Remove dead encoding-conversion functions.

The code for conversions SQL_ASCII <-> MULE_INTERNAL and
SQL_ASCII <-> UTF8 was unreachable, because we long ago changed
the wrapper functions pg_do_encoding_conversion() et al so that
they have hard-wired behaviors for conversions involving SQL_ASCII.
(At least some of those fast paths date back to 2002, though it
looks like we may not have been totally consistent about this until
later.)  Given the lack of complaints, nobody is dissatisfied with
this state of affairs.  Hence, let's just remove the unreachable code.

Also, change CREATE CONVERSION so that it rejects attempts to
define such conversions.  Since we consider that SQL_ASCII represents
lack of knowledge about the encoding in use, such a conversion would
be semantically dubious even if it were reachable.

Adjust a couple of regression test cases that had randomly decided
to rely on these conversion functions rather than any other ones.

Discussion: https://postgr.es/m/41163.1559156593@sss.pgh.pa.us

doc/src/sgml/charset.sgml

@@ -1896,7 +1896,11 @@ RESET client_encoding;
     <para>
      If the client character set is defined as <literal>SQL_ASCII</literal>,
      encoding conversion is disabled, regardless of the server's character
-     set.  Just as for the server, use of <literal>SQL_ASCII</literal> is unwise
+     set.  (However, if the server's character set is
+     not <literal>SQL_ASCII</literal>, the server will still check that
+     incoming data is valid for that encoding; so the net effect is as
+     though the client character set were the same as the server's.)
+     Just as for the server, use of <literal>SQL_ASCII</literal> is unwise
      unless you are working with all-ASCII data.
     </para>
    </sect2>

doc/src/sgml/func.sgml

@@ -2496,18 +2496,6 @@
      </thead>
 
      <tbody>
-      <row>
-       <entry><literal>ascii_to_mic</literal></entry>
-       <entry><literal>SQL_ASCII</literal></entry>
-       <entry><literal>MULE_INTERNAL</literal></entry>
-      </row>
-
-      <row>
-       <entry><literal>ascii_to_utf8</literal></entry>
-       <entry><literal>SQL_ASCII</literal></entry>
-       <entry><literal>UTF8</literal></entry>
-      </row>
-
       <row>
        <entry><literal>big5_to_euc_tw</literal></entry>
        <entry><literal>BIG5</literal></entry>
@@ -2778,12 +2766,6 @@
        <entry><literal>UTF8</literal></entry>
       </row>
 
-      <row>
-       <entry><literal>mic_to_ascii</literal></entry>
-       <entry><literal>MULE_INTERNAL</literal></entry>
-       <entry><literal>SQL_ASCII</literal></entry>
-      </row>
-
       <row>
        <entry><literal>mic_to_big5</literal></entry>
        <entry><literal>MULE_INTERNAL</literal></entry>
@@ -2904,12 +2886,6 @@
        <entry><literal>UTF8</literal></entry>
       </row>
 
-      <row>
-       <entry><literal>utf8_to_ascii</literal></entry>
-       <entry><literal>UTF8</literal></entry>
-       <entry><literal>SQL_ASCII</literal></entry>
-      </row>
-
       <row>
        <entry><literal>utf8_to_big5</literal></entry>
        <entry><literal>UTF8</literal></entry>

doc/src/sgml/ref/create_conversion.sgml

@@ -28,12 +28,15 @@ CREATE [ DEFAULT ] CONVERSION <replaceable>name</replaceable>
 
   <para>
    <command>CREATE CONVERSION</command> defines a new conversion between
-   character set encodings.  Also, conversions that
-   are marked <literal>DEFAULT</literal> can be used for automatic encoding
-   conversion between
-   client and server. For this purpose, two conversions, from encoding A to
-   B <emphasis>and</emphasis> from encoding B to A, must be defined.
- </para>
+   two character set encodings.
+  </para>
+
+  <para>
+   Conversions that are marked <literal>DEFAULT</literal> can be used for
+   automatic encoding conversion between client and server.  To support that
+   usage, two conversions, from encoding A to B <emphasis>and</emphasis>
+   from encoding B to A, must be defined.
+  </para>
 
   <para>
    To be able to create a conversion, you must have <literal>EXECUTE</literal> privilege
@@ -122,6 +125,13 @@ conv_proc(
  <refsect1 id="sql-createconversion-notes">
   <title>Notes</title>
 
+  <para>
+   Neither the source nor the destination encoding can
+   be <literal>SQL_ASCII</literal>, as the server's behavior for cases
+   involving the <literal>SQL_ASCII</literal> <quote>encoding</quote> is
+   hard-wired.
+  </para>
+
   <para>
    Use <command>DROP CONVERSION</command> to remove user-defined conversions.
   </para>

src/backend/commands/conversioncmds.c

@@ -72,6 +72,18 @@ CreateConversionCommand(CreateConversionStmt *stmt)
 				 errmsg("destination encoding \"%s\" does not exist",
 						to_encoding_name)));
 
+	/*
+	 * We consider conversions to or from SQL_ASCII to be meaningless.  (If
+	 * you wish to change this, note that pg_do_encoding_conversion() and its
+	 * sister functions have hard-wired fast paths for any conversion in which
+	 * the source or target encoding is SQL_ASCII, so that an encoding
+	 * conversion function declared for such a case will never be used.)
+	 */
+	if (from_encoding == PG_SQL_ASCII || to_encoding == PG_SQL_ASCII)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("encoding conversion to or from \"SQL_ASCII\" is not supported")));
+
 	/*
 	 * Check the existence of the conversion function. Function name could be
 	 * a qualified name.

src/backend/utils/mb/conv.c

@@ -132,51 +132,6 @@ mic2latin(const unsigned char *mic, unsigned char *p, int len,
 }
 
 
-/*
- * ASCII ---> MIC
- *
- * While ordinarily SQL_ASCII encoding is forgiving of high-bit-set
- * characters, here we must take a hard line because we don't know
- * the appropriate MIC equivalent.
- */
-void
-pg_ascii2mic(const unsigned char *l, unsigned char *p, int len)
-{
-	int			c1;
-
-	while (len > 0)
-	{
-		c1 = *l;
-		if (c1 == 0 || IS_HIGHBIT_SET(c1))
-			report_invalid_encoding(PG_SQL_ASCII, (const char *) l, len);
-		*p++ = c1;
-		l++;
-		len--;
-	}
-	*p = '\0';
-}
-
-/*
- * MIC ---> ASCII
- */
-void
-pg_mic2ascii(const unsigned char *mic, unsigned char *p, int len)
-{
-	int			c1;
-
-	while (len > 0)
-	{
-		c1 = *mic;
-		if (c1 == 0 || IS_HIGHBIT_SET(c1))
-			report_untranslatable_char(PG_MULE_INTERNAL, PG_SQL_ASCII,
-									   (const char *) mic, len);
-		*p++ = c1;
-		mic++;
-		len--;
-	}
-	*p = '\0';
-}
-
 /*
  * latin2mic_with_table: a generic single byte charset encoding
  * conversion from a local charset to the mule internal code.

src/backend/utils/mb/conversion_procs/Makefile

@@ -14,9 +14,9 @@ top_builddir = ../../../../..
 include $(top_builddir)/src/Makefile.global
 
 SUBDIRS = \
-	ascii_and_mic cyrillic_and_mic euc_cn_and_mic euc_jp_and_sjis \
+	cyrillic_and_mic euc_cn_and_mic euc_jp_and_sjis \
 	euc_kr_and_mic euc_tw_and_big5 latin2_and_win1250 latin_and_mic \
-	utf8_and_ascii utf8_and_big5 utf8_and_cyrillic utf8_and_euc_cn \
+	utf8_and_big5 utf8_and_cyrillic utf8_and_euc_cn \
 	utf8_and_euc_jp utf8_and_euc_kr utf8_and_euc_tw utf8_and_gb18030 \
 	utf8_and_gbk utf8_and_iso8859 utf8_and_iso8859_1 utf8_and_johab \
 	utf8_and_sjis utf8_and_win utf8_and_uhc \

src/backend/utils/mb/conversion_procs/ascii_and_mic/Makefile

-#-------------------------------------------------------------------------
-#
-# src/backend/utils/mb/conversion_procs/ascii_and_mic/Makefile
-#
-#-------------------------------------------------------------------------
-subdir = src/backend/utils/mb/conversion_procs/ascii_and_mic
-top_builddir = ../../../../../..
-include $(top_builddir)/src/Makefile.global
-
-NAME		= ascii_and_mic
-PGFILEDESC	= "ascii <-> mic text conversions"
-
-include $(srcdir)/../proc.mk

src/backend/utils/mb/conversion_procs/ascii_and_mic/ascii_and_mic.c

-/*-------------------------------------------------------------------------
- *
- *	  ASCII and MULE_INTERNAL
- *
- * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * IDENTIFICATION
- *	  src/backend/utils/mb/conversion_procs/ascii_and_mic/ascii_and_mic.c
- *
- *-------------------------------------------------------------------------
- */
-
-#include "postgres.h"
-#include "fmgr.h"
-#include "mb/pg_wchar.h"
-
-PG_MODULE_MAGIC;
-
-PG_FUNCTION_INFO_V1(ascii_to_mic);
-PG_FUNCTION_INFO_V1(mic_to_ascii);
-
-/* ----------
- * conv_proc(
- *		INTEGER,	-- source encoding id
- *		INTEGER,	-- destination encoding id
- *		CSTRING,	-- source string (null terminated C string)
- *		CSTRING,	-- destination string (null terminated C string)
- *		INTEGER		-- source string length
- * ) returns VOID;
- * ----------
- */
-
-Datum
-ascii_to_mic(PG_FUNCTION_ARGS)
-{
-	unsigned char *src = (unsigned char *) PG_GETARG_CSTRING(2);
-	unsigned char *dest = (unsigned char *) PG_GETARG_CSTRING(3);
-	int			len = PG_GETARG_INT32(4);
-
-	CHECK_ENCODING_CONVERSION_ARGS(PG_SQL_ASCII, PG_MULE_INTERNAL);
-
-	pg_ascii2mic(src, dest, len);
-
-	PG_RETURN_VOID();
-}
-
-Datum
-mic_to_ascii(PG_FUNCTION_ARGS)
-{
-	unsigned char *src = (unsigned char *) PG_GETARG_CSTRING(2);
-	unsigned char *dest = (unsigned char *) PG_GETARG_CSTRING(3);
-	int			len = PG_GETARG_INT32(4);
-
-	CHECK_ENCODING_CONVERSION_ARGS(PG_MULE_INTERNAL, PG_SQL_ASCII);
-
-	pg_mic2ascii(src, dest, len);
-
-	PG_RETURN_VOID();
-}

src/backend/utils/mb/conversion_procs/utf8_and_ascii/Makefile

-#-------------------------------------------------------------------------
-#
-# src/backend/utils/mb/conversion_procs/utf8_and_ascii/Makefile
-#
-#-------------------------------------------------------------------------
-subdir = src/backend/utils/mb/conversion_procs/utf8_and_ascii
-top_builddir = ../../../../../..
-include $(top_builddir)/src/Makefile.global
-
-NAME		= utf8_and_ascii
-PGFILEDESC	= "utf8 <-> ascii text conversions"
-
-include $(srcdir)/../proc.mk

src/backend/utils/mb/conversion_procs/utf8_and_ascii/utf8_and_ascii.c

-/*-------------------------------------------------------------------------
- *
- *	  ASCII <--> UTF8
- *
- * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * IDENTIFICATION
- *	  src/backend/utils/mb/conversion_procs/utf8_and_ascii/utf8_and_ascii.c
- *
- *-------------------------------------------------------------------------
- */
-
-#include "postgres.h"
-#include "fmgr.h"
-#include "mb/pg_wchar.h"
-
-PG_MODULE_MAGIC;
-
-PG_FUNCTION_INFO_V1(ascii_to_utf8);
-PG_FUNCTION_INFO_V1(utf8_to_ascii);
-
-/* ----------
- * conv_proc(
- *		INTEGER,	-- source encoding id
- *		INTEGER,	-- destination encoding id
- *		CSTRING,	-- source string (null terminated C string)
- *		CSTRING,	-- destination string (null terminated C string)
- *		INTEGER		-- source string length
- * ) returns VOID;
- * ----------
- */
-
-Datum
-ascii_to_utf8(PG_FUNCTION_ARGS)
-{
-	unsigned char *src = (unsigned char *) PG_GETARG_CSTRING(2);
-	unsigned char *dest = (unsigned char *) PG_GETARG_CSTRING(3);
-	int			len = PG_GETARG_INT32(4);
-
-	CHECK_ENCODING_CONVERSION_ARGS(PG_SQL_ASCII, PG_UTF8);
-
-	/* this looks wrong, but basically we're just rejecting high-bit-set */
-	pg_ascii2mic(src, dest, len);
-
-	PG_RETURN_VOID();
-}
-
-Datum
-utf8_to_ascii(PG_FUNCTION_ARGS)
-{
-	unsigned char *src = (unsigned char *) PG_GETARG_CSTRING(2);
-	unsigned char *dest = (unsigned char *) PG_GETARG_CSTRING(3);
-	int			len = PG_GETARG_INT32(4);
-
-	CHECK_ENCODING_CONVERSION_ARGS(PG_UTF8, PG_SQL_ASCII);
-
-	/* this looks wrong, but basically we're just rejecting high-bit-set */
-	pg_mic2ascii(src, dest, len);
-
-	PG_RETURN_VOID();
-}

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201907053
+#define CATALOG_VERSION_NO	201907054
 
 #endif

src/include/catalog/pg_conversion.dat

@@ -15,12 +15,6 @@
 
 [
 
-{ oid => '4400', descr => 'conversion for SQL_ASCII to MULE_INTERNAL',
-  conname => 'ascii_to_mic', conforencoding => 'PG_SQL_ASCII',
-  contoencoding => 'PG_MULE_INTERNAL', conproc => 'ascii_to_mic' },
-{ oid => '4401', descr => 'conversion for MULE_INTERNAL to SQL_ASCII',
-  conname => 'mic_to_ascii', conforencoding => 'PG_MULE_INTERNAL',
-  contoencoding => 'PG_SQL_ASCII', conproc => 'mic_to_ascii' },
 { oid => '4402', descr => 'conversion for KOI8R to MULE_INTERNAL',
   conname => 'koi8_r_to_mic', conforencoding => 'PG_KOI8R',
   contoencoding => 'PG_MULE_INTERNAL', conproc => 'koi8r_to_mic' },
@@ -165,12 +159,6 @@
 { oid => '4449', descr => 'conversion for MULE_INTERNAL to LATIN4',
   conname => 'mic_to_iso_8859_4', conforencoding => 'PG_MULE_INTERNAL',
   contoencoding => 'PG_LATIN4', conproc => 'mic_to_latin4' },
-{ oid => '4450', descr => 'conversion for SQL_ASCII to UTF8',
-  conname => 'ascii_to_utf8', conforencoding => 'PG_SQL_ASCII',
-  contoencoding => 'PG_UTF8', conproc => 'ascii_to_utf8' },
-{ oid => '4451', descr => 'conversion for UTF8 to SQL_ASCII',
-  conname => 'utf8_to_ascii', conforencoding => 'PG_UTF8',
-  contoencoding => 'PG_SQL_ASCII', conproc => 'utf8_to_ascii' },
 { oid => '4452', descr => 'conversion for BIG5 to UTF8',
   conname => 'big5_to_utf8', conforencoding => 'PG_BIG5',
   contoencoding => 'PG_UTF8', conproc => 'big5_to_utf8' },

src/include/catalog/pg_proc.dat

@@ -10082,16 +10082,6 @@
   prosrc => 'binary_upgrade_set_missing_value' },
 
 # conversion functions
-{ oid => '4300',
-  descr => 'internal conversion function for SQL_ASCII to MULE_INTERNAL',
-  proname => 'ascii_to_mic', prolang => 'c', prorettype => 'void',
-  proargtypes => 'int4 int4 cstring internal int4', prosrc => 'ascii_to_mic',
-  probin => '$libdir/ascii_and_mic' },
-{ oid => '4301',
-  descr => 'internal conversion function for MULE_INTERNAL to SQL_ASCII',
-  proname => 'mic_to_ascii', prolang => 'c', prorettype => 'void',
-  proargtypes => 'int4 int4 cstring internal int4', prosrc => 'mic_to_ascii',
-  probin => '$libdir/ascii_and_mic' },
 { oid => '4302',
   descr => 'internal conversion function for KOI8R to MULE_INTERNAL',
   proname => 'koi8r_to_mic', prolang => 'c', prorettype => 'void',
@@ -10324,16 +10314,6 @@
   proname => 'mic_to_latin4', prolang => 'c', prorettype => 'void',
   proargtypes => 'int4 int4 cstring internal int4', prosrc => 'mic_to_latin4',
   probin => '$libdir/latin_and_mic' },
-{ oid => '4350',
-  descr => 'internal conversion function for SQL_ASCII to UTF8',
-  proname => 'ascii_to_utf8', prolang => 'c', prorettype => 'void',
-  proargtypes => 'int4 int4 cstring internal int4', prosrc => 'ascii_to_utf8',
-  probin => '$libdir/utf8_and_ascii' },
-{ oid => '4351',
-  descr => 'internal conversion function for UTF8 to SQL_ASCII',
-  proname => 'utf8_to_ascii', prolang => 'c', prorettype => 'void',
-  proargtypes => 'int4 int4 cstring internal int4', prosrc => 'utf8_to_ascii',
-  probin => '$libdir/utf8_and_ascii' },
 { oid => '4352', descr => 'internal conversion function for BIG5 to UTF8',
   proname => 'big5_to_utf8', prolang => 'c', prorettype => 'void',
   proargtypes => 'int4 int4 cstring internal int4', prosrc => 'big5_to_utf8',

src/include/mb/pg_wchar.h

@@ -614,8 +614,6 @@ extern void report_untranslatable_char(int src_encoding, int dest_encoding,
 
 extern void local2local(const unsigned char *l, unsigned char *p, int len,
 						int src_encoding, int dest_encoding, const unsigned char *tab);
-extern void pg_ascii2mic(const unsigned char *l, unsigned char *p, int len);
-extern void pg_mic2ascii(const unsigned char *mic, unsigned char *p, int len);
 extern void latin2mic(const unsigned char *l, unsigned char *p, int len,
 					  int lc, int encoding);
 extern void mic2latin(const unsigned char *mic, unsigned char *p, int len,

src/test/regress/expected/alter_table.out

@@ -2713,7 +2713,7 @@ as 'select $1.f1 is not distinct from $2.f1 and $1.f2 is not distinct from $2.f2
 create operator alter1.=(procedure = alter1.same, leftarg  = alter1.ctype, rightarg = alter1.ctype);
 create operator class alter1.ctype_hash_ops default for type alter1.ctype using hash as
   operator 1 alter1.=(alter1.ctype, alter1.ctype);
-create conversion alter1.ascii_to_utf8 for 'sql_ascii' to 'utf8' from ascii_to_utf8;
+create conversion alter1.latin1_to_utf8 for 'latin1' to 'utf8' from iso8859_1_to_utf8;
 create text search parser alter1.prs(start = prsd_start, gettoken = prsd_nexttoken, end = prsd_end, lextypes = prsd_lextype);
 create text search configuration alter1.cfg(parser = alter1.prs);
 create text search template alter1.tmpl(init = dsimple_init, lexize = dsimple_lexize);
@@ -2731,7 +2731,7 @@ alter operator alter1.=(alter1.ctype, alter1.ctype) set schema alter2;
 alter function alter1.same(alter1.ctype, alter1.ctype) set schema alter2;
 alter type alter1.ctype set schema alter1; -- no-op, same schema
 alter type alter1.ctype set schema alter2;
-alter conversion alter1.ascii_to_utf8 set schema alter2;
+alter conversion alter1.latin1_to_utf8 set schema alter2;
 alter text search parser alter1.prs set schema alter2;
 alter text search configuration alter1.cfg set schema alter2;
 alter text search template alter1.tmpl set schema alter2;
@@ -2775,7 +2775,7 @@ drop cascades to type alter2.ctype
 drop cascades to function alter2.same(alter2.ctype,alter2.ctype)
 drop cascades to operator alter2.=(alter2.ctype,alter2.ctype)
 drop cascades to operator family alter2.ctype_hash_ops for access method hash
-drop cascades to conversion alter2.ascii_to_utf8
+drop cascades to conversion alter2.latin1_to_utf8
 drop cascades to text search parser alter2.prs
 drop cascades to text search configuration alter2.cfg
 drop cascades to text search template alter2.tmpl

src/test/regress/expected/object_address.out

@@ -394,7 +394,7 @@ WITH objects (type, name, args) AS (VALUES
 				('collation', '{default}', '{}'),
 				('table constraint', '{addr_nsp, gentable, a_chk}', '{}'),
 				('domain constraint', '{addr_nsp.gendomain}', '{domconstr}'),
-				('conversion', '{pg_catalog, ascii_to_mic}', '{}'),
+				('conversion', '{pg_catalog, koi8_r_to_mic}', '{}'),
 				('default value', '{addr_nsp, gentable, b}', '{}'),
 				('language', '{plpgsql}', '{}'),
 				-- large object
@@ -468,7 +468,7 @@ SELECT (pg_identify_object(addr1.classid, addr1.objid, addr1.objsubid)).*,
  cast                      |            |                   | (bigint AS integer)                                                  | t
  table constraint          | addr_nsp   |                   | a_chk on addr_nsp.gentable                                           | t
  domain constraint         | addr_nsp   |                   | domconstr on addr_nsp.gendomain                                      | t
- conversion                | pg_catalog | ascii_to_mic      | pg_catalog.ascii_to_mic                                              | t
+ conversion                | pg_catalog | koi8_r_to_mic     | pg_catalog.koi8_r_to_mic                                             | t
  language                  |            | plpgsql           | plpgsql                                                              | t
  schema                    |            | addr_nsp          | addr_nsp                                                             | t
  operator class            | pg_catalog | int4_ops          | pg_catalog.int4_ops USING btree                                      | t

src/test/regress/sql/alter_table.sql

@@ -1735,7 +1735,7 @@ create operator alter1.=(procedure = alter1.same, leftarg  = alter1.ctype, right
 create operator class alter1.ctype_hash_ops default for type alter1.ctype using hash as
   operator 1 alter1.=(alter1.ctype, alter1.ctype);
 
-create conversion alter1.ascii_to_utf8 for 'sql_ascii' to 'utf8' from ascii_to_utf8;
+create conversion alter1.latin1_to_utf8 for 'latin1' to 'utf8' from iso8859_1_to_utf8;
 
 create text search parser alter1.prs(start = prsd_start, gettoken = prsd_nexttoken, end = prsd_end, lextypes = prsd_lextype);
 create text search configuration alter1.cfg(parser = alter1.prs);
@@ -1756,7 +1756,7 @@ alter operator alter1.=(alter1.ctype, alter1.ctype) set schema alter2;
 alter function alter1.same(alter1.ctype, alter1.ctype) set schema alter2;
 alter type alter1.ctype set schema alter1; -- no-op, same schema
 alter type alter1.ctype set schema alter2;
-alter conversion alter1.ascii_to_utf8 set schema alter2;
+alter conversion alter1.latin1_to_utf8 set schema alter2;
 alter text search parser alter1.prs set schema alter2;
 alter text search configuration alter1.cfg set schema alter2;
 alter text search template alter1.tmpl set schema alter2;

src/test/regress/sql/object_address.sql

@@ -164,7 +164,7 @@ WITH objects (type, name, args) AS (VALUES
 				('collation', '{default}', '{}'),
 				('table constraint', '{addr_nsp, gentable, a_chk}', '{}'),
 				('domain constraint', '{addr_nsp.gendomain}', '{domconstr}'),
-				('conversion', '{pg_catalog, ascii_to_mic}', '{}'),
+				('conversion', '{pg_catalog, koi8_r_to_mic}', '{}'),
 				('default value', '{addr_nsp, gentable, b}', '{}'),
 				('language', '{plpgsql}', '{}'),
 				-- large object