Unified logging system for command-line programs

This unifies the various ad hoc logging (message printing, error
printing) systems used throughout the command-line programs.

Features:

- Program name is automatically prefixed.

- Message string does not end with newline.  This removes a common
  source of inconsistencies and omissions.

- Additionally, a final newline is automatically stripped, simplifying
  use of PQerrorMessage() etc., another common source of mistakes.

- I converted error message strings to use %m where possible.

- As a result of the above several points, more translatable message
  strings can be shared between different components and between
  frontends and backend, without gratuitous punctuation or whitespace
  differences.

- There is support for setting a "log level".  This is not meant to be
  user-facing, but can be used internally to implement debug or
  verbose modes.

- Lazy argument evaluation, so no significant overhead if logging at
  some level is disabled.

- Some color in the messages, similar to gcc and clang.  Set
  PG_COLOR=auto to try it out.  Some colors are predefined, but can be
  customized by setting PG_COLORS.

- Common files (common/, fe_utils/, etc.) can handle logging much more
  simply by just using one API without worrying too much about the
  context of the calling program, requiring callbacks, or having to
  pass "progname" around everywhere.

- Some programs called setvbuf() to make sure that stderr is
  unbuffered, even on Windows.  But not all programs did that.  This
  is now done centrally.

Soft goals:

- Reduces vertical space use and visual complexity of error reporting
  in the source code.

- Encourages more deliberate classification of messages.  For example,
  in some cases it wasn't clear without analyzing the surrounding code
  whether a message was meant as an error or just an info.

- Concepts and terms are vaguely aligned with popular logging
  frameworks such as log4j and Python logging.

This is all just about printing stuff out.  Nothing affects program
flow (e.g., fatal exits).  The uses are just too varied to do that.
Some existing code had wrappers that do some kind of print-and-exit,
and I adapted those.

I tried to keep the output mostly the same, but there is a lot of
historical baggage to unwind and special cases to consider, and I
might not always have succeeded.  One significant change is that
pg_rewind used to write all error messages to stdout.  That is now
changed to stderr.

Reviewed-by: Donald Dong <xdong@csumb.edu>
Reviewed-by: Arthur Zakirov <a.zakirov@postgrespro.ru>
Discussion: https://www.postgresql.org/message-id/flat/6a609b43-4f57-7348-6480-bd022f924310@2ndquadrant.com

1 files changed, 19 insertions, 19 deletions

diff --git a/src/bin/pg_rewind/copy_fetch.c b/src/bin/pg_rewind/copy_fetch.c
index a283405f6c..3fd0404ddf 100644
--- a/src/bin/pg_rewind/copy_fetch.c
+++ b/src/bin/pg_rewind/copy_fetch.c
@@ -57,8 +57,8 @@ recurse_dir(const char *datadir, const char *parentpath,
 
 	xldir = opendir(fullparentpath);
 	if (xldir == NULL)
-		pg_fatal("could not open directory \"%s\": %s\n",
-				 fullparentpath, strerror(errno));
+		pg_fatal("could not open directory \"%s\": %m",
+				 fullparentpath);
 
 	while (errno = 0, (xlde = readdir(xldir)) != NULL)
 	{
@@ -86,8 +86,8 @@ recurse_dir(const char *datadir, const char *parentpath,
 				 */
 			}
 			else
-				pg_fatal("could not stat file \"%s\": %s\n",
-						 fullpath, strerror(errno));
+				pg_fatal("could not stat file \"%s\": %m",
+						 fullpath);
 		}
 
 		if (parentpath)
@@ -115,10 +115,10 @@ recurse_dir(const char *datadir, const char *parentpath,
 
 			len = readlink(fullpath, link_target, sizeof(link_target));
 			if (len < 0)
-				pg_fatal("could not read symbolic link \"%s\": %s\n",
-						 fullpath, strerror(errno));
+				pg_fatal("could not read symbolic link \"%s\": %m",
+						 fullpath);
 			if (len >= sizeof(link_target))
-				pg_fatal("symbolic link \"%s\" target is too long\n",
+				pg_fatal("symbolic link \"%s\" target is too long",
 						 fullpath);
 			link_target[len] = '\0';
 
@@ -133,19 +133,19 @@ recurse_dir(const char *datadir, const char *parentpath,
 				strcmp(path, "pg_wal") == 0)
 				recurse_dir(datadir, path, callback);
 #else
-			pg_fatal("\"%s\" is a symbolic link, but symbolic links are not supported on this platform\n",
+			pg_fatal("\"%s\" is a symbolic link, but symbolic links are not supported on this platform",
 					 fullpath);
 #endif							/* HAVE_READLINK */
 		}
 	}
 
 	if (errno)
-		pg_fatal("could not read directory \"%s\": %s\n",
-				 fullparentpath, strerror(errno));
+		pg_fatal("could not read directory \"%s\": %m",
+				 fullparentpath);
 
 	if (closedir(xldir))
-		pg_fatal("could not close directory \"%s\": %s\n",
-				 fullparentpath, strerror(errno));
+		pg_fatal("could not close directory \"%s\": %m",
+				 fullparentpath);
 }
 
 /*
@@ -164,11 +164,11 @@ rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
 
 	srcfd = open(srcpath, O_RDONLY | PG_BINARY, 0);
 	if (srcfd < 0)
-		pg_fatal("could not open source file \"%s\": %s\n",
-				 srcpath, strerror(errno));
+		pg_fatal("could not open source file \"%s\": %m",
+				 srcpath);
 
 	if (lseek(srcfd, begin, SEEK_SET) == -1)
-		pg_fatal("could not seek in source file: %s\n", strerror(errno));
+		pg_fatal("could not seek in source file: %m");
 
 	open_target_file(path, trunc);
 
@@ -185,17 +185,17 @@ rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
 		readlen = read(srcfd, buf.data, len);
 
 		if (readlen < 0)
-			pg_fatal("could not read file \"%s\": %s\n",
-					 srcpath, strerror(errno));
+			pg_fatal("could not read file \"%s\": %m",
+					 srcpath);
 		else if (readlen == 0)
-			pg_fatal("unexpected EOF while reading file \"%s\"\n", srcpath);
+			pg_fatal("unexpected EOF while reading file \"%s\"", srcpath);
 
 		write_target_range(buf.data, begin, readlen);
 		begin += readlen;
 	}
 
 	if (close(srcfd) != 0)
-		pg_fatal("could not close file \"%s\": %s\n", srcpath, strerror(errno));
+		pg_fatal("could not close file \"%s\": %m", srcpath);
 }
 
 /*