numeric-scale-v3-delta.patch

diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 6abda2f1d2..d3c70667a3 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -545,8 +545,8 @@
 <programlisting>
 NUMERIC(<replaceable>precision</replaceable>, <replaceable>scale</replaceable>)
 </programlisting>
-     The precision must be positive, the scale may be positive or negative
-     (see below).  Alternatively:
+     The precision must be positive, while the scale may be positive or
+     negative (see below).  Alternatively:
 <programlisting>
 NUMERIC(<replaceable>precision</replaceable>)
 </programlisting>
@@ -569,8 +569,8 @@ NUMERIC
     <note>
      <para>
       The maximum precision that can be explicitly specified in
-      a <type>NUMERIC</type> type declaration is 1000.  An
-      unconstrained <type>NUMERIC</type> column is subject to the limits
+      a <type>numeric</type> type declaration is 1000.  An
+      unconstrained <type>numeric</type> column is subject to the limits
       described in <xref linkend="datatype-numeric-table"/>.
      </para>
     </note>
@@ -578,38 +578,48 @@ NUMERIC
     <para>
      If the scale of a value to be stored is greater than the declared
      scale of the column, the system will round the value to the specified
-     number of fractional digits.  If the declared scale of the column is
-     negative, the value will be rounded to the left of the decimal point.
-     If, after rounding, the number of digits to the left of the decimal point
-     exceeds the declared precision minus the declared scale, an error is
-     raised.  Similarly, if the declared scale exceeds the declared precision
-     and the number of zero digits to the right of the decimal point is less
-     than the declared scale minus the declared precision, an error is raised.
+     number of fractional digits.  Then, if the number of digits to the
+     left of the decimal point exceeds the declared precision minus the
+     declared scale, an error is raised.
      For example, a column declared as
 <programlisting>
 NUMERIC(3, 1)
 </programlisting>
-     will round values to 1 decimal place and be able to store values between
-     -99.9 and 99.9, inclusive.  A column declared as
+     will round values to 1 decimal place and can store values between
+     -99.9 and 99.9, inclusive.
+    </para>
+
+    <para>
+     Beginning in <productname>PostgreSQL</productname> 15, it is allowed
+     to declare a <type>numeric</type> column with a negative scale.  Then
+     values will be rounded to the left of the decimal point.  The
+     precision still represents the maximum number of non-rounded digits.
+     Thus, a column declared as
 <programlisting>
 NUMERIC(2, -3)
 </programlisting>
-     will round values to the nearest thousand and be able to store values
-     between -99000 and 99000, inclusive.  A column declared as
+     will round values to the nearest thousand and can store values
+     between -99000 and 99000, inclusive.
+     It is also allowed to declare a scale larger than the declared
+     precision.  Such a column can only hold fractional values, and it
+     requires the number of zero digits just to the right of the decimal
+     point to be at least the declared scale minus the declared precision.
+     For example, a column declared as
 <programlisting>
 NUMERIC(3, 5)
 </programlisting>
-     will round values to 5 decimal places and be able to store values between
+     will round values to 5 decimal places and can store values between
      -0.00999 and 0.00999, inclusive.
     </para>
 
     <note>
      <para>
-      The scale in a <type>NUMERIC</type> type declaration may be any value in
-      the range -1000 to 1000.  (The <acronym>SQL</acronym> standard requires
-      the scale to be in the range 0 to <replaceable>precision</replaceable>.
-      Using values outside this range may not be portable to other database
-      systems.)
+      <productname>PostgreSQL</productname> permits the scale in
+      a <type>numeric</type> type declaration to be any value in the range
+      -1000 to 1000.  However, the <acronym>SQL</acronym> standard requires
+      the scale to be in the range 0
+      to <replaceable>precision</replaceable>.  Using scales outside that
+      range may not be portable to other database systems.
      </para>
     </note>
 
diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 46cb37cea1..faff09f5d5 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -827,21 +827,31 @@ numeric_is_integral(Numeric num)
  *
  *	For purely historical reasons VARHDRSZ is then added to the result, thus
  *	the unused space in the upper 16 bits is not all as freely available as it
- *	might seem.
+ *	might seem.  (We can't let the result overflow to a negative int32, as
+ *	other parts of the system would interpret that as not-a-valid-typmod.)
  */
-static inline int
+static inline int32
 make_numeric_typmod(int precision, int scale)
 {
 	return ((precision << 16) | (scale & 0x7ff)) + VARHDRSZ;
 }
 
+/*
+ * Because of the offset, valid numeric typmods are at least VARHDRSZ
+ */
+static inline bool
+is_valid_numeric_typmod(int32 typmod)
+{
+	return typmod >= (int32) VARHDRSZ;
+}
+
 /*
  * numeric_typmod_precision() -
  *
  *	Extract the precision from a numeric typmod --- see make_numeric_typmod().
  */
 static inline int
-numeric_typmod_precision(int typmod)
+numeric_typmod_precision(int32 typmod)
 {
 	return ((typmod - VARHDRSZ) >> 16) & 0xffff;
 }
@@ -856,7 +866,7 @@ numeric_typmod_precision(int typmod)
  *	extends an 11-bit two's complement number x.
  */
 static inline int
-numeric_typmod_scale(int typmod)
+numeric_typmod_scale(int32 typmod)
 {
 	return (((typmod - VARHDRSZ) & 0x7ff) ^ 1024) - 1024;
 }
@@ -872,7 +882,7 @@ numeric_maximum_size(int32 typmod)
 	int			precision;
 	int			numeric_digits;
 
-	if (typmod < (int32) (VARHDRSZ))
+	if (!is_valid_numeric_typmod(typmod))
 		return -1;
 
 	/* precision (ie, max # of digits) is in upper bits of typmod */
@@ -1136,14 +1146,14 @@ numeric_support(PG_FUNCTION_ARGS)
 			int32		new_precision = numeric_typmod_precision(new_typmod);
 
 			/*
-			 * If new_typmod < VARHDRSZ, the destination is unconstrained;
-			 * that's always OK.  If old_typmod >= VARHDRSZ, the source is
+			 * If new_typmod is invalid, the destination is unconstrained;
+			 * that's always OK.  If old_typmod is valid, the source is
 			 * constrained, and we're OK if the scale is unchanged and the
 			 * precision is not decreasing.  See further notes in function
 			 * header comment.
 			 */
-			if (new_typmod < (int32) VARHDRSZ ||
-				(old_typmod >= (int32) VARHDRSZ &&
+			if (!is_valid_numeric_typmod(new_typmod) ||
+				(is_valid_numeric_typmod(old_typmod) &&
 				 new_scale == old_scale && new_precision >= old_precision))
 				ret = relabel_to_typmod(source, new_typmod);
 		}
@@ -1186,7 +1196,7 @@ numeric		(PG_FUNCTION_ARGS)
 	 * If the value isn't a valid type modifier, simply return a copy of the
 	 * input value
 	 */
-	if (typmod < (int32) (VARHDRSZ))
+	if (!is_valid_numeric_typmod(typmod))
 		PG_RETURN_NUMERIC(duplicate_numeric(num));
 
 	/*
@@ -1288,7 +1298,7 @@ numerictypmodout(PG_FUNCTION_ARGS)
 	int32		typmod = PG_GETARG_INT32(0);
 	char	   *res = (char *) palloc(64);
 
-	if (typmod >= 0)
+	if (is_valid_numeric_typmod(typmod))
 		snprintf(res, 64, "(%d,%d)",
 				 numeric_typmod_precision(typmod),
 				 numeric_typmod_scale(typmod));
@@ -7476,8 +7486,8 @@ apply_typmod(NumericVar *var, int32 typmod)
 	int			ddigits;
 	int			i;
 
-	/* Do nothing if we have a default typmod (-1) */
-	if (typmod < (int32) (VARHDRSZ))
+	/* Do nothing if we have an invalid typmod */
+	if (!is_valid_numeric_typmod(typmod))
 		return;
 
 	precision = numeric_typmod_precision(typmod);
@@ -7565,7 +7575,7 @@ apply_typmod_special(Numeric num, int32 typmod)
 		return;
 
 	/* Do nothing if we have a default typmod (-1) */
-	if (typmod < (int32) (VARHDRSZ))
+	if (!is_valid_numeric_typmod(typmod))
 		return;
 
 	precision = numeric_typmod_precision(typmod);