Add test scaffolding for soft error reporting from input functions.

pg_input_is_valid() returns boolean, while pg_input_error_message()
returns the primary error message if the input is bad, or NULL
if the input is OK.  The main reason for having two functions is
so that we can test both the details-wanted and the no-details-wanted
code paths.

Although these are primarily designed with testing in mind,
it could well be that they'll be useful to end users as well.

This patch is mostly by me, but it owes very substantial debt to
earlier work by Nikita Glukhov, Andrew Dunstan, and Amul Sul.
Thanks to Andres Freund for review.

Discussion: https://postgr.es/m/3bbbb0df-7382-bf87-9737-340ba096e034@postgrespro.ru

doc/src/sgml/func.sgml

@@ -24683,6 +24683,107 @@ SELECT collation for ('foo' COLLATE "de_DE");
 
   </sect2>
 
+  <sect2 id="functions-info-validity">
+   <title>Data Validity Checking Functions</title>
+
+   <para>
+    The functions shown in <xref linkend="functions-info-validity-table"/>
+    can be helpful for checking validity of proposed input data.
+   </para>
+
+   <table id="functions-info-validity-table">
+    <title>Data Validity Checking Functions</title>
+    <tgroup cols="1">
+     <thead>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        Function
+       </para>
+       <para>
+        Description
+       </para>
+       <para>
+        Example(s)
+       </para></entry>
+      </row>
+     </thead>
+
+     <tbody>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_input_is_valid</primary>
+        </indexterm>
+        <function>pg_input_is_valid</function> (
+          <parameter>string</parameter> <type>text</type>,
+          <parameter>type</parameter> <type>text</type>
+        )
+        <returnvalue>boolean</returnvalue>
+       </para>
+       <para>
+        Tests whether the given <parameter>string</parameter> is valid
+        input for the specified data type, returning true or false.
+       </para>
+       <para>
+        This function will only work as desired if the data type's input
+        function has been updated to report invalid input as
+        a <quote>soft</quote> error.  Otherwise, invalid input will abort
+        the transaction, just as if the string had been cast to the type
+        directly.
+        </para>
+        <para>
+         <literal>pg_input_is_valid('42', 'integer')</literal>
+         <returnvalue>t</returnvalue>
+        </para>
+        <para>
+         <literal>pg_input_is_valid('42000000000', 'integer')</literal>
+         <returnvalue>f</returnvalue>
+        </para>
+        <para>
+         <literal>pg_input_is_valid('1234.567', 'numeric(7,4)')</literal>
+         <returnvalue>f</returnvalue>
+       </para></entry>
+      </row>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_input_error_message</primary>
+        </indexterm>
+        <function>pg_input_error_message</function> (
+          <parameter>string</parameter> <type>text</type>,
+          <parameter>type</parameter> <type>text</type>
+        )
+        <returnvalue>text</returnvalue>
+       </para>
+       <para>
+        Tests whether the given <parameter>string</parameter> is valid
+        input for the specified data type; if not, return the error
+        message that would have been thrown.  If the input is valid, the
+        result is NULL.  The inputs are the same as
+        for <function>pg_input_is_valid</function>.
+       </para>
+       <para>
+        This function will only work as desired if the data type's input
+        function has been updated to report invalid input as
+        a <quote>soft</quote> error.  Otherwise, invalid input will abort
+        the transaction, just as if the string had been cast to the type
+        directly.
+        </para>
+        <para>
+         <literal>pg_input_error_message('42000000000', 'integer')</literal>
+         <returnvalue>value "42000000000" is out of range for type integer</returnvalue>
+        </para>
+        <para>
+         <literal>pg_input_error_message('1234.567', 'numeric(7,4)')</literal>
+         <returnvalue>numeric field overflow</returnvalue>
+       </para></entry>
+      </row>
+     </tbody>
+    </tgroup>
+   </table>
+
+  </sect2>
+
   <sect2 id="functions-info-snapshot">
    <title>Transaction ID and Snapshot Information Functions</title>
 

src/backend/utils/adt/misc.c

@@ -32,6 +32,8 @@
 #include "common/keywords.h"
 #include "funcapi.h"
 #include "miscadmin.h"
+#include "nodes/miscnodes.h"
+#include "parser/parse_type.h"
 #include "parser/scansup.h"
 #include "pgstat.h"
 #include "postmaster/syslogger.h"
@@ -45,6 +47,25 @@
 #include "utils/ruleutils.h"
 #include "utils/timestamp.h"
 
+
+/*
+ * structure to cache metadata needed in pg_input_is_valid_common
+ */
+typedef struct ValidIOData
+{
+	Oid			typoid;
+	int32		typmod;
+	bool		typname_constant;
+	Oid			typiofunc;
+	Oid			typioparam;
+	FmgrInfo	inputproc;
+} ValidIOData;
+
+static bool pg_input_is_valid_common(FunctionCallInfo fcinfo,
+									 text *txt, text *typname,
+									 ErrorSaveContext *escontext);
+
+
 /*
  * Common subroutine for num_nulls() and num_nonnulls().
  * Returns true if successful, false if function should return NULL.
@@ -640,6 +661,114 @@ pg_column_is_updatable(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * pg_input_is_valid - test whether string is valid input for datatype.
+ *
+ * Returns true if OK, false if not.
+ *
+ * This will only work usefully if the datatype's input function has been
+ * updated to return "soft" errors via errsave/ereturn.
+ */
+Datum
+pg_input_is_valid(PG_FUNCTION_ARGS)
+{
+	text	   *txt = PG_GETARG_TEXT_PP(0);
+	text	   *typname = PG_GETARG_TEXT_PP(1);
+	ErrorSaveContext escontext = {T_ErrorSaveContext};
+
+	PG_RETURN_BOOL(pg_input_is_valid_common(fcinfo, txt, typname,
+											&escontext));
+}
+
+/*
+ * pg_input_error_message - test whether string is valid input for datatype.
+ *
+ * Returns NULL if OK, else the primary message string from the error.
+ *
+ * This will only work usefully if the datatype's input function has been
+ * updated to return "soft" errors via errsave/ereturn.
+ */
+Datum
+pg_input_error_message(PG_FUNCTION_ARGS)
+{
+	text	   *txt = PG_GETARG_TEXT_PP(0);
+	text	   *typname = PG_GETARG_TEXT_PP(1);
+	ErrorSaveContext escontext = {T_ErrorSaveContext};
+
+	/* Enable details_wanted */
+	escontext.details_wanted = true;
+
+	if (pg_input_is_valid_common(fcinfo, txt, typname,
+								 &escontext))
+		PG_RETURN_NULL();
+
+	Assert(escontext.error_occurred);
+	Assert(escontext.error_data != NULL);
+	Assert(escontext.error_data->message != NULL);
+
+	PG_RETURN_TEXT_P(cstring_to_text(escontext.error_data->message));
+}
+
+/* Common subroutine for the above */
+static bool
+pg_input_is_valid_common(FunctionCallInfo fcinfo,
+						 text *txt, text *typname,
+						 ErrorSaveContext *escontext)
+{
+	char	   *str = text_to_cstring(txt);
+	ValidIOData *my_extra;
+	Datum		converted;
+
+	/*
+	 * We arrange to look up the needed I/O info just once per series of
+	 * calls, assuming the data type doesn't change underneath us.
+	 */
+	my_extra = (ValidIOData *) fcinfo->flinfo->fn_extra;
+	if (my_extra == NULL)
+	{
+		fcinfo->flinfo->fn_extra =
+			MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
+							   sizeof(ValidIOData));
+		my_extra = (ValidIOData *) fcinfo->flinfo->fn_extra;
+		my_extra->typoid = InvalidOid;
+		/* Detect whether typname argument is constant. */
+		my_extra->typname_constant = get_fn_expr_arg_stable(fcinfo->flinfo, 1);
+	}
+
+	/*
+	 * If the typname argument is constant, we only need to parse it the first
+	 * time through.
+	 */
+	if (my_extra->typoid == InvalidOid || !my_extra->typname_constant)
+	{
+		char	   *typnamestr = text_to_cstring(typname);
+		Oid			typoid;
+
+		/* Parse type-name argument to obtain type OID and encoded typmod. */
+		parseTypeString(typnamestr, &typoid, &my_extra->typmod, false);
+
+		/* Update type-specific info if typoid changed. */
+		if (my_extra->typoid != typoid)
+		{
+			getTypeInputInfo(typoid,
+							 &my_extra->typiofunc,
+							 &my_extra->typioparam);
+			fmgr_info_cxt(my_extra->typiofunc, &my_extra->inputproc,
+						  fcinfo->flinfo->fn_mcxt);
+			my_extra->typoid = typoid;
+		}
+	}
+
+	/* Now we can try to perform the conversion. */
+	return InputFunctionCallSafe(&my_extra->inputproc,
+								 str,
+								 my_extra->typioparam,
+								 my_extra->typmod,
+								 (Node *) escontext,
+								 &converted);
+}
+
+
 /*
  * Is character a valid identifier start?
  * Must match scan.l's {ident_start} character class.

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202212091
+#define CATALOG_VERSION_NO	202212092
 
 #endif

src/include/catalog/pg_proc.dat

@@ -7060,6 +7060,14 @@
   prorettype => 'regnamespace', proargtypes => 'text',
   prosrc => 'to_regnamespace' },
 
+{ oid => '8050', descr => 'test whether string is valid input for data type',
+  proname => 'pg_input_is_valid', provolatile => 's', prorettype => 'bool',
+  proargtypes => 'text text', prosrc => 'pg_input_is_valid' },
+{ oid => '8051',
+  descr => 'get error message if string is not valid input for data type',
+  proname => 'pg_input_error_message', provolatile => 's', prorettype => 'text',
+  proargtypes => 'text text', prosrc => 'pg_input_error_message' },
+
 { oid => '1268',
   descr => 'parse qualified identifier to array of identifiers',
   proname => 'parse_ident', prorettype => '_text', proargtypes => 'text bool',

src/test/regress/expected/create_type.out

@@ -249,6 +249,31 @@ select format_type('bpchar'::regtype, -1);
  bpchar
 (1 row)
 
+-- Test non-error-throwing APIs using widget, which still throws errors
+SELECT pg_input_is_valid('(1,2,3)', 'widget');
+ pg_input_is_valid 
+-------------------
+ t
+(1 row)
+
+SELECT pg_input_is_valid('(1,2)', 'widget');  -- hard error expected
+ERROR:  invalid input syntax for type widget: "(1,2)"
+SELECT pg_input_is_valid('{"(1,2,3)"}', 'widget[]');
+ pg_input_is_valid 
+-------------------
+ t
+(1 row)
+
+SELECT pg_input_is_valid('{"(1,2)"}', 'widget[]');  -- hard error expected
+ERROR:  invalid input syntax for type widget: "(1,2)"
+SELECT pg_input_is_valid('("(1,2,3)")', 'mytab');
+ pg_input_is_valid 
+-------------------
+ t
+(1 row)
+
+SELECT pg_input_is_valid('("(1,2)")', 'mytab');  -- hard error expected
+ERROR:  invalid input syntax for type widget: "(1,2)"
 -- Test creation of an operator over a user-defined type
 CREATE FUNCTION pt_in_widget(point, widget)
    RETURNS bool

src/test/regress/regress.c

@@ -183,6 +183,11 @@ widget_in(PG_FUNCTION_ARGS)
 			coord[i++] = p + 1;
 	}
 
+	/*
+	 * Note: DON'T convert this error to "soft" style (errsave/ereturn).  We
+	 * want this data type to stay permanently in the hard-error world so that
+	 * it can be used for testing that such cases still work reasonably.
+	 */
 	if (i < NARGS)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),

src/test/regress/sql/create_type.sql

@@ -192,6 +192,14 @@ select format_type('bpchar'::regtype, null);
 -- this behavior difference is intentional
 select format_type('bpchar'::regtype, -1);
 
+-- Test non-error-throwing APIs using widget, which still throws errors
+SELECT pg_input_is_valid('(1,2,3)', 'widget');
+SELECT pg_input_is_valid('(1,2)', 'widget');  -- hard error expected
+SELECT pg_input_is_valid('{"(1,2,3)"}', 'widget[]');
+SELECT pg_input_is_valid('{"(1,2)"}', 'widget[]');  -- hard error expected
+SELECT pg_input_is_valid('("(1,2,3)")', 'mytab');
+SELECT pg_input_is_valid('("(1,2)")', 'mytab');  -- hard error expected
+
 -- Test creation of an operator over a user-defined type
 
 CREATE FUNCTION pt_in_widget(point, widget)