MDEV-32645 CAST(AS UNSIGNED) fails with --view-protocol

Item_float::neg() did not preserve the "presentation" from "this".
So
  CAST(-1e0 AS UNSIGNED)  -- cast from double to unsigned
changes its meaning to:
  CAST(-1 AS UNSIGNED)  -- cast signed to undigned

Fixing Item_float::neg() to construct the new value for
Item_float::presentation as follows:
- if the old value starts with minus, then the minus is truncated:
  '-2e0' -> '2e0'
- otherwise, minus sign followed by its old value:
  '1e0'  -> '-1e0'

mysql-test/main/cast.test

@@ -768,14 +768,11 @@ INSERT INTO t1 VALUES (-1.0);
 SELECT * FROM t1;
 DROP TABLE t1;
 
-#enable after MDEV-32645 is fixed
---disable_view_protocol
 SELECT CAST(-1e0 AS UNSIGNED);
 CREATE TABLE t1 (a BIGINT UNSIGNED);
 INSERT INTO t1 VALUES (-1e0);
 SELECT * FROM t1;
 DROP TABLE t1;
---enable_view_protocol
 
 SELECT CAST(-1e308 AS UNSIGNED);
 CREATE TABLE t1 (a BIGINT UNSIGNED);

mysql-test/main/type_float.result

@@ -1167,5 +1167,42 @@ d	50
 fdbl	123.456.789,12345678000000000000000000000000000000
 fdec	123.456.789,12345678900000000000000000000000000000
 #
+# MDEV-32645 CAST(AS UNSIGNED) fails with --view-protocol
+#
+SELECT
+CAST(-1e0 AS UNSIGNED),
+CAST(--2e0 AS UNSIGNED),
+CAST(---3e0 AS UNSIGNED),
+CAST(----4e0 AS UNSIGNED);
+CAST(-1e0 AS UNSIGNED)	CAST(--2e0 AS UNSIGNED)	CAST(---3e0 AS UNSIGNED)	CAST(----4e0 AS UNSIGNED)
+0	2	0	4
+Warnings:
+Note	1916	Got overflow when converting '-1' to UNSIGNED BIGINT. Value truncated
+Note	1916	Got overflow when converting '-3' to UNSIGNED BIGINT. Value truncated
+EXPLAIN EXTENDED SELECT
+CAST(-1e0 AS UNSIGNED),
+CAST(--2e0 AS UNSIGNED),
+CAST(---3e0 AS UNSIGNED),
+CAST(----4e0 AS UNSIGNED);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1003	select cast(-1e0 as unsigned) AS `CAST(-1e0 AS UNSIGNED)`,cast(2e0 as unsigned) AS `CAST(--2e0 AS UNSIGNED)`,cast(-3e0 as unsigned) AS `CAST(---3e0 AS UNSIGNED)`,cast(4e0 as unsigned) AS `CAST(----4e0 AS UNSIGNED)`
+CREATE VIEW v1 AS SELECT
+CAST(-1e0 AS UNSIGNED),
+CAST(--2e0 AS UNSIGNED),
+CAST(---3e0 AS UNSIGNED),
+CAST(----4e0 AS UNSIGNED);
+SHOW CREATE VIEW v1;
+View	Create View	character_set_client	collation_connection
+v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS select cast(-1e0 as unsigned) AS `CAST(-1e0 AS UNSIGNED)`,cast(2e0 as unsigned) AS `CAST(--2e0 AS UNSIGNED)`,cast(-3e0 as unsigned) AS `CAST(---3e0 AS UNSIGNED)`,cast(4e0 as unsigned) AS `CAST(----4e0 AS UNSIGNED)`	latin1	latin1_swedish_ci
+SELECT * FROM v1;
+CAST(-1e0 AS UNSIGNED)	CAST(--2e0 AS UNSIGNED)	CAST(---3e0 AS UNSIGNED)	CAST(----4e0 AS UNSIGNED)
+0	2	0	4
+Warnings:
+Note	1916	Got overflow when converting '-1' to UNSIGNED BIGINT. Value truncated
+Note	1916	Got overflow when converting '-3' to UNSIGNED BIGINT. Value truncated
+DROP VIEW v1;
+#
 # End of 10.4 tests
 #

mysql-test/main/type_float.test

@@ -713,6 +713,32 @@ $$
 DELIMITER ;$$
 --horizontal_results
 
+--echo #
+--echo # MDEV-32645 CAST(AS UNSIGNED) fails with --view-protocol
+--echo #
+
+SELECT
+  CAST(-1e0 AS UNSIGNED),
+  CAST(--2e0 AS UNSIGNED),
+  CAST(---3e0 AS UNSIGNED),
+  CAST(----4e0 AS UNSIGNED);
+
+EXPLAIN EXTENDED SELECT
+  CAST(-1e0 AS UNSIGNED),
+  CAST(--2e0 AS UNSIGNED),
+  CAST(---3e0 AS UNSIGNED),
+  CAST(----4e0 AS UNSIGNED);
+
+CREATE VIEW v1 AS SELECT
+  CAST(-1e0 AS UNSIGNED),
+  CAST(--2e0 AS UNSIGNED),
+  CAST(---3e0 AS UNSIGNED),
+  CAST(----4e0 AS UNSIGNED);
+
+SHOW CREATE VIEW v1;
+SELECT * FROM v1;
+DROP VIEW v1;
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

sql/item.cc

@@ -6896,7 +6896,25 @@ Item *Item_float::neg(THD *thd)
   else if (value < 0 && max_length)
     max_length--;
   value= -value;
-  presentation= 0;
+  if (presentation)
+  {
+    if (*presentation == '-')
+    {
+      // Strip double minus: -(-1) -> '1' instead of '--1'
+      presentation++;
+    }
+    else
+    {
+      size_t presentation_length= strlen(presentation);
+      if (char *tmp= (char*) thd->alloc(presentation_length + 2))
+      {
+        tmp[0]= '-';
+        // Copy with the trailing '\0'
+        memcpy(tmp + 1, presentation, presentation_length + 1);
+        presentation= tmp;
+      }
+    }
+  }
   name= null_clex_str;
   return this;
 }