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Commite3a87b4

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Re-implement the ereport() macro using __VA_ARGS__.
Now that we require C99, we can depend on __VA_ARGS__ to work, andrevising ereport() to use it has several significant benefits:* The extra parentheses around the auxiliary function calls are nowoptional. Aside from being a bit less ugly, this removes a commongotcha for new contributors, because in some cases the compiler errorsyou got from forgetting them were unintelligible.* The auxiliary function calls are now evaluated as a comma expressionlist rather than as extra arguments to errfinish(). This means thatcompilers can be expected to warn about no-op expressions in the list,allowing detection of several other common mistakes such as forgettingto add errmsg(...) when converting an elog() call to ereport().* Unlike the situation with extra function arguments, comma expressionsare guaranteed to be evaluated left-to-right, so this removes platformdependency in the order of the auxiliary function calls. While thatdependency hasn't caused us big problems in the past, this change doesallow dropping some rather shaky assumptions around errcontext() domainhandling.There's no intention to make wholesale changes of existing ereportcalls, but as proof-of-concept this patch removes the extra parensfrom a couple of calls in postgres.c.While new code can be written either way, code intended to beback-patched will need to use extra parens for awhile yet. It seemsworth back-patching this change into v12, so as to reduce the windowwhere we have to be careful about that by one year. Hence, this patchis careful to preserve ABI compatibility; a followup HEAD-only patchwill make some additional simplifications.Andres Freund and Tom LaneDiscussion:https://postgr.es/m/CA+fd4k6N8EjNvZpM8nme+y+05mz-SM8Z_BgkixzkA34R+ej0Kw@mail.gmail.com
1 parentcef27ae commite3a87b4

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4 files changed

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-42
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4 files changed

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‎doc/src/sgml/sources.sgml

Lines changed: 30 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -103,9 +103,9 @@ less -x4
103103
message text. In addition there are optional elements, the most
104104
common of which is an error identifier code that follows the SQL spec's
105105
SQLSTATE conventions.
106-
<function>ereport</function> itself is just a shellfunction, that exists
106+
<function>ereport</function> itself is just a shellmacro, that exists
107107
mainly for the syntactic convenience of making message generation
108-
look like a function call in the C source code. The only parameter
108+
look like asinglefunction call in the C source code. The only parameter
109109
accepted directly by <function>ereport</function> is the severity level.
110110
The primary message text and any optional message elements are
111111
generated by calling auxiliary functions, such as <function>errmsg</function>,
@@ -116,36 +116,50 @@ less -x4
116116
A typical call to <function>ereport</function> might look like this:
117117
<programlisting>
118118
ereport(ERROR,
119-
(errcode(ERRCODE_DIVISION_BY_ZERO),
120-
errmsg("division by zero")));
119+
errcode(ERRCODE_DIVISION_BY_ZERO),
120+
errmsg("division by zero"));
121121
</programlisting>
122122
This specifies error severity level <literal>ERROR</literal> (a run-of-the-mill
123123
error). The <function>errcode</function> call specifies the SQLSTATE error code
124124
using a macro defined in <filename>src/include/utils/errcodes.h</filename>. The
125-
<function>errmsg</function> call provides the primary message text. Notice the
126-
extra set of parentheses surrounding the auxiliary function calls &mdash;
127-
these are annoying but syntactically necessary.
125+
<function>errmsg</function> call provides the primary message text.
126+
</para>
127+
128+
<para>
129+
You will also frequently see this older style, with an extra set of
130+
parentheses surrounding the auxiliary function calls:
131+
<programlisting>
132+
ereport(ERROR,
133+
(errcode(ERRCODE_DIVISION_BY_ZERO),
134+
errmsg("division by zero")));
135+
</programlisting>
136+
The extra parentheses were required
137+
before <productname>PostgreSQL</productname> version 12, but are now
138+
optional.
128139
</para>
129140

130141
<para>
131142
Here is a more complex example:
132143
<programlisting>
133144
ereport(ERROR,
134-
(errcode(ERRCODE_AMBIGUOUS_FUNCTION),
135-
errmsg("function %s is not unique",
136-
func_signature_string(funcname, nargs,
137-
NIL, actual_arg_types)),
138-
errhint("Unable to choose a best candidate function. "
139-
"You might need to add explicit typecasts.")));
145+
errcode(ERRCODE_AMBIGUOUS_FUNCTION),
146+
errmsg("function %s is not unique",
147+
func_signature_string(funcname, nargs,
148+
NIL, actual_arg_types)),
149+
errhint("Unable to choose a best candidate function. "
150+
"You might need to add explicit typecasts."));
140151
</programlisting>
141152
This illustrates the use of format codes to embed run-time values into
142153
a message text. Also, an optional <quote>hint</quote> message is provided.
154+
The auxiliary function calls can be written in any order, but
155+
conventionally <function>errcode</function>
156+
and <function>errmsg</function> appear first.
143157
</para>
144158

145159
<para>
146160
If the severity level is <literal>ERROR</literal> or higher,
147-
<function>ereport</function> abortstheexecution of theuser-defined
148-
functionand does not return to the caller. If the severity level is
161+
<function>ereport</function> aborts execution of thecurrent query
162+
and does not return to the caller. If the severity level is
149163
lower than <literal>ERROR</literal>, <function>ereport</function> returns normally.
150164
</para>
151165

@@ -390,7 +404,7 @@ elog(level, "format string", ...);
390404
</programlisting>
391405
is exactly equivalent to:
392406
<programlisting>
393-
ereport(level,(errmsg_internal("format string", ...)));
407+
ereport(level, errmsg_internal("format string", ...));
394408
</programlisting>
395409
Notice that the SQLSTATE error code is always defaulted, and the message
396410
string is not subject to translation.

‎src/backend/tcop/postgres.c

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -3720,15 +3720,15 @@ process_postgres_switches(int argc, char *argv[], GucContext ctx,
37203720
/* spell the error message a bit differently depending on context */
37213721
if (IsUnderPostmaster)
37223722
ereport(FATAL,
3723-
(errcode(ERRCODE_SYNTAX_ERROR),
3724-
errmsg("invalid command-line argument for server process: %s",argv[optind]),
3725-
errhint("Try \"%s --help\" for more information.",progname)));
3723+
errcode(ERRCODE_SYNTAX_ERROR),
3724+
errmsg("invalid command-line argument for server process: %s",argv[optind]),
3725+
errhint("Try \"%s --help\" for more information.",progname));
37263726
else
37273727
ereport(FATAL,
3728-
(errcode(ERRCODE_SYNTAX_ERROR),
3729-
errmsg("%s: invalid command-line argument: %s",
3730-
progname,argv[optind]),
3731-
errhint("Try \"%s --help\" for more information.",progname)));
3728+
errcode(ERRCODE_SYNTAX_ERROR),
3729+
errmsg("%s: invalid command-line argument: %s",
3730+
progname,argv[optind]),
3731+
errhint("Try \"%s --help\" for more information.",progname));
37323732
}
37333733

37343734
/*

‎src/backend/utils/error/elog.c

Lines changed: 0 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1116,16 +1116,6 @@ errcontext_msg(const char *fmt,...)
11161116
* translate it. Instead, each errcontext_msg() call should be preceded by
11171117
* a set_errcontext_domain() call to specify the domain. This is usually
11181118
* done transparently by the errcontext() macro.
1119-
*
1120-
* Although errcontext is primarily meant for use at call sites distant from
1121-
* the original ereport call, there are a few places that invoke errcontext
1122-
* within ereport. The expansion of errcontext as a comma expression calling
1123-
* set_errcontext_domain then errcontext_msg is problematic in this case,
1124-
* because the intended comma expression becomes two arguments to errfinish,
1125-
* which the compiler is at liberty to evaluate in either order. But in
1126-
* such a case, the set_errcontext_domain calls must be selecting the same
1127-
* TEXTDOMAIN value that the errstart call did, so order does not matter
1128-
* so long as errstart initializes context_domain along with domain.
11291119
*/
11301120
int
11311121
set_errcontext_domain(constchar*domain)

‎src/include/utils/elog.h

Lines changed: 12 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -91,16 +91,19 @@
9191
/*----------
9292
* New-style error reporting API: to be used in this way:
9393
*ereport(ERROR,
94-
*(errcode(ERRCODE_UNDEFINED_CURSOR),
95-
*errmsg("portal \"%s\" not found", stmt->portalname),
96-
*... other errxxx() fields as needed ...));
94+
*errcode(ERRCODE_UNDEFINED_CURSOR),
95+
*errmsg("portal \"%s\" not found", stmt->portalname),
96+
*... other errxxx() fields as needed ...);
9797
*
9898
* The error level is required, and so is a primary error message (errmsg
9999
* or errmsg_internal). All else is optional. errcode() defaults to
100100
* ERRCODE_INTERNAL_ERROR if elevel is ERROR or more, ERRCODE_WARNING
101101
* if elevel is WARNING, or ERRCODE_SUCCESSFUL_COMPLETION if elevel is
102102
* NOTICE or below.
103103
*
104+
* Before Postgres v12, extra parentheses were required around the
105+
* list of auxiliary function calls; that's now optional.
106+
*
104107
* ereport_domain() allows a message domain to be specified, for modules that
105108
* wish to use a different message catalog from the backend's. To avoid having
106109
* one copy of the default text domain per .o file, we define it as NULL here
@@ -118,28 +121,28 @@
118121
*----------
119122
*/
120123
#ifdefHAVE__BUILTIN_CONSTANT_P
121-
#defineereport_domain(elevel,domain,rest)\
124+
#defineereport_domain(elevel,domain,...)\
122125
do { \
123126
pg_prevent_errno_in_scope(); \
124127
if (errstart(elevel, __FILE__, __LINE__, PG_FUNCNAME_MACRO, domain)) \
125-
errfinish rest; \
128+
__VA_ARGS__, errfinish(0); \
126129
if (__builtin_constant_p(elevel) && (elevel) >= ERROR) \
127130
pg_unreachable(); \
128131
} while(0)
129132
#else/* !HAVE__BUILTIN_CONSTANT_P */
130-
#defineereport_domain(elevel,domain,rest)\
133+
#defineereport_domain(elevel,domain,...)\
131134
do { \
132135
const int elevel_ = (elevel); \
133136
pg_prevent_errno_in_scope(); \
134137
if (errstart(elevel_, __FILE__, __LINE__, PG_FUNCNAME_MACRO, domain)) \
135-
errfinish rest; \
138+
__VA_ARGS__, errfinish(0); \
136139
if (elevel_ >= ERROR) \
137140
pg_unreachable(); \
138141
} while(0)
139142
#endif/* HAVE__BUILTIN_CONSTANT_P */
140143

141-
#defineereport(elevel,rest)\
142-
ereport_domain(elevel, TEXTDOMAIN,rest)
144+
#defineereport(elevel,...)\
145+
ereport_domain(elevel, TEXTDOMAIN,__VA_ARGS__)
143146

144147
#defineTEXTDOMAIN NULL
145148

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