Introduce macros for typalign and typstorage constants.

Our usual practice for "poor man's enum" catalog columns is to define
macros for the possible values and use those, not literal constants,
in C code.  But for some reason lost in the mists of time, this was
never done for typalign/attalign or typstorage/attstorage.  It's never
too late to make it better though, so let's do that.

The reason I got interested in this right now is the need to duplicate
some uses of the TYPSTORAGE constants in an upcoming ALTER TYPE patch.
But in general, this sort of change aids greppability and readability,
so it's a good idea even without any specific motivation.

I may have missed a few places that could be converted, and it's even
more likely that pending patches will re-introduce some hard-coded
references.  But that's not fatal --- there's no expectation that
we'd actually change any of these values.  We can clean up stragglers
over time.

Discussion: https://postgr.es/m/16457.1583189537@sss.pgh.pa.us

src/include/access/toast_helper.h

@@ -20,12 +20,12 @@
  * Information about one column of a tuple being toasted.
  *
  * NOTE: toast_action[i] can have these values:
- *		' '		default handling
- *		'p'		already processed --- don't touch it
- *		'x'		incompressible, but OK to move off
+ *		' '						default handling
+ *		TYPSTORAGE_PLAIN		already processed --- don't touch it
+ *		TYPSTORAGE_EXTENDED		incompressible, but OK to move off
  *
  * NOTE: toast_attr[i].tai_size is only made valid for varlena attributes with
- * toast_action[i] different from 'p'.
+ * toast_action[i] different from TYPSTORAGE_PLAIN.
  */
 typedef struct
 {

src/include/access/tupmacs.h

@@ -14,6 +14,8 @@
 #ifndef TUPMACS_H
 #define TUPMACS_H
 
+#include "catalog/pg_type_d.h"	/* for TYPALIGN macros */
+
 
 /*
  * Check a tuple's null bitmap to determine whether the attribute is null.
@@ -145,11 +147,11 @@
  */
 #define att_align_nominal(cur_offset, attalign) \
 ( \
-	((attalign) == 'i') ? INTALIGN(cur_offset) : \
-	 (((attalign) == 'c') ? (uintptr_t) (cur_offset) : \
-	  (((attalign) == 'd') ? DOUBLEALIGN(cur_offset) : \
+	((attalign) == TYPALIGN_INT) ? INTALIGN(cur_offset) : \
+	 (((attalign) == TYPALIGN_CHAR) ? (uintptr_t) (cur_offset) : \
+	  (((attalign) == TYPALIGN_DOUBLE) ? DOUBLEALIGN(cur_offset) : \
 	   ( \
-			AssertMacro((attalign) == 's'), \
+			AssertMacro((attalign) == TYPALIGN_SHORT), \
 			SHORTALIGN(cur_offset) \
 	   ))) \
 )

src/include/catalog/pg_attribute.h

@@ -110,14 +110,7 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	/*----------
 	 * attstorage tells for VARLENA attributes, what the heap access
 	 * methods can do to it if a given tuple doesn't fit into a page.
-	 * Possible values are
-	 *		'p': Value must be stored plain always
-	 *		'e': Value can be stored in "secondary" relation (if relation
-	 *			 has one, see pg_class.reltoastrelid)
-	 *		'm': Value can be stored compressed inline
-	 *		'x': Value can be stored compressed inline or in "secondary"
-	 * Note that 'm' fields can also be moved out to secondary storage,
-	 * but only as a last resort ('e' and 'x' fields are moved first).
+	 * Possible values are as for pg_type.typstorage (see TYPSTORAGE macros).
 	 *----------
 	 */
 	char		attstorage;

src/include/catalog/pg_type.h

@@ -155,6 +155,7 @@ CATALOG(pg_type,1247,TypeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(71,TypeRelati
 	 * 's' = SHORT alignment (2 bytes on most machines).
 	 * 'i' = INT alignment (4 bytes on most machines).
 	 * 'd' = DOUBLE alignment (8 bytes on many machines, but by no means all).
+	 * (Use the TYPALIGN macros below for these.)
 	 *
 	 * See include/access/tupmacs.h for the macros that compute these
 	 * alignment requirements.  Note also that we allow the nominal alignment
@@ -176,6 +177,10 @@ CATALOG(pg_type,1247,TypeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(71,TypeRelati
 	 * 'e' EXTERNAL   external storage possible, don't try to compress
 	 * 'x' EXTENDED   try to compress and store external if required
 	 * 'm' MAIN		  like 'x' but try to keep in main tuple
+	 * (Use the TYPSTORAGE macros below for these.)
+	 *
+	 * Note that 'm' fields can also be moved out to secondary storage,
+	 * but only as a last resort ('e' and 'x' fields are moved first).
 	 * ----------------
 	 */
 	char		typstorage BKI_DEFAULT(p) BKI_ARRAY_DEFAULT(x);
@@ -278,6 +283,16 @@ typedef FormData_pg_type *Form_pg_type;
 #define  TYPCATEGORY_BITSTRING	'V' /* er ... "varbit"? */
 #define  TYPCATEGORY_UNKNOWN	'X'
 
+#define  TYPALIGN_CHAR			'c' /* char alignment (i.e. unaligned) */
+#define  TYPALIGN_SHORT			's' /* short alignment (typically 2 bytes) */
+#define  TYPALIGN_INT			'i' /* int alignment (typically 4 bytes) */
+#define  TYPALIGN_DOUBLE		'd' /* double alignment (often 8 bytes) */
+
+#define  TYPSTORAGE_PLAIN		'p' /* type not prepared for toasting */
+#define  TYPSTORAGE_EXTERNAL	'e' /* toastable, don't try to compress */
+#define  TYPSTORAGE_EXTENDED	'x' /* fully toastable */
+#define  TYPSTORAGE_MAIN		'm' /* like 'x' but try to store inline */
+
 /* Is a type OID a polymorphic pseudotype?	(Beware of multiple evaluation) */
 #define IsPolymorphicType(typid)  \
 	((typid) == ANYELEMENTOID || \

src/include/utils/lsyscache.h

@@ -186,6 +186,6 @@ extern Oid	get_index_column_opclass(Oid index_oid, int attno);
 /* type_is_array_domain accepts both plain arrays and domains over arrays */
 #define type_is_array_domain(typid)  (get_base_element_type(typid) != InvalidOid)
 
-#define TypeIsToastable(typid)	(get_typstorage(typid) != 'p')
+#define TypeIsToastable(typid)	(get_typstorage(typid) != TYPSTORAGE_PLAIN)
 
 #endif							/* LSYSCACHE_H */