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From: Jim Nasby <[email protected]>
To: Pg Hackers <[email protected]>
Subject: Improved error reporting in format()
Date: Sat, 2 Jan 2016 17:57:48 -0600
Message-ID: <[email protected]> (raw)
List-Unsubscribe: <mailto:[email protected]?body=unsub%20pgsql-hackers>

The current error message for an invalid format conversion type is 
extremely confusing except in the simplest of uses:

select format( '% moo');
ERROR:  unrecognized conversion type specifier " "

Obviously in that example you can figure out what's going on, but 
frequently format() is used in a complex context where it's not at all 
obvious that format is the problem. Even worse, "conversion" makes it 
sound like a localization issue.

Attached patch clarifies that %-related error messages with hints as 
well as (IMHO) improving the clarity of the message:

select format( '% moo');
ERROR:  unrecognized format() type specifier " "
HINT:  For a single "%" use "%%"

I also made the use of "format()" consistent in all the other error 
messages.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index a89f586..a4552ad 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -4647,7 +4647,8 @@ text_reverse(PG_FUNCTION_ARGS)
 		if (++(ptr) >= (end_ptr)) \
 			ereport(ERROR, \
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE), \
-					 errmsg("unterminated format specifier"))); \
+					 errmsg("unterminated format() type specifier"), \
+					 errhint("For a single \"%%\" use \"%%%%\"."))); \
 	} while (0)
 
 /*
@@ -4779,8 +4780,9 @@ text_format(PG_FUNCTION_ARGS)
 		if (strchr("sIL", *cp) == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("unrecognized conversion type specifier \"%c\"",
-							*cp)));
+					 errmsg("unrecognized format() type specifier \"%c\"",
+							*cp),
+					 errhint("For a single \"%%\" use \"%%%%\".")));
 
 		/* If indirect width was specified, get its value */
 		if (widthpos >= 0)
@@ -4791,7 +4793,7 @@ text_format(PG_FUNCTION_ARGS)
 			if (arg >= nargs)
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-						 errmsg("too few arguments for format")));
+						 errmsg("too few arguments for format()")));
 
 			/* Get the value and type of the selected argument */
 			if (!funcvariadic)
@@ -4899,8 +4901,9 @@ text_format(PG_FUNCTION_ARGS)
 				/* should not get here, because of previous check */
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					  errmsg("unrecognized conversion type specifier \"%c\"",
-							 *cp)));
+					  errmsg("unrecognized format() type specifier \"%c\"",
+							 *cp),
+					  errhint("For a single \"%%\" use \"%%%%\".")));
 				break;
 		}
 	}


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Attachments:

  [text/plain] patch.diff (1.7K, ../[email protected]/2-patch.diff)
  download | inline diff:
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index a89f586..a4552ad 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -4647,7 +4647,8 @@ text_reverse(PG_FUNCTION_ARGS)
 		if (++(ptr) >= (end_ptr)) \
 			ereport(ERROR, \
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE), \
-					 errmsg("unterminated format specifier"))); \
+					 errmsg("unterminated format() type specifier"), \
+					 errhint("For a single \"%%\" use \"%%%%\"."))); \
 	} while (0)
 
 /*
@@ -4779,8 +4780,9 @@ text_format(PG_FUNCTION_ARGS)
 		if (strchr("sIL", *cp) == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("unrecognized conversion type specifier \"%c\"",
-							*cp)));
+					 errmsg("unrecognized format() type specifier \"%c\"",
+							*cp),
+					 errhint("For a single \"%%\" use \"%%%%\".")));
 
 		/* If indirect width was specified, get its value */
 		if (widthpos >= 0)
@@ -4791,7 +4793,7 @@ text_format(PG_FUNCTION_ARGS)
 			if (arg >= nargs)
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-						 errmsg("too few arguments for format")));
+						 errmsg("too few arguments for format()")));
 
 			/* Get the value and type of the selected argument */
 			if (!funcvariadic)
@@ -4899,8 +4901,9 @@ text_format(PG_FUNCTION_ARGS)
 				/* should not get here, because of previous check */
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					  errmsg("unrecognized conversion type specifier \"%c\"",
-							 *cp)));
+					  errmsg("unrecognized format() type specifier \"%c\"",
+							 *cp),
+					  errhint("For a single \"%%\" use \"%%%%\".")));
 				break;
 		}
 	}


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