Remove traces of version-0 calling convention in src/tutorial/

Support has been removed as of 5ded4bd, but code related to the tutorial
still used it.  Functions using version-1 are already present for some
time in the tutorial, and the documentation mentions them, so just
replace the old version with the new one.

Reported-by: Pavel Stehule
Analyzed-by: Euler Taveira
Author: Michael Paquier
Reviewed-by: Tom Lane, Pavel Stehule
Discussion: https://postgr.es/m/CAFj8pRCgC2uDzrw-vvanXu6Z3ofyviEOQPEpH6_aL4OCe7JRag@mail.gmail.com

Author: michaelpq

src/tutorial/funcs.c

@@ -6,9 +6,6 @@
 
   The calling format for these functions is defined by the CREATE FUNCTION
   SQL statement that binds them to the backend.
-
-  NOTE: this file shows examples of "old style" function call conventions.
-  See funcs_new.c for examples of "new style".
 *****************************************************************************/
 
 #include "postgres.h"			/* general Postgres declarations */
@@ -18,94 +15,112 @@
 
 PG_MODULE_MAGIC;
 
-/* These prototypes just prevent possible warnings from gcc. */
-
-int			add_one(int arg);
-float8	   *add_one_float8(float8 *arg);
-Point	   *makepoint(Point *pointx, Point *pointy);
-text	   *copytext(text *t);
-text	   *concat_text(text *arg1, text *arg2);
-bool		c_overpaid(HeapTupleHeader t,	/* the current instance of EMP */
-					   int32 limit);
-
 
 /* By Value */
 
-int
-add_one(int arg)
+PG_FUNCTION_INFO_V1(add_one);
+
+Datum
+add_one(PG_FUNCTION_ARGS)
 {
-	return arg + 1;
+	int32		arg = PG_GETARG_INT32(0);
+
+	PG_RETURN_INT32(arg + 1);
 }
 
 /* By Reference, Fixed Length */
 
-float8 *
-add_one_float8(float8 *arg)
-{
-	float8	   *result = (float8 *) palloc(sizeof(float8));
+PG_FUNCTION_INFO_V1(add_one_float8);
 
-	*result = *arg + 1.0;
+Datum
+add_one_float8(PG_FUNCTION_ARGS)
+{
+	/* The macros for FLOAT8 hide its pass-by-reference nature */
+	float8		arg = PG_GETARG_FLOAT8(0);
 
-	return result;
+	PG_RETURN_FLOAT8(arg + 1.0);
 }
 
-Point *
-makepoint(Point *pointx, Point *pointy)
+PG_FUNCTION_INFO_V1(makepoint);
+
+Datum
+makepoint(PG_FUNCTION_ARGS)
 {
+	Point	   *pointx = PG_GETARG_POINT_P(0);
+	Point	   *pointy = PG_GETARG_POINT_P(1);
 	Point	   *new_point = (Point *) palloc(sizeof(Point));
 
 	new_point->x = pointx->x;
 	new_point->y = pointy->y;
 
-	return new_point;
+	PG_RETURN_POINT_P(new_point);
 }
 
 /* By Reference, Variable Length */
 
-text *
-copytext(text *t)
+PG_FUNCTION_INFO_V1(copytext);
+
+Datum
+copytext(PG_FUNCTION_ARGS)
 {
+	text	   *t = PG_GETARG_TEXT_PP(0);
+
 	/*
-	 * VARSIZE is the total size of the struct in bytes.
+	 * VARSIZE_ANY_EXHDR is the size of the struct in bytes, minus the
+	 * VARHDRSZ or VARHDRSZ_SHORT of its header.  Construct the copy with a
+	 * full-length header.
 	 */
-	text	   *new_t = (text *) palloc(VARSIZE(t));
+	text	   *new_t = (text *) palloc(VARSIZE_ANY_EXHDR(t) + VARHDRSZ);
 
-	SET_VARSIZE(new_t, VARSIZE(t));
+	SET_VARSIZE(new_t, VARSIZE_ANY_EXHDR(t) + VARHDRSZ);
 
 	/*
-	 * VARDATA is a pointer to the data region of the struct.
+	 * VARDATA is a pointer to the data region of the new struct.  The source
+	 * could be a short datum, so retrieve its data through VARDATA_ANY.
 	 */
 	memcpy((void *) VARDATA(new_t), /* destination */
-		   (void *) VARDATA(t), /* source */
-		   VARSIZE(t) - VARHDRSZ);	/* how many bytes */
-	return new_t;
+		   (void *) VARDATA_ANY(t), /* source */
+		   VARSIZE_ANY_EXHDR(t));	/* how many bytes */
+	PG_RETURN_TEXT_P(new_t);
 }
 
-text *
-concat_text(text *arg1, text *arg2)
+PG_FUNCTION_INFO_V1(concat_text);
+
+Datum
+concat_text(PG_FUNCTION_ARGS)
 {
-	int32		arg1_size = VARSIZE(arg1) - VARHDRSZ;
-	int32		arg2_size = VARSIZE(arg2) - VARHDRSZ;
+	text	   *arg1 = PG_GETARG_TEXT_PP(0);
+	text	   *arg2 = PG_GETARG_TEXT_PP(1);
+	int32		arg1_size = VARSIZE_ANY_EXHDR(arg1);
+	int32		arg2_size = VARSIZE_ANY_EXHDR(arg2);
 	int32		new_text_size = arg1_size + arg2_size + VARHDRSZ;
 	text	   *new_text = (text *) palloc(new_text_size);
 
 	SET_VARSIZE(new_text, new_text_size);
-	memcpy(VARDATA(new_text), VARDATA(arg1), arg1_size);
-	memcpy(VARDATA(new_text) + arg1_size, VARDATA(arg2), arg2_size);
-	return new_text;
+	memcpy(VARDATA(new_text), VARDATA_ANY(arg1), arg1_size);
+	memcpy(VARDATA(new_text) + arg1_size, VARDATA_ANY(arg2), arg2_size);
+	PG_RETURN_TEXT_P(new_text);
 }
 
 /* Composite types */
 
-bool
-c_overpaid(HeapTupleHeader t,	/* the current instance of EMP */
-		   int32 limit)
+PG_FUNCTION_INFO_V1(c_overpaid);
+
+Datum
+c_overpaid(PG_FUNCTION_ARGS)
 {
+	HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER(0);
+	int32		limit = PG_GETARG_INT32(1);
 	bool		isnull;
 	int32		salary;
 
 	salary = DatumGetInt32(GetAttributeByName(t, "salary", &isnull));
 	if (isnull)
-		return false;
-	return salary > limit;
+		PG_RETURN_BOOL(false);
+
+	/*
+	 * Alternatively, we might prefer to do PG_RETURN_NULL() for null salary
+	 */
+
+	PG_RETURN_BOOL(salary > limit);
 }