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

src/backend/utils/adt/array_selfuncs.c

@@ -39,25 +39,25 @@
 
 static Selectivity calc_arraycontsel(VariableStatData *vardata, Datum constval,
 									 Oid elemtype, Oid operator);
-static Selectivity mcelem_array_selec(ArrayType *array,
+static Selectivity mcelem_array_selec(const ArrayType *array,
 									  TypeCacheEntry *typentry,
-									  Datum *mcelem, int nmcelem,
-									  float4 *numbers, int nnumbers,
-									  float4 *hist, int nhist,
+									  const Datum *mcelem, int nmcelem,
+									  const float4 *numbers, int nnumbers,
+									  const float4 *hist, int nhist,
 									  Oid operator);
-static Selectivity mcelem_array_contain_overlap_selec(Datum *mcelem, int nmcelem,
-													  float4 *numbers, int nnumbers,
-													  Datum *array_data, int nitems,
+static Selectivity mcelem_array_contain_overlap_selec(const Datum *mcelem, int nmcelem,
+													  const float4 *numbers, int nnumbers,
+													  const Datum *array_data, int nitems,
 													  Oid operator, TypeCacheEntry *typentry);
-static Selectivity mcelem_array_contained_selec(Datum *mcelem, int nmcelem,
-												float4 *numbers, int nnumbers,
-												Datum *array_data, int nitems,
-												float4 *hist, int nhist,
+static Selectivity mcelem_array_contained_selec(const Datum *mcelem, int nmcelem,
+												const float4 *numbers, int nnumbers,
+												const Datum *array_data, int nitems,
+												const float4 *hist, int nhist,
 												Oid operator, TypeCacheEntry *typentry);
 static float *calc_hist(const float4 *hist, int nhist, int n);
 static float *calc_distr(const float *p, int n, int m, float rest);
 static int	floor_log2(uint32 n);
-static bool find_next_mcelem(Datum *mcelem, int nmcelem, Datum value,
+static bool find_next_mcelem(const Datum *mcelem, int nmcelem, Datum value,
 							 int *index, TypeCacheEntry *typentry);
 static int	element_compare(const void *key1, const void *key2, void *arg);
 static int	float_compare_desc(const void *key1, const void *key2);
@@ -425,10 +425,10 @@ calc_arraycontsel(VariableStatData *vardata, Datum constval,
  * mcelem_array_contained_selec depending on the operator.
  */
 static Selectivity
-mcelem_array_selec(ArrayType *array, TypeCacheEntry *typentry,
-				   Datum *mcelem, int nmcelem,
-				   float4 *numbers, int nnumbers,
-				   float4 *hist, int nhist,
+mcelem_array_selec(const ArrayType *array, TypeCacheEntry *typentry,
+				   const Datum *mcelem, int nmcelem,
+				   const float4 *numbers, int nnumbers,
+				   const float4 *hist, int nhist,
 				   Oid operator)
 {
 	Selectivity selec;
@@ -518,9 +518,9 @@ mcelem_array_selec(ArrayType *array, TypeCacheEntry *typentry,
  * fraction of nonempty arrays in the column.
  */
 static Selectivity
-mcelem_array_contain_overlap_selec(Datum *mcelem, int nmcelem,
-								   float4 *numbers, int nnumbers,
-								   Datum *array_data, int nitems,
+mcelem_array_contain_overlap_selec(const Datum *mcelem, int nmcelem,
+								   const float4 *numbers, int nnumbers,
+								   const Datum *array_data, int nitems,
 								   Oid operator, TypeCacheEntry *typentry)
 {
 	Selectivity selec,
@@ -699,10 +699,10 @@ mcelem_array_contain_overlap_selec(Datum *mcelem, int nmcelem,
  * ... * fn^on * (1 - fn)^(1 - on), o1, o2, ..., on) | o1 + o2 + .. on = m
  */
 static Selectivity
-mcelem_array_contained_selec(Datum *mcelem, int nmcelem,
-							 float4 *numbers, int nnumbers,
-							 Datum *array_data, int nitems,
-							 float4 *hist, int nhist,
+mcelem_array_contained_selec(const Datum *mcelem, int nmcelem,
+							 const float4 *numbers, int nnumbers,
+							 const Datum *array_data, int nitems,
+							 const float4 *hist, int nhist,
 							 Oid operator, TypeCacheEntry *typentry)
 {
 	int			mcelem_index,
@@ -1136,7 +1136,7 @@ floor_log2(uint32 n)
  * exact match.)
  */
 static bool
-find_next_mcelem(Datum *mcelem, int nmcelem, Datum value, int *index,
+find_next_mcelem(const Datum *mcelem, int nmcelem, Datum value, int *index,
 				 TypeCacheEntry *typentry)
 {
 	int			l = *index,

src/backend/utils/adt/arrayfuncs.c

@@ -960,8 +960,8 @@ ending_error:
  */
 void
 CopyArrayEls(ArrayType *array,
-			 Datum *values,
-			 bool *nulls,
+			 const Datum *values,
+			 const bool *nulls,
 			 int nitems,
 			 int typlen,
 			 bool typbyval,
@@ -3629,7 +3629,7 @@ construct_empty_expanded_array(Oid element_type,
  * to hard-wire values if the element type is hard-wired.
  */
 void
-deconstruct_array(ArrayType *array,
+deconstruct_array(const ArrayType *array,
 				  Oid elmtype,
 				  int elmlen, bool elmbyval, char elmalign,
 				  Datum **elemsp, bool **nullsp, int *nelemsp)
@@ -3695,7 +3695,7 @@ deconstruct_array(ArrayType *array,
  * useful when manipulating arrays from/for system catalogs.
  */
 void
-deconstruct_array_builtin(ArrayType *array,
+deconstruct_array_builtin(const ArrayType *array,
 						  Oid elmtype,
 						  Datum **elemsp, bool **nullsp, int *nelemsp)
 {
@@ -3765,7 +3765,7 @@ deconstruct_array_builtin(ArrayType *array,
  * if the array *might* contain a null.
  */
 bool
-array_contains_nulls(ArrayType *array)
+array_contains_nulls(const ArrayType *array)
 {
 	int			nelems;
 	bits8	   *bitmap;

src/backend/utils/adt/json.c

@@ -89,7 +89,7 @@ typedef struct JsonAggState
 static void composite_to_json(Datum composite, StringInfo result,
 							  bool use_line_feeds);
 static void array_dim_to_json(StringInfo result, int dim, int ndims, int *dims,
-							  Datum *vals, bool *nulls, int *valcount,
+							  const Datum *vals, const bool *nulls, int *valcount,
 							  JsonTypeCategory tcategory, Oid outfuncoid,
 							  bool use_line_feeds);
 static void array_to_json_internal(Datum array, StringInfo result,
@@ -429,8 +429,8 @@ JsonEncodeDateTime(char *buf, Datum value, Oid typid, const int *tzp)
  * ourselves recursively to process the next dimension.
  */
 static void
-array_dim_to_json(StringInfo result, int dim, int ndims, int *dims, Datum *vals,
-				  bool *nulls, int *valcount, JsonTypeCategory tcategory,
+array_dim_to_json(StringInfo result, int dim, int ndims, int *dims, const Datum *vals,
+				  const bool *nulls, int *valcount, JsonTypeCategory tcategory,
 				  Oid outfuncoid, bool use_line_feeds)
 {
 	int			i;

src/backend/utils/adt/jsonfuncs.c

@@ -477,16 +477,16 @@ static Datum populate_domain(DomainIOData *io, Oid typid, const char *colname,
 /* functions supporting jsonb_delete, jsonb_set and jsonb_concat */
 static JsonbValue *IteratorConcat(JsonbIterator **it1, JsonbIterator **it2,
 								  JsonbParseState **state);
-static JsonbValue *setPath(JsonbIterator **it, Datum *path_elems,
-						   bool *path_nulls, int path_len,
+static JsonbValue *setPath(JsonbIterator **it, const Datum *path_elems,
+						   const bool *path_nulls, int path_len,
 						   JsonbParseState **st, int level, JsonbValue *newval,
 						   int op_type);
-static void setPathObject(JsonbIterator **it, Datum *path_elems,
-						  bool *path_nulls, int path_len, JsonbParseState **st,
+static void setPathObject(JsonbIterator **it, const Datum *path_elems,
+						  const bool *path_nulls, int path_len, JsonbParseState **st,
 						  int level,
 						  JsonbValue *newval, uint32 npairs, int op_type);
-static void setPathArray(JsonbIterator **it, Datum *path_elems,
-						 bool *path_nulls, int path_len, JsonbParseState **st,
+static void setPathArray(JsonbIterator **it, const Datum *path_elems,
+						 const bool *path_nulls, int path_len, JsonbParseState **st,
 						 int level,
 						 JsonbValue *newval, uint32 nelems, int op_type);
 
@@ -1528,7 +1528,7 @@ get_jsonb_path_all(FunctionCallInfo fcinfo, bool as_text)
 }
 
 Datum
-jsonb_get_element(Jsonb *jb, Datum *path, int npath, bool *isnull, bool as_text)
+jsonb_get_element(Jsonb *jb, const Datum *path, int npath, bool *isnull, bool as_text)
 {
 	JsonbContainer *container = &jb->root;
 	JsonbValue *jbvp = NULL;
@@ -1676,7 +1676,7 @@ jsonb_get_element(Jsonb *jb, Datum *path, int npath, bool *isnull, bool as_text)
 }
 
 Datum
-jsonb_set_element(Jsonb *jb, Datum *path, int path_len,
+jsonb_set_element(Jsonb *jb, const Datum *path, int path_len,
 				  JsonbValue *newval)
 {
 	JsonbValue *res;
@@ -1718,8 +1718,8 @@ push_null_elements(JsonbParseState **ps, int num)
  * Caller is responsible to make sure such path does not exist yet.
  */
 static void
-push_path(JsonbParseState **st, int level, Datum *path_elems,
-		  bool *path_nulls, int path_len, JsonbValue *newval)
+push_path(JsonbParseState **st, int level, const Datum *path_elems,
+		  const bool *path_nulls, int path_len, JsonbValue *newval)
 {
 	/*
 	 * tpath contains expected type of an empty jsonb created at each level
@@ -5201,8 +5201,8 @@ IteratorConcat(JsonbIterator **it1, JsonbIterator **it2,
  * whatever bits in op_type are set, or nothing is done.
  */
 static JsonbValue *
-setPath(JsonbIterator **it, Datum *path_elems,
-		bool *path_nulls, int path_len,
+setPath(JsonbIterator **it, const Datum *path_elems,
+		const bool *path_nulls, int path_len,
 		JsonbParseState **st, int level, JsonbValue *newval, int op_type)
 {
 	JsonbValue	v;
@@ -5283,7 +5283,7 @@ setPath(JsonbIterator **it, Datum *path_elems,
  * Object walker for setPath
  */
 static void
-setPathObject(JsonbIterator **it, Datum *path_elems, bool *path_nulls,
+setPathObject(JsonbIterator **it, const Datum *path_elems, const bool *path_nulls,
 			  int path_len, JsonbParseState **st, int level,
 			  JsonbValue *newval, uint32 npairs, int op_type)
 {
@@ -5422,7 +5422,7 @@ setPathObject(JsonbIterator **it, Datum *path_elems, bool *path_nulls,
  * Array walker for setPath
  */
 static void
-setPathArray(JsonbIterator **it, Datum *path_elems, bool *path_nulls,
+setPathArray(JsonbIterator **it, const Datum *path_elems, const bool *path_nulls,
 			 int path_len, JsonbParseState **st, int level,
 			 JsonbValue *newval, uint32 nelems, int op_type)
 {

src/backend/utils/adt/multirangetypes_selfuncs.c

@@ -49,10 +49,10 @@ static float8 get_position(TypeCacheEntry *typcache, const RangeBound *value,
 static float8 get_len_position(double value, double hist1, double hist2);
 static float8 get_distance(TypeCacheEntry *typcache, const RangeBound *bound1,
 						   const RangeBound *bound2);
-static int	length_hist_bsearch(Datum *length_hist_values,
+static int	length_hist_bsearch(const Datum *length_hist_values,
 								int length_hist_nvalues, double value,
 								bool equal);
-static double calc_length_hist_frac(Datum *length_hist_values,
+static double calc_length_hist_frac(const Datum *length_hist_values,
 									int length_hist_nvalues, double length1,
 									double length2, bool equal);
 static double calc_hist_selectivity_contained(TypeCacheEntry *typcache,
@@ -60,14 +60,14 @@ static double calc_hist_selectivity_contained(TypeCacheEntry *typcache,
 											  RangeBound *upper,
 											  const RangeBound *hist_lower,
 											  int hist_nvalues,
-											  Datum *length_hist_values,
+											  const Datum *length_hist_values,
 											  int length_hist_nvalues);
 static double calc_hist_selectivity_contains(TypeCacheEntry *typcache,
 											 const RangeBound *lower,
 											 const RangeBound *upper,
 											 const RangeBound *hist_lower,
 											 int hist_nvalues,
-											 Datum *length_hist_values,
+											 const Datum *length_hist_values,
 											 int length_hist_nvalues);
 
 /*
@@ -765,7 +765,7 @@ rbound_bsearch(TypeCacheEntry *typcache, const RangeBound *value, const RangeBou
  * given length, returns -1.
  */
 static int
-length_hist_bsearch(Datum *length_hist_values, int length_hist_nvalues,
+length_hist_bsearch(const Datum *length_hist_values, int length_hist_nvalues,
 					double value, bool equal)
 {
 	int			lower = -1,
@@ -963,7 +963,7 @@ get_distance(TypeCacheEntry *typcache, const RangeBound *bound1, const RangeBoun
  * 'equal' is true).
  */
 static double
-calc_length_hist_frac(Datum *length_hist_values, int length_hist_nvalues,
+calc_length_hist_frac(const Datum *length_hist_values, int length_hist_nvalues,
 					  double length1, double length2, bool equal)
 {
 	double		frac;
@@ -1131,7 +1131,7 @@ static double
 calc_hist_selectivity_contained(TypeCacheEntry *typcache,
 								const RangeBound *lower, RangeBound *upper,
 								const RangeBound *hist_lower, int hist_nvalues,
-								Datum *length_hist_values, int length_hist_nvalues)
+								const Datum *length_hist_values, int length_hist_nvalues)
 {
 	int			i,
 				upper_index;
@@ -1252,7 +1252,7 @@ static double
 calc_hist_selectivity_contains(TypeCacheEntry *typcache,
 							   const RangeBound *lower, const RangeBound *upper,
 							   const RangeBound *hist_lower, int hist_nvalues,
-							   Datum *length_hist_values, int length_hist_nvalues)
+							   const Datum *length_hist_values, int length_hist_nvalues)
 {
 	int			i,
 				lower_index;

src/backend/utils/adt/network_selfuncs.c

@@ -48,17 +48,17 @@ static Selectivity networkjoinsel_inner(Oid operator,
 static Selectivity networkjoinsel_semi(Oid operator,
 									   VariableStatData *vardata1, VariableStatData *vardata2);
 static Selectivity mcv_population(float4 *mcv_numbers, int mcv_nvalues);
-static Selectivity inet_hist_value_sel(Datum *values, int nvalues,
+static Selectivity inet_hist_value_sel(const Datum *values, int nvalues,
 									   Datum constvalue, int opr_codenum);
 static Selectivity inet_mcv_join_sel(Datum *mcv1_values,
 									 float4 *mcv1_numbers, int mcv1_nvalues, Datum *mcv2_values,
 									 float4 *mcv2_numbers, int mcv2_nvalues, Oid operator);
-static Selectivity inet_mcv_hist_sel(Datum *mcv_values, float4 *mcv_numbers,
-									 int mcv_nvalues, Datum *hist_values, int hist_nvalues,
+static Selectivity inet_mcv_hist_sel(const Datum *mcv_values, float4 *mcv_numbers,
+									 int mcv_nvalues, const Datum *hist_values, int hist_nvalues,
 									 int opr_codenum);
-static Selectivity inet_hist_inclusion_join_sel(Datum *hist1_values,
+static Selectivity inet_hist_inclusion_join_sel(const Datum *hist1_values,
 												int hist1_nvalues,
-												Datum *hist2_values, int hist2_nvalues,
+												const Datum *hist2_values, int hist2_nvalues,
 												int opr_codenum);
 static Selectivity inet_semi_join_sel(Datum lhs_value,
 									  bool mcv_exists, Datum *mcv_values, int mcv_nvalues,
@@ -601,7 +601,7 @@ mcv_population(float4 *mcv_numbers, int mcv_nvalues)
  * better option than not considering these buckets at all.
  */
 static Selectivity
-inet_hist_value_sel(Datum *values, int nvalues, Datum constvalue,
+inet_hist_value_sel(const Datum *values, int nvalues, Datum constvalue,
 					int opr_codenum)
 {
 	Selectivity match = 0.0;
@@ -702,8 +702,8 @@ inet_mcv_join_sel(Datum *mcv1_values, float4 *mcv1_numbers, int mcv1_nvalues,
  * the histogram.
  */
 static Selectivity
-inet_mcv_hist_sel(Datum *mcv_values, float4 *mcv_numbers, int mcv_nvalues,
-				  Datum *hist_values, int hist_nvalues,
+inet_mcv_hist_sel(const Datum *mcv_values, float4 *mcv_numbers, int mcv_nvalues,
+				  const Datum *hist_values, int hist_nvalues,
 				  int opr_codenum)
 {
 	Selectivity selec = 0.0;
@@ -739,8 +739,8 @@ inet_mcv_hist_sel(Datum *mcv_values, float4 *mcv_numbers, int mcv_nvalues,
  * average?  That would at least avoid non-commutative estimation results.
  */
 static Selectivity
-inet_hist_inclusion_join_sel(Datum *hist1_values, int hist1_nvalues,
-							 Datum *hist2_values, int hist2_nvalues,
+inet_hist_inclusion_join_sel(const Datum *hist1_values, int hist1_nvalues,
+							 const Datum *hist2_values, int hist2_nvalues,
 							 int opr_codenum)
 {
 	double		match = 0.0;

src/backend/utils/adt/orderedsetaggs.c

@@ -660,8 +660,8 @@ pct_info_cmp(const void *pa, const void *pb)
  */
 static struct pct_info *
 setup_pct_info(int num_percentiles,
-			   Datum *percentiles_datum,
-			   bool *percentiles_null,
+			   const Datum *percentiles_datum,
+			   const bool *percentiles_null,
 			   int64 rowcount,
 			   bool continuous)
 {

src/backend/utils/adt/rangetypes_selfuncs.c

@@ -46,18 +46,18 @@ static float8 get_position(TypeCacheEntry *typcache, const RangeBound *value,
 static float8 get_len_position(double value, double hist1, double hist2);
 static float8 get_distance(TypeCacheEntry *typcache, const RangeBound *bound1,
 						   const RangeBound *bound2);
-static int	length_hist_bsearch(Datum *length_hist_values,
+static int	length_hist_bsearch(const Datum *length_hist_values,
 								int length_hist_nvalues, double value, bool equal);
-static double calc_length_hist_frac(Datum *length_hist_values,
+static double calc_length_hist_frac(const Datum *length_hist_values,
 									int length_hist_nvalues, double length1, double length2, bool equal);
 static double calc_hist_selectivity_contained(TypeCacheEntry *typcache,
 											  const RangeBound *lower, RangeBound *upper,
 											  const RangeBound *hist_lower, int hist_nvalues,
-											  Datum *length_hist_values, int length_hist_nvalues);
+											  const Datum *length_hist_values, int length_hist_nvalues);
 static double calc_hist_selectivity_contains(TypeCacheEntry *typcache,
 											 const RangeBound *lower, const RangeBound *upper,
 											 const RangeBound *hist_lower, int hist_nvalues,
-											 Datum *length_hist_values, int length_hist_nvalues);
+											 const Datum *length_hist_values, int length_hist_nvalues);
 
 /*
  * Returns a default selectivity estimate for given operator, when we don't
@@ -654,7 +654,7 @@ rbound_bsearch(TypeCacheEntry *typcache, const RangeBound *value, const RangeBou
  * given length, returns -1.
  */
 static int
-length_hist_bsearch(Datum *length_hist_values, int length_hist_nvalues,
+length_hist_bsearch(const Datum *length_hist_values, int length_hist_nvalues,
 					double value, bool equal)
 {
 	int			lower = -1,
@@ -852,7 +852,7 @@ get_distance(TypeCacheEntry *typcache, const RangeBound *bound1, const RangeBoun
  * 'equal' is true).
  */
 static double
-calc_length_hist_frac(Datum *length_hist_values, int length_hist_nvalues,
+calc_length_hist_frac(const Datum *length_hist_values, int length_hist_nvalues,
 					  double length1, double length2, bool equal)
 {
 	double		frac;
@@ -1018,7 +1018,7 @@ static double
 calc_hist_selectivity_contained(TypeCacheEntry *typcache,
 								const RangeBound *lower, RangeBound *upper,
 								const RangeBound *hist_lower, int hist_nvalues,
-								Datum *length_hist_values, int length_hist_nvalues)
+								const Datum *length_hist_values, int length_hist_nvalues)
 {
 	int			i,
 				upper_index;
@@ -1139,7 +1139,7 @@ static double
 calc_hist_selectivity_contains(TypeCacheEntry *typcache,
 							   const RangeBound *lower, const RangeBound *upper,
 							   const RangeBound *hist_lower, int hist_nvalues,
-							   Datum *length_hist_values, int length_hist_nvalues)
+							   const Datum *length_hist_values, int length_hist_nvalues)
 {
 	int			i,
 				lower_index;

src/backend/utils/adt/xml.c

@@ -891,8 +891,8 @@ xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
 
 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)
 {
 #ifdef USE_LIBXML
 	xmltype    *result;