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

src/fe_utils/Makefile

@@ -19,7 +19,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -DFRONTEND -I$(libpq_srcdir) $(CPPFLAGS)
 
-OBJS = mbprint.o print.o psqlscan.o simple_list.o string_utils.o conditional.o
+OBJS = logging.o mbprint.o print.o psqlscan.o simple_list.o string_utils.o conditional.o
 
 all: libpgfeutils.a
 

src/fe_utils/logging.c

@@ -0,0 +1,228 @@
+/*-------------------------------------------------------------------------
+ * Logging framework for frontend programs
+ *
+ * Copyright (c) 2018, PostgreSQL Global Development Group
+ *
+ * src/fe_utils/logging.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres_fe.h"
+
+#include <unistd.h>
+
+#include "fe_utils/logging.h"
+
+static const char *progname;
+
+enum pg_log_level __pg_log_level;
+static int log_flags;
+void (*log_pre_callback)(void);
+void (*log_locus_callback)(const char **, uint64 *);
+
+static const char *sgr_error = NULL;
+static const char *sgr_warning = NULL;
+static const char *sgr_locus = NULL;
+
+#define SGR_ERROR_DEFAULT "01;31"
+#define SGR_WARNING_DEFAULT "01;35"
+#define SGR_LOCUS_DEFAULT "01"
+
+#define ANSI_ESCAPE_FMT "\x1b[%sm"
+#define ANSI_ESCAPE_RESET "\x1b[0m"
+
+/*
+ * This should be called before any output happens.
+ */
+void
+pg_logging_init(const char *argv0)
+{
+	const char *pg_color_env = getenv("PG_COLOR");
+	bool		log_color = false;
+
+	/* usually the default, but not on Windows */
+	setvbuf(stderr, NULL, _IONBF, 0);
+
+	progname = get_progname(argv0);
+	__pg_log_level = PG_LOG_INFO;
+
+	if (pg_color_env)
+	{
+		if (strcmp(pg_color_env, "always") == 0 ||
+			(strcmp(pg_color_env, "auto") == 0 && isatty(fileno(stderr))))
+			log_color = true;
+	}
+
+	if (log_color)
+	{
+		const char *pg_colors_env = getenv("PG_COLORS");
+
+		if (pg_colors_env)
+		{
+			char	 *colors = strdup(pg_colors_env);
+
+			if (colors)
+			{
+				for (char *token = strtok(colors, ":"); token; token = strtok(NULL, ":"))
+				{
+					char *e = strchr(token, '=');
+
+					if (e)
+					{
+						char	   *name;
+						char	   *value;
+
+						*e = '\0';
+						name = token;
+						value = e + 1;
+
+						if (strcmp(name, "error") == 0)
+							sgr_error = strdup(value);
+						if (strcmp(name, "warning") == 0)
+							sgr_warning = strdup(value);
+						if (strcmp(name, "locus") == 0)
+							sgr_locus = strdup(value);
+					}
+				}
+
+				free(colors);
+			}
+		}
+		else
+		{
+			sgr_error = SGR_ERROR_DEFAULT;
+			sgr_warning = SGR_WARNING_DEFAULT;
+			sgr_locus = SGR_LOCUS_DEFAULT;
+		}
+	}
+}
+
+void
+pg_logging_config(int new_flags)
+{
+	log_flags = new_flags;
+}
+
+void
+pg_logging_set_level(enum pg_log_level new_level)
+{
+	__pg_log_level = new_level;
+}
+
+void
+pg_logging_set_pre_callback(void (*cb)(void))
+{
+	log_pre_callback = cb;
+}
+
+void
+pg_logging_set_locus_callback(void (*cb)(const char **filename, uint64 *lineno))
+{
+	log_locus_callback = cb;
+}
+
+void
+pg_log_generic(enum pg_log_level level, const char * pg_restrict fmt, ...)
+{
+	va_list		ap;
+
+	va_start(ap, fmt);
+	pg_log_generic_v(level, fmt, ap);
+	va_end(ap);
+}
+
+void
+pg_log_generic_v(enum pg_log_level level, const char * pg_restrict fmt, va_list ap)
+{
+	int			save_errno = errno;
+	const char *filename = NULL;
+	uint64		lineno = 0;
+	va_list		ap2;
+	size_t		required_len;
+	char	   *buf;
+
+	Assert(progname);
+	Assert(level);
+	Assert(fmt);
+	Assert(fmt[strlen(fmt) - 1] != '\n');
+
+	fflush(stdout);
+	if (log_pre_callback)
+		log_pre_callback();
+
+	if (log_locus_callback)
+		log_locus_callback(&filename, &lineno);
+
+	fmt = _(fmt);
+
+	if (!(log_flags & PG_LOG_FLAG_TERSE) || filename)
+	{
+		if (sgr_locus)
+			fprintf(stderr, ANSI_ESCAPE_FMT, sgr_locus);
+		if (!(log_flags & PG_LOG_FLAG_TERSE))
+			fprintf(stderr, "%s:", progname);
+		if (filename)
+		{
+			fprintf(stderr, "%s:", filename);
+			if (lineno > 0)
+				fprintf(stderr, UINT64_FORMAT ":", lineno);
+		}
+		fprintf(stderr, " ");
+		if (sgr_locus)
+			fprintf(stderr, ANSI_ESCAPE_RESET);
+	}
+
+	if (!(log_flags & PG_LOG_FLAG_TERSE))
+	{
+		switch (level)
+		{
+			case PG_LOG_FATAL:
+				if (sgr_error)
+					fprintf(stderr, ANSI_ESCAPE_FMT, sgr_error);
+				fprintf(stderr, _("fatal: "));
+				if (sgr_error)
+					fprintf(stderr, ANSI_ESCAPE_RESET);
+				break;
+			case PG_LOG_ERROR:
+				if (sgr_error)
+					fprintf(stderr, ANSI_ESCAPE_FMT, sgr_error);
+				fprintf(stderr, _("error: "));
+				if (sgr_error)
+					fprintf(stderr, ANSI_ESCAPE_RESET);
+				break;
+			case PG_LOG_WARNING:
+				if (sgr_warning)
+					fprintf(stderr, ANSI_ESCAPE_FMT, sgr_warning);
+				fprintf(stderr, _("warning: "));
+				if (sgr_warning)
+					fprintf(stderr, ANSI_ESCAPE_RESET);
+				break;
+			default:
+				break;
+		}
+	}
+
+	errno = save_errno;
+
+	va_copy(ap2, ap);
+	required_len = vsnprintf(NULL, 0, fmt, ap2) + 1;
+	va_end(ap2);
+
+	buf = pg_malloc_extended(required_len, MCXT_ALLOC_NO_OOM);
+
+	if (!buf)
+	{
+		/* memory trouble, just print what we can and get out of here */
+		vfprintf(stderr, fmt, ap);
+		return;
+	}
+
+	vsnprintf(buf, required_len, fmt, ap);
+
+	/* strip one newline, for PQerrorMessage() */
+	if (buf[required_len - 2] == '\n')
+		buf[required_len - 2] = '\0';
+
+	fprintf(stderr, "%s\n", buf);
+	free(buf);
+}

src/fe_utils/psqlscan.l

@@ -34,6 +34,7 @@
  */
 #include "postgres_fe.h"
 
+#include "fe_utils/logging.h"
 #include "fe_utils/psqlscan.h"
 
 #include "libpq-fe.h"
@@ -725,7 +726,7 @@ other			.
 						if (psqlscan_var_is_current_source(cur_state, varname))
 						{
 							/* Recursive expansion --- don't go there */
-							cur_state->callbacks->write_error("skipping recursive expansion of variable \"%s\"\n",
+							pg_log_warning("skipping recursive expansion of variable \"%s\"",
 															  varname);
 							/* Instead copy the string as is */
 							ECHO;