoke tests for the podman-compose command.  test/compose takes care of functional tests.
+#
+
+load helpers
+
+@test "podman compose - smoke tests" {
+    fake_compose_bin="$PODMAN_TMPDIR/fake_compose"
+    cat >$fake_compose_bin <<EOF
+#!/bin/bash
+if [[ "\$@" == "fail" ]]; then
+    exit 42
+fi
+if [[ "\$@" == "env" ]]; then
+    printenv DOCKER_HOST DOCKER_BUILDKIT DOCKER_CONFIG
+    exit 0
+fi
+echo "arguments: \$@"
+EOF
+
+    compose_conf="$PODMAN_TMPDIR/compose.conf"
+    cat >$compose_conf <<EOF
+[engine]
+compose_providers = ["$fake_compose_bin"]
+compose_warning_logs = false
+EOF
+
+    random_data="--foo=bar --random=$(random_string 15) -f /path/to/file ignore me"
+
+    # Make sure that the fake compose binary is used and that error reporting works
+    PODMAN_COMPOSE_PROVIDER=$fake_compose_bin run_podman 125 compose --help
+    is "$output" ".*executing $fake_compose_bin --help: .*: permission denied"
+
+    # Make the fake one executable and check the --help output
+    chmod +x $fake_compose_bin
+    PODMAN_COMPOSE_PROVIDER=$fake_compose_bin run_podman compose --help
+    is "$output" "Run compose workloads via an external provider .*arguments: --help"
+
+    # No argument yields the help message as well
+    PODMAN_COMPOSE_PROVIDER=$fake_compose_bin run_podman compose
+    is "$output" "Run compose workloads via an external provider .*arguments: "
+
+    # Make sure that the provider can be specified via containers.conf and that
+    # the warning logs can be turned off
+    CONTAINERS_CONF_OVERRIDE=$compose_conf run_podman compose --help
+    is "$output" "Run compose workloads via an external provider .*arguments: --help"
+    assert "$output" !~ ".*Executing external compose provider.*"
+
+    # Run with bogus arguments and make sure they're being returned
+    CONTAINERS_CONF_OVERRIDE=$compose_conf run_podman compose $random_data
+    is "$output" "arguments: $random_data"
+
+    # Make sure Podman returns the exit code of the compose provider
+    CONTAINERS_CONF_OVERRIDE=$compose_conf run_podman 42 compose fail
+
+    # Make sure the three env variables are set (and parsed)
+    CONTAINERS_CONF_OVERRIDE=$compose_conf run_podman compose env
+    is "${lines[0]}" ".*/podman.sock"
+    is "${lines[1]}" "0"
+    is "${lines[2]}" ""
+
+    DOCKER_HOST="$random_data" DOCKER_CONFIG="$random_data" CONTAINERS_CONF_OVERRIDE=$compose_conf run_podman compose env
+    is "${lines[0]}" "$random_data"
+    is "${lines[1]}" "0"
+    is "${lines[2]}" "$random_data"
+}