Improve common/logging.c's support for multiple verbosity levels.

Instead of hard-wiring specific verbosity levels into the option
processing of client applications, invent pg_logging_increase_verbosity()
and encourage clients to implement --verbose by calling that.  Then,
the common convention that more -v's gets you more verbosity just works.

In particular, this allows resurrection of the debug-grade messages that
have long existed in pg_dump and its siblings.  They were unreachable
before this commit due to lack of a way to select PG_LOG_DEBUG logging
level.  (It appears that they may have been unreachable for some time
before common/logging.c was introduced, too, so I'm not specifically
blaming cc8d41511 for the oversight.  One reason for thinking that is
that it's now apparent that _allocAH()'s message needs a null-pointer
guard.  Testing might have failed to reveal that before 96bf88d52.)

Discussion: https://postgr.es/m/1173106.1600116625@sss.pgh.pa.us

doc/src/sgml/ref/pg_dump.sgml

@@ -594,6 +594,8 @@ PostgreSQL documentation
         <application>pg_dump</application> to output detailed object
         comments and start/stop times to the dump file, and progress
         messages to standard error.
+        Repeating the option causes additional debug-level messages
+        to appear on standard error.
        </para>
       </listitem>
      </varlistentry>

doc/src/sgml/ref/pg_dumpall.sgml

@@ -202,7 +202,9 @@ PostgreSQL documentation
         Specifies verbose mode.  This will cause
         <application>pg_dumpall</application> to output start/stop
         times to the dump file, and progress messages to standard error.
-        It will also enable verbose output in <application>pg_dump</application>.
+        Repeating the option causes additional debug-level messages
+        to appear on standard error.
+        The option is also passed down to <application>pg_dump</application>.
        </para>
       </listitem>
      </varlistentry>

doc/src/sgml/ref/pg_restore.sgml

@@ -483,7 +483,12 @@ PostgreSQL documentation
       <term><option>--verbose</option></term>
       <listitem>
        <para>
-        Specifies verbose mode.
+        Specifies verbose mode.  This will cause
+        <application>pg_restore</application> to output detailed object
+        comments and start/stop times to the output file, and progress
+        messages to standard error.
+        Repeating the option causes additional debug-level messages
+        to appear on standard error.
        </para>
       </listitem>
      </varlistentry>

src/bin/pg_archivecleanup/pg_archivecleanup.c

@@ -302,7 +302,7 @@ main(int argc, char **argv)
 		switch (c)
 		{
 			case 'd':			/* Debug mode */
-				pg_logging_set_level(PG_LOG_DEBUG);
+				pg_logging_increase_verbosity();
 				break;
 			case 'n':			/* Dry-Run mode */
 				dryrun = true;

src/bin/pg_dump/pg_backup_archiver.c

@@ -2278,7 +2278,8 @@ _allocAH(const char *FileSpec, const ArchiveFormat fmt,
 {
 	ArchiveHandle *AH;
 
-	pg_log_debug("allocating AH for %s, format %d", FileSpec, fmt);
+	pg_log_debug("allocating AH for %s, format %d",
+				 FileSpec ? FileSpec : "(stdio)", fmt);
 
 	AH = (ArchiveHandle *) pg_malloc0(sizeof(ArchiveHandle));
 

src/bin/pg_dump/pg_dump.c

@@ -512,7 +512,7 @@ main(int argc, char **argv)
 
 			case 'v':			/* verbose */
 				g_verbose = true;
-				pg_logging_set_level(PG_LOG_INFO);
+				pg_logging_increase_verbosity();
 				break;
 
 			case 'w':

src/bin/pg_dump/pg_dumpall.c

@@ -283,7 +283,7 @@ main(int argc, char *argv[])
 
 			case 'v':
 				verbose = true;
-				pg_logging_set_level(PG_LOG_INFO);
+				pg_logging_increase_verbosity();
 				appendPQExpBufferStr(pgdumpopts, " -v");
 				break;
 

src/bin/pg_dump/pg_restore.c

@@ -245,7 +245,7 @@ main(int argc, char **argv)
 
 			case 'v':			/* verbose */
 				opts->verbose = 1;
-				pg_logging_set_level(PG_LOG_INFO);
+				pg_logging_increase_verbosity();
 				break;
 
 			case 'w':

src/bin/pg_rewind/pg_rewind.c

@@ -181,7 +181,7 @@ main(int argc, char **argv)
 
 			case 3:
 				debug = true;
-				pg_logging_set_level(PG_LOG_DEBUG);
+				pg_logging_increase_verbosity();
 				break;
 
 			case 'D':			/* -D or --target-pgdata */

src/bin/pgbench/pgbench.c

@@ -5522,7 +5522,7 @@ main(int argc, char **argv)
 				pgport = pg_strdup(optarg);
 				break;
 			case 'd':
-				pg_logging_set_level(PG_LOG_DEBUG);
+				pg_logging_increase_verbosity();
 				break;
 			case 'c':
 				benchmarking_option_set = true;

src/common/logging.c

@@ -157,12 +157,30 @@ pg_logging_config(int new_flags)
 	log_flags = new_flags;
 }
 
+/*
+ * pg_logging_init sets the default log level to INFO.  Programs that prefer
+ * a different default should use this to set it, immediately afterward.
+ */
 void
 pg_logging_set_level(enum pg_log_level new_level)
 {
 	__pg_log_level = new_level;
 }
 
+/*
+ * Command line switches such as --verbose should invoke this.
+ */
+void
+pg_logging_increase_verbosity(void)
+{
+	/*
+	 * The enum values are chosen such that we have to decrease __pg_log_level
+	 * in order to become more verbose.
+	 */
+	if (__pg_log_level > PG_LOG_NOTSET + 1)
+		__pg_log_level--;
+}
+
 void
 pg_logging_set_pre_callback(void (*cb) (void))
 {

src/include/common/logging.h

@@ -66,6 +66,7 @@ extern enum pg_log_level __pg_log_level;
 void		pg_logging_init(const char *argv0);
 void		pg_logging_config(int new_flags);
 void		pg_logging_set_level(enum pg_log_level new_level);
+void		pg_logging_increase_verbosity(void);
 void		pg_logging_set_pre_callback(void (*cb) (void));
 void		pg_logging_set_locus_callback(void (*cb) (const char **filename, uint64 *lineno));