fix -Wmissing-prototypes for neon extension (#7010)

## Problem

ref #6188

## Summary of changes

This pull request fixes `-Wmissing-prototypes` for the neon extension.
Note that (1) the gcc version in CI and macOS is different, therefore
some of the warning does not get reported when developing the neon
extension locally. (2) the CI env variable `COPT = -Werror` does not get
passed into the docker build process, therefore warnings are not treated
as errors on CI.


https://github.com/neondatabase/neon/blob/e62baa97041e10ce45772b3724e24e679a650d69/.github/workflows/build_and_test.yml#L22

There will be follow-up pull requests on solving other warnings. By the
way, I did not figure out the default compile parameters in the CI env,
and therefore this pull request is tested by manually adding
`-Wmissing-prototypes` into the `COPT`.

Signed-off-by: Alex Chi Z <chi@neon.tech>

pgxn/neon/control_plane_connector.c

@@ -35,6 +35,7 @@
 #include "utils/memutils.h"
 #include "utils/jsonb.h"
 
+#include "control_plane_connector.h"
 #include "neon_utils.h"
 
 static ProcessUtility_hook_type PreviousProcessUtilityHook = NULL;
@@ -113,16 +114,15 @@ ConstructDeltaMessage()
 	if (RootTable.db_table)
 	{
 		JsonbValue	dbs;
+		HASH_SEQ_STATUS status;
+		DbEntry    *entry;
 
 		dbs.type = jbvString;
 		dbs.val.string.val = "dbs";
 		dbs.val.string.len = strlen(dbs.val.string.val);
 		pushJsonbValue(&state, WJB_KEY, &dbs);
 		pushJsonbValue(&state, WJB_BEGIN_ARRAY, NULL);
 
-		HASH_SEQ_STATUS status;
-		DbEntry    *entry;
-
 		hash_seq_init(&status, RootTable.db_table);
 		while ((entry = hash_seq_search(&status)) != NULL)
 		{
@@ -168,8 +168,9 @@ ConstructDeltaMessage()
 #else
 				const char *logdetail;
 #endif
+				char	   *encrypted_password;
 				PushKeyValue(&state, "password", (char *) entry->password);
-				char	   *encrypted_password = get_role_password(entry->name, &logdetail);
+				encrypted_password = get_role_password(entry->name, &logdetail);
 
 				if (encrypted_password)
 				{
@@ -831,7 +832,7 @@ NeonProcessUtility(
 	}
 }
 
-extern void
+void
 InitControlPlaneConnector()
 {
 	PreviousProcessUtilityHook = ProcessUtility_hook;

pgxn/neon/control_plane_connector.h

@@ -1,6 +1,6 @@
 #ifndef CONTROL_PLANE_CONNECTOR_H
 #define CONTROL_PLANE_CONNECTOR_H
 
-void		InitControlPlaneConnector();
+void		InitControlPlaneConnector(void);
 
 #endif

pgxn/neon/extension_server.c

@@ -14,6 +14,7 @@
 
 #include "utils/guc.h"
 
+#include "extension_server.h" 
 #include "neon_utils.h"
 
 static int	extension_server_port = 0;

pgxn/neon/extension_server.h

@@ -0,0 +1,17 @@
+/*-------------------------------------------------------------------------
+ *
+ * extension_server.h
+ *	  Request compute_ctl to download extension files.
+ *
+ * IDENTIFICATION
+ *	 contrib/neon/extension_server.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef EXTENSION_SERVER_H
+#define EXTENSION_SERVER_H
+
+void pg_init_extension_server(void);
+
+#endif							/* EXTENSION_SERVER_H */

pgxn/neon/neon.c

@@ -29,6 +29,7 @@
 #include "utils/guc.h"
 #include "utils/wait_event.h"
 
+#include "extension_server.h"
 #include "neon.h"
 #include "walproposer.h"
 #include "pagestore_client.h"

pgxn/neon/neon.h

@@ -25,12 +25,11 @@ extern int	wal_acceptor_connection_timeout;
 extern void pg_init_libpagestore(void);
 extern void pg_init_walproposer(void);
 
-extern void pg_init_extension_server(void);
-
 extern uint64 BackpressureThrottlingTime(void);
 extern void replication_feedback_get_lsns(XLogRecPtr *writeLsn, XLogRecPtr *flushLsn, XLogRecPtr *applyLsn);
 
 extern void PGDLLEXPORT WalProposerSync(int argc, char *argv[]);
 extern void PGDLLEXPORT WalProposerMain(Datum main_arg);
+PGDLLEXPORT void LogicalSlotsMonitorMain(Datum main_arg);
 
 #endif							/* NEON_H */

pgxn/neon/neon_utils.c

@@ -6,6 +6,7 @@
 
 #include "postgres.h"
 
+#include "neon_utils.h"
 #include "lib/stringinfo.h"
 #include "libpq/pqformat.h"
 
@@ -14,7 +15,7 @@
  *
  * Returns -1 if the character is not a hexadecimal digit.
  */
-int
+static int
 HexDecodeChar(char c)
 {
 	if (c >= '0' && c <= '9')

pgxn/neon/neon_utils.h

@@ -12,7 +12,7 @@ uint32		pq_getmsgint32_le(StringInfo msg);
 uint64		pq_getmsgint64_le(StringInfo msg);
 void		pq_sendint32_le(StringInfo buf, uint32 i);
 void		pq_sendint64_le(StringInfo buf, uint64 i);
-extern void disable_core_dump();
+void        disable_core_dump(void);
 
 #ifndef WALPROPOSER_LIB
 

pgxn/neon/walproposer.c

@@ -1460,7 +1460,7 @@ RecvAppendResponses(Safekeeper *sk)
 }
 
 /* Parse a PageserverFeedback message, or the PageserverFeedback part of an AppendResponse */
-void
+static void
 ParsePageserverFeedbackMessage(WalProposer *wp, StringInfo reply_message, PageserverFeedback *rf)
 {
 	uint8		nkeys;
@@ -1590,9 +1590,9 @@ GetAcknowledgedByQuorumWALPosition(WalProposer *wp)
 Safekeeper *
 GetDonor(WalProposer *wp, XLogRecPtr *donor_lsn)
 {
-	*donor_lsn = InvalidXLogRecPtr;
 	Safekeeper *donor = NULL;
 	int			i;
+	*donor_lsn = InvalidXLogRecPtr;
 
 	if (wp->n_votes < wp->quorum)
 	{

pgxn/neon/walproposer_pg.c

@@ -398,7 +398,7 @@ walprop_pg_get_shmem_state(WalProposer *wp)
 	return walprop_shared;
 }
 
-void
+static void
 replication_feedback_set(PageserverFeedback *rf)
 {
 	SpinLockAcquire(&walprop_shared->mutex);