Mark function arguments of type "Datum *" as "const Datum *" where possible

Several functions in the codebase accept "Datum *" parameters but do
not modify the pointed-to data.  These have been updated to take
"const Datum *" instead, improving type safety and making the
interfaces clearer about their intent.  This change helps the compiler
catch accidental modifications and better documents immutability of
arguments.

Most of "Datum *" parameters have a pairing "bool *isnull" parameter,
they are constified as well.

No functional behavior is changed by this patch.

Author: Chao Li <lic@highgo.com>
Discussion: https://www.postgresql.org/message-id/flat/CAEoWx2msfT0knvzUa72ZBwu9LR_RLY4on85w2a9YpE-o2By5HQ@mail.gmail.com

3 files changed, 9 insertions, 9 deletions

diff --git a/src/include/utils/array.h b/src/include/utils/array.h
index 3383f16a3bb..67d11a78ba4 100644
--- a/src/include/utils/array.h
+++ b/src/include/utils/array.h
@@ -352,8 +352,8 @@ extern PGDLLIMPORT bool Array_nulls;
  * prototypes for functions defined in arrayfuncs.c
  */
 extern void CopyArrayEls(ArrayType *array,
-						 Datum *values,
-						 bool *nulls,
+						 const Datum *values,
+						 const bool *nulls,
 						 int nitems,
 						 int typlen,
 						 bool typbyval,
@@ -405,14 +405,14 @@ extern ArrayType *construct_empty_array(Oid elmtype);
 extern ExpandedArrayHeader *construct_empty_expanded_array(Oid element_type,
 														   MemoryContext parentcontext,
 														   ArrayMetaState *metacache);
-extern void deconstruct_array(ArrayType *array,
+extern void deconstruct_array(const ArrayType *array,
 							  Oid elmtype,
 							  int elmlen, bool elmbyval, char elmalign,
 							  Datum **elemsp, bool **nullsp, int *nelemsp);
-extern void deconstruct_array_builtin(ArrayType *array,
+extern void deconstruct_array_builtin(const ArrayType *array,
 									  Oid elmtype,
 									  Datum **elemsp, bool **nullsp, int *nelemsp);
-extern bool array_contains_nulls(ArrayType *array);
+extern bool array_contains_nulls(const ArrayType *array);
 
 extern ArrayBuildState *initArrayResult(Oid element_type,
 										MemoryContext rcontext, bool subcontext);
diff --git a/src/include/utils/jsonb.h b/src/include/utils/jsonb.h
index fecb33b9c67..ff30fbcf6df 100644
--- a/src/include/utils/jsonb.h
+++ b/src/include/utils/jsonb.h
@@ -426,9 +426,9 @@ extern char *JsonbUnquote(Jsonb *jb);
 extern bool JsonbExtractScalar(JsonbContainer *jbc, JsonbValue *res);
 extern const char *JsonbTypeName(JsonbValue *val);
 
-extern Datum jsonb_set_element(Jsonb *jb, Datum *path, int path_len,
+extern Datum jsonb_set_element(Jsonb *jb, const Datum *path, int path_len,
 							   JsonbValue *newval);
-extern Datum jsonb_get_element(Jsonb *jb, Datum *path, int npath,
+extern Datum jsonb_get_element(Jsonb *jb, const Datum *path, int npath,
 							   bool *isnull, bool as_text);
 extern bool to_jsonb_is_immutable(Oid typoid);
 extern Datum jsonb_build_object_worker(int nargs, const Datum *args, const bool *nulls,
diff --git a/src/include/utils/xml.h b/src/include/utils/xml.h
index 0d7a816b9f9..732dac47bc4 100644
--- a/src/include/utils/xml.h
+++ b/src/include/utils/xml.h
@@ -71,8 +71,8 @@ extern void xml_ereport(PgXmlErrorContext *errcxt, int level, int sqlcode,
 
 extern xmltype *xmlconcat(List *args);
 extern xmltype *xmlelement(XmlExpr *xexpr,
-						   Datum *named_argvalue, bool *named_argnull,
-						   Datum *argvalue, bool *argnull);
+						   const Datum *named_argvalue, const bool *named_argnull,
+						   const Datum *argvalue, const bool *argnull);
 extern xmltype *xmlparse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace);
 extern xmltype *xmlpi(const char *target, text *arg, bool arg_is_null, bool *result_is_null);
 extern xmltype *xmlroot(xmltype *data, text *version, int standalone);