Remove custom Constraint node read/write implementations

This is part of an effort to reduce the number of special cases in the
automatically generated node support functions.

Allegedly, only certain fields of the Constraint node are valid based
on contype.  But this has historically not been kept up to date in the
read/write functions.  The Constraint node is only used for debugging
DDL statements, so there are no strong requirements for its output,
and there is no enforcement for its correctness.  (There was no read
support before a6bc3301925.)  Commits e7a552f303c and abf46ad9c7b are
examples of where omissions were fixed.

This patch just removes the custom read/write implementations for the
Constraint node type.  Now we just output all the fields, which is a
bit more than before, but at least we don't have to maintain these
functions anymore.  Also, we lose the string representation of the
contype field, but for this marginal use case that seems tolerable.
This patch also changes the documentation of the Constraint struct to
put less emphasis on grouping fields by constraint type but rather
document for each field how it's used.

Reviewed-by: Paul Jungwirth <pj@illuminatedcomputing.com>
Discussion: https://www.postgresql.org/message-id/flat/4b27fc50-8cd6-46f5-ab20-88dbaadca645@eisentraut.org

1 files changed, 13 insertions, 25 deletions

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 476d55dd240..baa6a97c7e2 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2566,44 +2566,34 @@ typedef enum ConstrType			/* types of constraints */
 
 typedef struct Constraint
 {
-	pg_node_attr(custom_read_write)
-
 	NodeTag		type;
 	ConstrType	contype;		/* see above */
-
-	/* Fields used for most/all constraint types: */
 	char	   *conname;		/* Constraint name, or NULL if unnamed */
 	bool		deferrable;		/* DEFERRABLE? */
 	bool		initdeferred;	/* INITIALLY DEFERRED? */
-	int			location;		/* token location, or -1 if unknown */
-
-	/* Fields used for constraints with expressions (CHECK and DEFAULT): */
+	bool		skip_validation;	/* skip validation of existing rows? */
+	bool		initially_valid;	/* mark the new constraint as valid? */
 	bool		is_no_inherit;	/* is constraint non-inheritable? */
-	Node	   *raw_expr;		/* expr, as untransformed parse tree */
-	char	   *cooked_expr;	/* expr, as nodeToString representation */
+	Node	   *raw_expr;		/* CHECK or DEFAULT expression, as
+								 * untransformed parse tree */
+	char	   *cooked_expr;	/* CHECK or DEFAULT expression, as
+								 * nodeToString representation */
 	char		generated_when; /* ALWAYS or BY DEFAULT */
-
-	/* Fields used for "raw" NOT NULL constraints: */
-	int			inhcount;		/* initial inheritance count to apply */
-
-	/* Fields used for unique constraints (UNIQUE and PRIMARY KEY): */
+	int			inhcount;		/* initial inheritance count to apply, for
+								 * "raw" NOT NULL constraints */
 	bool		nulls_not_distinct; /* null treatment for UNIQUE constraints */
 	List	   *keys;			/* String nodes naming referenced key
-								 * column(s); also used for NOT NULL */
+								 * column(s); for UNIQUE/PK/NOT NULL */
 	bool		without_overlaps;	/* WITHOUT OVERLAPS specified */
 	List	   *including;		/* String nodes naming referenced nonkey
-								 * column(s) */
-
-	/* Fields used for EXCLUSION constraints: */
-	List	   *exclusions;		/* list of (IndexElem, operator name) pairs */
-
-	/* Fields used for index constraints (UNIQUE, PRIMARY KEY, EXCLUSION): */
+								 * column(s); for UNIQUE/PK */
+	List	   *exclusions;		/* list of (IndexElem, operator name) pairs;
+								 * for exclusion constraints */
 	List	   *options;		/* options from WITH clause */
 	char	   *indexname;		/* existing index to use; otherwise NULL */
 	char	   *indexspace;		/* index tablespace; NULL for default */
 	bool		reset_default_tblspc;	/* reset default_tablespace prior to
 										 * creating the index */
-	/* These could be, but currently are not, used for UNIQUE/PKEY: */
 	char	   *access_method;	/* index access method; NULL for default */
 	Node	   *where_clause;	/* partial index predicate */
 
@@ -2619,9 +2609,7 @@ typedef struct Constraint
 	Oid			old_pktable_oid;	/* pg_constraint.confrelid of my former
 									 * self */
 
-	/* Fields used for constraints that allow a NOT VALID specification */
-	bool		skip_validation;	/* skip validation of existing rows? */
-	bool		initially_valid;	/* mark the new constraint as valid? */
+	int			location;		/* token location, or -1 if unknown */
 } Constraint;
 
 /* ----------------------