Assertion failure with ALTER TABLE ATTACH PARTITION withlog_min_messages >= DEBUG1

Hi all,

Running installcheck on an instance with log_min_messages = DEBUG1, I
can bump into the following assertion failure:
#2  0x000056145231e82c in ExceptionalCondition
(conditionName=0x56145258ae0b "!(strvalue != ((void *)0))",
errorType=0x56145258adfb "FailedAssertion",
    fileName=0x56145258adf0 "snprintf.c", lineNumber=440) at assert.c:54
[...]
#7  0x000056145231f518 in errmsg (fmt=0x5614524dac60 "validating foreign
key constraint \"%s\"") at elog.c:796
#8  0x0000561451f6ab54 in validateForeignKeyConstraint (conname=0x0,
rel=0x7f12833ca750, pkrel=0x7f12833cc468, pkindOid=36449,
constraintOid=36466) at tablecmds.c:8566
#9  0x0000561451f61589 in ATRewriteTables (parsetree=0x561453bde5e0,
wqueue=0x7ffe8f1d55e8, lockmode=8) at tablecmds.c:4549

Looking at the stack trace there is this log in
validateForeignKeyConstraint:
ereport(DEBUG1,
        (errmsg("validating foreign key constraint \"%s\"", conname)));

However conname is set to NULL in this code path.

This test case allows to reproduce easily the failure:
CREATE TABLE fk_notpartitioned_pk (a int, b int, PRIMARY KEY (a, b));
CREATE TABLE fk_partitioned_fk (b int, a int) PARTITION BY RANGE (a, b);
CREATE TABLE fk_partitioned_fk_1 (b int, a int);
ALTER TABLE fk_partitioned_fk ADD FOREIGN KEY (a, b) REFERENCES
fk_notpartitioned_pk;
-- crash
ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_1 FOR
  VALUES FROM (1,1) TO (2,2);

From what I can see the problem comes from CloneForeignKeyConstraint
which forgets to assign the constraint name when cloning the FK
definition.  While looking at the ATTACH PARTITION code, I have noticed
that a variable gets overridden, which is in my opinion bad style.  So
the problem is rather close to what Tom has fixed in 3d0f68dd it seems.

Attached is a patch for all that, with which installcheck-world passes
for me.  I am surprised this was not noticed before, the recent snprintf
stanza is nicely helping, and this would need to be back-patched down to
v11.

Thanks,
--
Michael