Record dependencies of a cast on other casts that it requires.

When creating a cast that uses a conversion function, we've
historically allowed the input and result types to be
binary-compatible with the function's input and result types,
rather than necessarily being identical.  This means that the new
cast is logically dependent on the binary-compatible cast or casts
that it references: if those are defined by pg_cast entries, and you
try to restore the new cast without having defined them, it'll fail.
Hence, we should make pg_depend entries to record these dependencies
so that pg_dump knows that there is an ordering requirement.

This is not the only place where we allow such shortcuts; aggregate
functions for example are similarly lax, and in principle should gain
similar dependencies.  However, for now it seems sufficient to fix
the cast-versus-cast case, as pg_dump's other ordering heuristics
should keep it out of trouble for other object types.

Per report from David Turoň; thanks also to Robert Haas for
preliminary investigation.  I considered back-patching, but
seeing that this issue has existed for many years without
previous reports, it's not clear it's worth the trouble.
Moreover, back-patching wouldn't be enough to ensure that the
new pg_depend entries exist in existing databases anyway.

Discussion: https://postgr.es/m/OF0A160F3E.578B15D1-ONC12588DA.003E4857-C12588DA.0045A428@notes.linuxbox.cz

src/backend/catalog/pg_cast.c

@@ -35,13 +35,20 @@
  * Caller must have already checked privileges, and done consistency
  * checks on the given datatypes and cast function (if applicable).
  *
+ * Since we allow binary coercibility of the datatypes to the cast
+ * function's input and result, there could be one or two WITHOUT FUNCTION
+ * casts that this one depends on.  We don't record that explicitly
+ * in pg_cast, but we still need to make dependencies on those casts.
+ *
  * 'behavior' indicates the types of the dependencies that the new
- * cast will have on its input and output types and the cast function.
+ * cast will have on its input and output types, the cast function,
+ * and the other casts if any.
  * ----------------------------------------------------------------
  */
 ObjectAddress
-CastCreate(Oid sourcetypeid, Oid targettypeid, Oid funcid, char castcontext,
+CastCreate(Oid sourcetypeid, Oid targettypeid,
-		   char castmethod, DependencyType behavior)
+		   Oid funcid, Oid incastid, Oid outcastid,
+		   char castcontext, char castmethod, DependencyType behavior)
 {
 	Relation	relation;
 	HeapTuple	tuple;
@@ -102,6 +109,18 @@ CastCreate(Oid sourcetypeid, Oid targettypeid, Oid funcid, char castcontext,
 		add_exact_object_address(&referenced, addrs);
 	}
 
+	/* dependencies on casts required for function */
+	if (OidIsValid(incastid))
+	{
+		ObjectAddressSet(referenced, CastRelationId, incastid);
+		add_exact_object_address(&referenced, addrs);
+	}
+	if (OidIsValid(outcastid))
+	{
+		ObjectAddressSet(referenced, CastRelationId, outcastid);
+		add_exact_object_address(&referenced, addrs);
+	}
+
 	record_object_address_dependencies(&myself, addrs, behavior);
 	free_object_addresses(addrs);
 

src/backend/commands/functioncmds.c

@@ -1526,6 +1526,8 @@ CreateCast(CreateCastStmt *stmt)
 	char		sourcetyptype;
 	char		targettyptype;
 	Oid			funcid;
+	Oid			incastid = InvalidOid;
+	Oid			outcastid = InvalidOid;
 	int			nargs;
 	char		castcontext;
 	char		castmethod;
@@ -1603,7 +1605,9 @@ CreateCast(CreateCastStmt *stmt)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 					 errmsg("cast function must take one to three arguments")));
-		if (!IsBinaryCoercible(sourcetypeid, procstruct->proargtypes.values[0]))
+		if (!IsBinaryCoercibleWithCast(sourcetypeid,
+									   procstruct->proargtypes.values[0],
+									   &incastid))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 					 errmsg("argument of cast function must match or be binary-coercible from source data type")));
@@ -1617,7 +1621,9 @@ CreateCast(CreateCastStmt *stmt)
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 					 errmsg("third argument of cast function must be type %s",
 							"boolean")));
-		if (!IsBinaryCoercible(procstruct->prorettype, targettypeid))
+		if (!IsBinaryCoercibleWithCast(procstruct->prorettype,
+									   targettypeid,
+									   &outcastid))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 					 errmsg("return data type of cast function must match or be binary-coercible to target data type")));
@@ -1756,8 +1762,8 @@ CreateCast(CreateCastStmt *stmt)
 			break;
 	}
 
-	myself = CastCreate(sourcetypeid, targettypeid, funcid, castcontext,
+	myself = CastCreate(sourcetypeid, targettypeid, funcid, incastid, outcastid,
-						castmethod, DEPENDENCY_NORMAL);
+						castcontext, castmethod, DEPENDENCY_NORMAL);
 	return myself;
 }
 

src/backend/commands/typecmds.c

@@ -1705,7 +1705,9 @@ DefineRange(ParseState *pstate, CreateRangeStmt *stmt)
 							   &castFuncOid);
 
 	/* Create cast from the range type to its multirange type */
-	CastCreate(typoid, multirangeOid, castFuncOid, 'e', 'f', DEPENDENCY_INTERNAL);
+	CastCreate(typoid, multirangeOid, castFuncOid, InvalidOid, InvalidOid,
+			   COERCION_CODE_EXPLICIT, COERCION_METHOD_FUNCTION,
+			   DEPENDENCY_INTERNAL);
 
 	pfree(multirangeArrayName);
 

src/backend/parser/parse_coerce.c

@@ -2993,11 +2993,29 @@ IsPreferredType(TYPCATEGORY category, Oid type)
  */
 bool
 IsBinaryCoercible(Oid srctype, Oid targettype)
+{
+	Oid			castoid;
+
+	return IsBinaryCoercibleWithCast(srctype, targettype, &castoid);
+}
+
+/* IsBinaryCoercibleWithCast()
+ *		Check if srctype is binary-coercible to targettype.
+ *
+ * This variant also returns the OID of the pg_cast entry if one is involved.
+ * *castoid is set to InvalidOid if no binary-coercible cast exists, or if
+ * there is a hard-wired rule for it rather than a pg_cast entry.
+ */
+bool
+IsBinaryCoercibleWithCast(Oid srctype, Oid targettype,
+						  Oid *castoid)
 {
 	HeapTuple	tuple;
 	Form_pg_cast castForm;
 	bool		result;
 
+	*castoid = InvalidOid;
+
 	/* Fast path if same type */
 	if (srctype == targettype)
 		return true;
@@ -3061,6 +3079,9 @@ IsBinaryCoercible(Oid srctype, Oid targettype)
 	result = (castForm->castmethod == COERCION_METHOD_BINARY &&
 			  castForm->castcontext == COERCION_CODE_IMPLICIT);
 
+	if (result)
+		*castoid = castForm->oid;
+
 	ReleaseSysCache(tuple);
 
 	return result;

src/include/catalog/pg_cast.h

@@ -95,6 +95,8 @@ typedef enum CoercionMethod
 extern ObjectAddress CastCreate(Oid sourcetypeid,
 								Oid targettypeid,
 								Oid funcid,
+								Oid incastid,
+								Oid outcastid,
 								char castcontext,
 								char castmethod,
 								DependencyType behavior);

src/include/parser/parse_coerce.h

@@ -32,6 +32,8 @@ typedef enum CoercionPathType
 
 
 extern bool IsBinaryCoercible(Oid srctype, Oid targettype);
+extern bool IsBinaryCoercibleWithCast(Oid srctype, Oid targettype,
+									  Oid *castoid);
 extern bool IsPreferredType(TYPCATEGORY category, Oid type);
 extern TYPCATEGORY TypeCategory(Oid type);
 

src/test/regress/expected/create_cast.out

@@ -72,3 +72,32 @@ SELECT 1234::int4::casttesttype; -- Should work now
  foo1234
 (1 row)
 
+DROP FUNCTION int4_casttesttype(int4) CASCADE;
+NOTICE:  drop cascades to cast from integer to casttesttype
+-- Try it with a function that requires an implicit cast
+CREATE FUNCTION bar_int4_text(int4) RETURNS text LANGUAGE SQL AS
+$$ SELECT ('bar'::text || $1::text); $$;
+CREATE CAST (int4 AS casttesttype) WITH FUNCTION bar_int4_text(int4) AS IMPLICIT;
+SELECT 1234::int4::casttesttype; -- Should work now
+ casttesttype 
+--------------
+ bar1234
+(1 row)
+
+-- check dependencies generated for that
+SELECT pg_describe_object(classid, objid, objsubid) as obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as objref,
+       deptype
+FROM pg_depend
+WHERE classid = 'pg_cast'::regclass AND
+      objid = (SELECT oid FROM pg_cast
+               WHERE castsource = 'int4'::regtype
+                 AND casttarget = 'casttesttype'::regtype)
+ORDER BY refclassid;
+                obj                |             objref              | deptype 
+-----------------------------------+---------------------------------+---------
+ cast from integer to casttesttype | type casttesttype               | n
+ cast from integer to casttesttype | function bar_int4_text(integer) | n
+ cast from integer to casttesttype | cast from text to casttesttype  | n
+(3 rows)
+

src/test/regress/sql/create_cast.sql

@@ -52,3 +52,24 @@ $$ SELECT ('foo'::text || $1::text)::casttesttype; $$;
 
 CREATE CAST (int4 AS casttesttype) WITH FUNCTION int4_casttesttype(int4) AS IMPLICIT;
 SELECT 1234::int4::casttesttype; -- Should work now
+
+DROP FUNCTION int4_casttesttype(int4) CASCADE;
+
+-- Try it with a function that requires an implicit cast
+
+CREATE FUNCTION bar_int4_text(int4) RETURNS text LANGUAGE SQL AS
+$$ SELECT ('bar'::text || $1::text); $$;
+
+CREATE CAST (int4 AS casttesttype) WITH FUNCTION bar_int4_text(int4) AS IMPLICIT;
+SELECT 1234::int4::casttesttype; -- Should work now
+
+-- check dependencies generated for that
+SELECT pg_describe_object(classid, objid, objsubid) as obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as objref,
+       deptype
+FROM pg_depend
+WHERE classid = 'pg_cast'::regclass AND
+      objid = (SELECT oid FROM pg_cast
+               WHERE castsource = 'int4'::regtype
+                 AND casttarget = 'casttesttype'::regtype)
+ORDER BY refclassid;

src/tools/valgrind.supp

@@ -113,7 +113,7 @@
 	overread_tuplestruct_pg_cast
 	Memcheck:Addr4
 
-	fun:IsBinaryCoercible
+	fun:IsBinaryCoercibleWithCast
 }
 
 # Python's allocator does some low-level tricks for efficiency. Those