Add to_regtypemod function to extract typemod from a string type name.

In combination with to_regtype, this allows converting a string to
the "canonicalized" form emitted by format_type.  That usage requires
parsing the string twice, which is slightly annoying but not really
too expensive.  We considered alternatives such as returning a record
type, but that way was notationally uglier than this, and possibly
less flexible.

Like to_regtype(), we'd rather that this return NULL for any bad
input, but the underlying type-parsing logic isn't yet capable of
not throwing syntax errors.  Adjust the documentation for both
functions to point that out.

In passing, fix up a couple of nearby entries in the System Catalog
Information Functions table that had not gotten the word about our
since-v13 convention for displaying function usage examples.

David Wheeler and Erik Wienhold, reviewed by Pavel Stehule, Jim Jones,
and others.

Discussion: https://postgr.es/m/DF2324CA-2673-4ABE-B382-26B5770B6AA3@justatheory.com

2 files changed, 45 insertions, 0 deletions

diff --git a/src/test/regress/expected/regproc.out b/src/test/regress/expected/regproc.out
index a9420850b87..97b917502ca 100644
--- a/src/test/regress/expected/regproc.out
+++ b/src/test/regress/expected/regproc.out
@@ -447,6 +447,43 @@ SELECT to_regnamespace('foo.bar');
  
 (1 row)
 
+-- Test to_regtypemod
+SELECT to_regtypemod('text');
+ to_regtypemod 
+---------------
+            -1
+(1 row)
+
+SELECT to_regtypemod('timestamp(4)');
+ to_regtypemod 
+---------------
+             4
+(1 row)
+
+SELECT to_regtypemod('no_such_type(4)');
+ to_regtypemod 
+---------------
+              
+(1 row)
+
+SELECT format_type(to_regtype('varchar(32)'), to_regtypemod('varchar(32)'));
+      format_type      
+-----------------------
+ character varying(32)
+(1 row)
+
+SELECT format_type(to_regtype('bit'), to_regtypemod('bit'));
+ format_type 
+-------------
+ bit(1)
+(1 row)
+
+SELECT format_type(to_regtype('"bit"'), to_regtypemod('"bit"'));
+ format_type 
+-------------
+ "bit"
+(1 row)
+
 -- Test soft-error API
 SELECT * FROM pg_input_error_info('ng_catalog.pg_class', 'regclass');
                     message                    | detail | hint | sql_error_code 
diff --git a/src/test/regress/sql/regproc.sql b/src/test/regress/sql/regproc.sql
index de2aa881a8d..232289ac398 100644
--- a/src/test/regress/sql/regproc.sql
+++ b/src/test/regress/sql/regproc.sql
@@ -123,6 +123,14 @@ SELECT to_regnamespace('Nonexistent');
 SELECT to_regnamespace('"Nonexistent"');
 SELECT to_regnamespace('foo.bar');
 
+-- Test to_regtypemod
+SELECT to_regtypemod('text');
+SELECT to_regtypemod('timestamp(4)');
+SELECT to_regtypemod('no_such_type(4)');
+SELECT format_type(to_regtype('varchar(32)'), to_regtypemod('varchar(32)'));
+SELECT format_type(to_regtype('bit'), to_regtypemod('bit'));
+SELECT format_type(to_regtype('"bit"'), to_regtypemod('"bit"'));
+
 -- Test soft-error API
 
 SELECT * FROM pg_input_error_info('ng_catalog.pg_class', 'regclass');