plugins: fix false-positive memleak.

This moves field initialization into plugins_new(), and
adds a memleak helper to search the request map:

=================================== ERRORS ====================================
___________________ ERROR at teardown of test_plugin_command ___________________
[gw0] linux -- Python 3.7.1 /opt/python/3.7.1/bin/python3.7
>       lambda: ihook(item=item, **kwds),
        when=when,
    )
../../../.local/lib/python3.7/site-packages/flaky/flaky_pytest_plugin.py:306:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
tests/fixtures.py:112: in node_factory
    ok = nf.killall([not n.may_fail for n in nf.nodes])
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
self = <utils.NodeFactory object at 0x7f873b245278>, expected_successes = [True]
    def killall(self, expected_successes):
        """Returns true if every node we expected to succeed actually succeeded""
        unexpected_fail = False
        for i in range(len(self.nodes)):
            leaks = None
            # leak detection upsets VALGRIND by reading uninitialized mem.
            # If it's dead, we'll catch it below.
            if not VALGRIND:
                try:
                    # This also puts leaks in log.
                    leaks = self.nodes[i].rpc.dev_memleak()['leaks']
                except Exception:
                    pass

            try:
                self.nodes[i].stop()
            except Exception:
                if expected_successes[i]:
                    unexpected_fail = True

            if leaks is not None and len(leaks) != 0:
                raise Exception("Node {} has memory leaks: {}".format(
                    self.nodes[i].daemon.lightning_dir,
>                   json.dumps(leaks, sort_keys=True, indent=4)
                ))
E               Exception: Node /tmp/ltests-qm87my20/test_plugin_command_1/lightnng-1/ has memory leaks: [
E                   {
E                       "backtrace": [
E                           "ccan/ccan/tal/tal.c:437 (tal_alloc_)",
E                           "lightningd/jsonrpc.c:1112 (jsonrpc_request_start_)",
E                           "lightningd/plugin.c:1041 (plugin_config)",
E                           "lightningd/plugin.c:1072 (plugins_config)",
E                           "lightningd/plugin.c:846 (plugin_manifest_cb)",
E                           "lightningd/plugin.c:252 (plugin_response_handle)",
E                           "lightningd/plugin.c:342 (plugin_read_json_one)",
E                           "lightningd/plugin.c:367 (plugin_read_json)",
E                           "ccan/ccan/io/io.c:59 (next_plan)",
E                           "ccan/ccan/io/io.c:407 (do_plan)",
E                           "ccan/ccan/io/io.c:417 (io_ready)",
E                           "ccan/ccan/io/poll.c:445 (io_loop)",
E                           "lightningd/io_loop_with_timers.c:24 (io_loop_with_tiers)",
E                           "lightningd/lightningd.c:840 (main)"
E                       ],
E                       "label": "lightningd/jsonrpc.c:1112:struct jsonrpc_reques",
E                       "parents": [
E                           "lightningd/plugin.c:66:struct plugin",
E                           "lightningd/lightningd.c:103:struct lightningd"
E                       ],
E                       "value": "0x55d6385e4088"
E                   },
E                   {
E                       "backtrace": [
E                           "ccan/ccan/tal/tal.c:437 (tal_alloc_)",
E                           "lightningd/jsonrpc.c:1112 (jsonrpc_request_start_)",
E                           "lightningd/plugin.c:1041 (plugin_config)",
E                           "lightningd/plugin.c:1072 (plugins_config)",
E                           "lightningd/plugin.c:846 (plugin_manifest_cb)",
E                           "lightningd/plugin.c:252 (plugin_response_handle)",
E                           "lightningd/plugin.c:342 (plugin_read_json_one)",
E                           "lightningd/plugin.c:367 (plugin_read_json)",
E                           "ccan/ccan/io/io.c:59 (next_plan)",
E                           "ccan/ccan/io/io.c:407 (do_plan)",
E                           "ccan/ccan/io/io.c:417 (io_ready)",
E                           "ccan/ccan/io/poll.c:445 (io_loop)",
E                           "lightningd/io_loop_with_timers.c:24 (io_loop_with_tiers)",
E                           "lightningd/lightningd.c:840 (main)"
E                       ],
E                       "label": "lightningd/jsonrpc.c:1112:struct jsonrpc_reques",
E                       "parents": [
E                           "lightningd/plugin.c:66:struct plugin",
E                           "lightningd/lightningd.c:103:struct lightningd"
E                       ],
E                       "value": "0x55d6386529d8"
E                   }
E               ]

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/plugin.c

@@ -33,6 +33,14 @@
  * `getmanifest` call anyway, that's what `init `is for. */
 #define PLUGIN_MANIFEST_TIMEOUT 60
 
+#if DEVELOPER
+static void memleak_help_pending_requests(struct htable *memtable,
+					  struct plugins *plugins)
+{
+	memleak_remove_uintmap(memtable, &plugins->pending_requests);
+}
+#endif /* DEVELOPER */
+
 struct plugins *plugins_new(const tal_t *ctx, struct log_book *log_book,
 			    struct lightningd *ld)
 {
@@ -42,6 +50,9 @@ struct plugins *plugins_new(const tal_t *ctx, struct log_book *log_book,
 	p->log_book = log_book;
 	p->log = new_log(p, log_book, "plugin-manager");
 	p->ld = ld;
+	uintmap_init(&p->pending_requests);
+	memleak_add_helper(p, memleak_help_pending_requests);
+
 	return p;
 }
 
@@ -1007,8 +1018,6 @@ void plugins_start(struct plugins *plugins, const char *dev_plugin_debug)
 void plugins_init(struct plugins *plugins, const char *dev_plugin_debug)
 {
 	plugins->pending_manifests = 0;
-	uintmap_init(&plugins->pending_requests);
-
 	plugins_add_default_dir(plugins,
 				path_join(tmpctx, plugins->ld->config_dir, "plugins"));