Allow emit_log_hook to see original message text

emit_log_hook could only see the translated text, making it harder to identify
which message was being sent. Pass original text to allow the exact message to
be identified, whichever language is used for logging.

Discussion: 20160216.184755.59721141.horiguchi.kyotaro@lab.ntt.co.jp
Author: Kyotaro Horiguchi

src/backend/utils/error/elog.c

@@ -801,6 +801,7 @@ errmsg(const char *fmt,...)
 	CHECK_STACK_DEPTH();
 	oldcontext = MemoryContextSwitchTo(edata->assoc_context);
 
+	edata->message_id = fmt;
 	EVALUATE_MESSAGE(edata->domain, message, false, true);
 
 	MemoryContextSwitchTo(oldcontext);
@@ -830,6 +831,7 @@ errmsg_internal(const char *fmt,...)
 	CHECK_STACK_DEPTH();
 	oldcontext = MemoryContextSwitchTo(edata->assoc_context);
 
+	edata->message_id = fmt;
 	EVALUATE_MESSAGE(edata->domain, message, false, false);
 
 	MemoryContextSwitchTo(oldcontext);
@@ -853,6 +855,7 @@ errmsg_plural(const char *fmt_singular, const char *fmt_plural,
 	CHECK_STACK_DEPTH();
 	oldcontext = MemoryContextSwitchTo(edata->assoc_context);
 
+	edata->message_id = fmt_singular;
 	EVALUATE_MESSAGE_PLURAL(edata->domain, message, false);
 
 	MemoryContextSwitchTo(oldcontext);
@@ -1361,6 +1364,7 @@ elog_finish(int elevel, const char *fmt,...)
 	recursion_depth++;
 	oldcontext = MemoryContextSwitchTo(edata->assoc_context);
 
+	edata->message_id = fmt;
 	EVALUATE_MESSAGE(edata->domain, message, false, false);
 
 	MemoryContextSwitchTo(oldcontext);
@@ -1420,6 +1424,7 @@ format_elog_string(const char *fmt,...)
 
 	oldcontext = MemoryContextSwitchTo(ErrorContext);
 
+	edata->message_id = fmt;
 	EVALUATE_MESSAGE(edata->domain, message, false, true);
 
 	MemoryContextSwitchTo(oldcontext);
@@ -1458,6 +1463,11 @@ EmitErrorReport(void)
 	 * where it would have much less information available.  emit_log_hook is
 	 * intended for custom log filtering and custom log message transmission
 	 * mechanisms.
+	 *
+	 * The log hook has access to both the translated and original English
+	 * error message text, which is passed through to allow it to be used
+	 * as a message identifier. Note that the original text is not available
+	 * for detail, detail_log, hint and context text elements.
 	 */
 	if (edata->output_to_server && emit_log_hook)
 		(*emit_log_hook) (edata);

src/include/utils/elog.h

@@ -349,11 +349,12 @@ typedef struct ErrorData
 	const char *domain;			/* message domain */
 	const char *context_domain; /* message domain for context message */
 	int			sqlerrcode;		/* encoded ERRSTATE */
-	char	   *message;		/* primary error message */
+	char	   *message;		/* primary error message (translated) */
 	char	   *detail;			/* detail error message */
 	char	   *detail_log;		/* detail error message for server log only */
 	char	   *hint;			/* hint message */
 	char	   *context;		/* context message */
+	const char *message_id;		/* message id of .message (original English text) */
 	char	   *schema_name;	/* name of schema */
 	char	   *table_name;		/* name of table */
 	char	   *column_name;	/* name of column */