0016-MergeAttributes-convert-pg_attribute-back-to-ColumnD.patch

From 0896393c4794574b5bf476fc493842297b47848a Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 22 Jun 2023 20:17:56 +0200
Subject: [PATCH 16/17] MergeAttributes: convert pg_attribute back to ColumnDef
 before comparing

MergeAttributes() has a loop to merge multiple inheritance parents
into a column column definition.  The merged-so-far definition is
stored in a ColumnDef node.  If we have to merge columns from multiple
inheritance parents (if the name matches), then we have to check
whether various column properties (type, collation, etc.) match.  The
current code extracts the pg_attribute value of the
currently-considered inheritance parent and compares it against the
merge-so-far ColumnDef value.  If the currently considered column
doesn't match any previously inherited column, we make a new ColumnDef
node from the pg_attribute information and add it to the column list.

This patch rearranges this so that we create the ColumnDef node first
in either case.  Then the code that checks the column properties for
compatibility compares ColumnDef against ColumnDef (instead of
ColumnDef against pg_attribute).  This matches the code more symmetric
and easier to follow.  Also, later in MergeAttributes(), there is a
similar but separate loop that merges the new local column definition
with the combination of the inheritance parents established in the
first loop.  That comparison is already ColumnDef-vs-ColumnDef.  With
this change, but of these can use similar looking logic.  (A future
project might be to extract these two sets of code into a common
routine that encodes all the knowledge of whether two column
definitions are compatible.  But this isn't currently straightforward
because we want to give different error messages in the two cases.)
Furthermore, by avoiding the use of Form_pg_attribute here, we make it
easier to make changes in the pg_attribute layout without having to
worry about the local needs of tablecmds.c.

Because MergeAttributes() is hugely long, it's sometimes hard to know
where in the function you are currently looking.  To help with that, I
also renamed some variables to make it clearer where you are currently
looking.  The first look is "prev" vs. "new", the second loop is "inh"
vs. "new".
---
 src/backend/commands/tablecmds.c | 179 ++++++++++++++++---------------
 1 file changed, 93 insertions(+), 86 deletions(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index bb0fb8b9af..ac7452bcff 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -2649,7 +2649,8 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 														parent_attno - 1);
 			char	   *attributeName = NameStr(attribute->attname);
 			int			exist_attno;
-			ColumnDef  *def;
+			ColumnDef  *newdef;
+			ColumnDef  *savedef;
 
 			/*
 			 * Ignore dropped columns in the parent.
@@ -2658,14 +2659,30 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 				continue;		/* leave newattmap->attnums entry as zero */
 
 			/*
-			 * Does it conflict with some previously inherited column?
+			 * Create new column definition
+			 */
+			newdef = makeColumnDef(attributeName, attribute->atttypid, attribute->atttypmod, attribute->attcollation);
+			newdef->is_not_null = attribute->attnotnull;
+			newdef->storage = attribute->attstorage;
+			newdef->generated = attribute->attgenerated;
+			if (CompressionMethodIsValid(attribute->attcompression))
+				newdef->compression =
+					pstrdup(GetCompressionMethodName(attribute->attcompression));
+
+			/*
+			 * Does it match some previously considered column from another
+			 * parent?
 			 */
 			exist_attno = findAttrByName(attributeName, inh_columns);
 			if (exist_attno > 0)
 			{
-				Oid			defTypeId;
-				int32		deftypmod;
-				Oid			defCollId;
+				ColumnDef  *prevdef;
+				Oid			prevtypeid,
+							newtypeid;
+				int32		prevtypmod,
+							newtypmod;
+				Oid			prevcollid,
+							newcollid;
 
 				/*
 				 * Yes, try to merge the two column definitions.
@@ -2673,78 +2690,71 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 				ereport(NOTICE,
 						(errmsg("merging multiple inherited definitions of column \"%s\"",
 								attributeName)));
-				def = (ColumnDef *) list_nth(inh_columns, exist_attno - 1);
+				prevdef = list_nth_node(ColumnDef, inh_columns, exist_attno - 1);
 
 				/*
 				 * Must have the same type and typmod
 				 */
-				typenameTypeIdAndMod(NULL, def->typeName, &defTypeId, &deftypmod);
-				if (defTypeId != attribute->atttypid ||
-					deftypmod != attribute->atttypmod)
+				typenameTypeIdAndMod(NULL, prevdef->typeName, &prevtypeid, &prevtypmod);
+				typenameTypeIdAndMod(NULL, newdef->typeName, &newtypeid, &newtypmod);
+				if (prevtypeid != newtypeid || prevtypmod != newtypmod)
 					ereport(ERROR,
 							(errcode(ERRCODE_DATATYPE_MISMATCH),
 							 errmsg("inherited column \"%s\" has a type conflict",
 									attributeName),
 							 errdetail("%s versus %s",
-									   format_type_with_typemod(defTypeId,
-																deftypmod),
-									   format_type_with_typemod(attribute->atttypid,
-																attribute->atttypmod))));
+									   format_type_with_typemod(prevtypeid, prevtypmod),
+									   format_type_with_typemod(newtypeid, newtypmod))));
 
 				/*
 				 * Must have the same collation
 				 */
-				defCollId = GetColumnDefCollation(NULL, def, defTypeId);
-				if (defCollId != attribute->attcollation)
+				prevcollid = GetColumnDefCollation(NULL, prevdef, prevtypeid);
+				newcollid = GetColumnDefCollation(NULL, newdef, newtypeid);
+				if (prevcollid != newcollid)
 					ereport(ERROR,
 							(errcode(ERRCODE_COLLATION_MISMATCH),
 							 errmsg("inherited column \"%s\" has a collation conflict",
 									attributeName),
 							 errdetail("\"%s\" versus \"%s\"",
-									   get_collation_name(defCollId),
-									   get_collation_name(attribute->attcollation))));
+									   get_collation_name(prevcollid),
+									   get_collation_name(newcollid))));
 
 				/*
 				 * Copy/check storage parameter
 				 */
-				if (def->storage == 0)
-					def->storage = attribute->attstorage;
-				else if (def->storage != attribute->attstorage)
+				if (prevdef->storage == 0)
+					prevdef->storage = newdef->storage;
+				else if (prevdef->storage != newdef->storage)
 					ereport(ERROR,
 							(errcode(ERRCODE_DATATYPE_MISMATCH),
 							 errmsg("inherited column \"%s\" has a storage parameter conflict",
 									attributeName),
 							 errdetail("%s versus %s",
-									   storage_name(def->storage),
-									   storage_name(attribute->attstorage))));
+									   storage_name(prevdef->storage),
+									   storage_name(newdef->storage))));
 
 				/*
 				 * Copy/check compression parameter
 				 */
-				if (CompressionMethodIsValid(attribute->attcompression))
-				{
-					const char *compression =
-						GetCompressionMethodName(attribute->attcompression);
-
-					if (def->compression == NULL)
-						def->compression = pstrdup(compression);
-					else if (strcmp(def->compression, compression) != 0)
-						ereport(ERROR,
-								(errcode(ERRCODE_DATATYPE_MISMATCH),
-								 errmsg("column \"%s\" has a compression method conflict",
-										attributeName),
-								 errdetail("%s versus %s", def->compression, compression)));
-				}
+				if (prevdef->compression == NULL)
+					prevdef->compression = newdef->compression;
+				else if (strcmp(prevdef->compression, newdef->compression) != 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_DATATYPE_MISMATCH),
+							 errmsg("column \"%s\" has a compression method conflict",
+									attributeName),
+							 errdetail("%s versus %s", prevdef->compression, newdef->compression)));
 
 				/*
 				 * Merge of NOT NULL constraints = OR 'em together
 				 */
-				def->is_not_null |= attribute->attnotnull;
+				prevdef->is_not_null |= newdef->is_not_null;
 
 				/*
 				 * Check for GENERATED conflicts
 				 */
-				if (def->generated != attribute->attgenerated)
+				if (prevdef->generated != newdef->generated)
 					ereport(ERROR,
 							(errcode(ERRCODE_DATATYPE_MISMATCH),
 							 errmsg("inherited column \"%s\" has a generation conflict",
@@ -2754,30 +2764,29 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 				 * Default and other constraints are handled below
 				 */
 
-				def->inhcount++;
-				if (def->inhcount < 0)
+				prevdef->inhcount++;
+				if (prevdef->inhcount < 0)
 					ereport(ERROR,
 							errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 							errmsg("too many inheritance parents"));
 
 				newattmap->attnums[parent_attno - 1] = exist_attno;
+
+				/* remember for default processing below */
+				savedef = prevdef;
 			}
 			else
 			{
 				/*
 				 * No, create a new inherited column
 				 */
-				def = makeColumnDef(attributeName, attribute->atttypid, attribute->atttypmod, attribute->attcollation);
-				def->inhcount = 1;
-				def->is_local = false;
-				def->is_not_null = attribute->attnotnull;
-				def->storage = attribute->attstorage;
-				def->generated = attribute->attgenerated;
-				if (CompressionMethodIsValid(attribute->attcompression))
-					def->compression =
-						pstrdup(GetCompressionMethodName(attribute->attcompression));
-				inh_columns = lappend(inh_columns, def);
+				newdef->inhcount = 1;
+				newdef->is_local = false;
+				inh_columns = lappend(inh_columns, newdef);
 				newattmap->attnums[parent_attno - 1] = ++child_attno;
+
+				/* remember for default processing below */
+				savedef = newdef;
 			}
 
 			/*
@@ -2799,7 +2808,7 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 				 * all the inherited default expressions for the moment.
 				 */
 				inherited_defaults = lappend(inherited_defaults, this_default);
-				cols_with_defaults = lappend(cols_with_defaults, def);
+				cols_with_defaults = lappend(cols_with_defaults, savedef);
 			}
 		}
 
@@ -2920,17 +2929,17 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 			newcol_attno++;
 
 			/*
-			 * Does it conflict with some previously inherited column?
+			 * Does it match some inherited column?
 			 */
 			exist_attno = findAttrByName(attributeName, inh_columns);
 			if (exist_attno > 0)
 			{
-				ColumnDef  *def;
-				Oid			defTypeId,
-							newTypeId;
-				int32		deftypmod,
+				ColumnDef  *inhdef;
+				Oid			inhtypeid,
+							newtypeid;
+				int32		inhtypmod,
 							newtypmod;
-				Oid			defcollid,
+				Oid			inhcollid,
 							newcollid;
 
 				/*
@@ -2950,77 +2959,75 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 					ereport(NOTICE,
 							(errmsg("moving and merging column \"%s\" with inherited definition", attributeName),
 							 errdetail("User-specified column moved to the position of the inherited column.")));
-				def = (ColumnDef *) list_nth(inh_columns, exist_attno - 1);
+				inhdef = list_nth_node(ColumnDef, inh_columns, exist_attno - 1);
 
 				/*
 				 * Must have the same type and typmod
 				 */
-				typenameTypeIdAndMod(NULL, def->typeName, &defTypeId, &deftypmod);
-				typenameTypeIdAndMod(NULL, newdef->typeName, &newTypeId, &newtypmod);
-				if (defTypeId != newTypeId || deftypmod != newtypmod)
+				typenameTypeIdAndMod(NULL, inhdef->typeName, &inhtypeid, &inhtypmod);
+				typenameTypeIdAndMod(NULL, newdef->typeName, &newtypeid, &newtypmod);
+				if (inhtypeid != newtypeid || inhtypmod != newtypmod)
 					ereport(ERROR,
 							(errcode(ERRCODE_DATATYPE_MISMATCH),
 							 errmsg("column \"%s\" has a type conflict",
 									attributeName),
 							 errdetail("%s versus %s",
-									   format_type_with_typemod(defTypeId,
-																deftypmod),
-									   format_type_with_typemod(newTypeId,
-																newtypmod))));
+									   format_type_with_typemod(inhtypeid, inhtypmod),
+									   format_type_with_typemod(newtypeid, newtypmod))));
 
 				/*
 				 * Must have the same collation
 				 */
-				defcollid = GetColumnDefCollation(NULL, def, defTypeId);
-				newcollid = GetColumnDefCollation(NULL, newdef, newTypeId);
-				if (defcollid != newcollid)
+				inhcollid = GetColumnDefCollation(NULL, inhdef, inhtypeid);
+				newcollid = GetColumnDefCollation(NULL, newdef, newtypeid);
+				if (inhcollid != newcollid)
 					ereport(ERROR,
 							(errcode(ERRCODE_COLLATION_MISMATCH),
 							 errmsg("column \"%s\" has a collation conflict",
 									attributeName),
 							 errdetail("\"%s\" versus \"%s\"",
-									   get_collation_name(defcollid),
+									   get_collation_name(inhcollid),
 									   get_collation_name(newcollid))));
 
 				/*
 				 * Identity is never inherited.  The new column can have an
 				 * identity definition, so we always just take that one.
 				 */
-				def->identity = newdef->identity;
+				inhdef->identity = newdef->identity;
 
 				/*
 				 * Copy storage parameter
 				 */
-				if (def->storage == 0)
-					def->storage = newdef->storage;
-				else if (newdef->storage != 0 && def->storage != newdef->storage)
+				if (inhdef->storage == 0)
+					inhdef->storage = newdef->storage;
+				else if (newdef->storage != 0 && inhdef->storage != newdef->storage)
 					ereport(ERROR,
 							(errcode(ERRCODE_DATATYPE_MISMATCH),
 							 errmsg("column \"%s\" has a storage parameter conflict",
 									attributeName),
 							 errdetail("%s versus %s",
-									   storage_name(def->storage),
+									   storage_name(inhdef->storage),
 									   storage_name(newdef->storage))));
 
 				/*
 				 * Copy compression parameter
 				 */
-				if (def->compression == NULL)
-					def->compression = newdef->compression;
+				if (inhdef->compression == NULL)
+					inhdef->compression = newdef->compression;
 				else if (newdef->compression != NULL)
 				{
-					if (strcmp(def->compression, newdef->compression) != 0)
+					if (strcmp(inhdef->compression, newdef->compression) != 0)
 						ereport(ERROR,
 								(errcode(ERRCODE_DATATYPE_MISMATCH),
 								 errmsg("column \"%s\" has a compression method conflict",
 										attributeName),
-								 errdetail("%s versus %s", def->compression, newdef->compression)));
+								 errdetail("%s versus %s", inhdef->compression, newdef->compression)));
 				}
 
 				/*
 				 * Merge of NOT NULL constraints = OR 'em together
 				 */
-				def->is_not_null |= newdef->is_not_null;
+				inhdef->is_not_null |= newdef->is_not_null;
 
 				/*
 				 * Check for conflicts related to generated columns.
@@ -3037,18 +3044,18 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 				 * it results in being able to override the generation
 				 * expression via UPDATEs through the parent.)
 				 */
-				if (def->generated)
+				if (inhdef->generated)
 				{
 					if (newdef->raw_default && !newdef->generated)
 						ereport(ERROR,
 								(errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
 								 errmsg("column \"%s\" inherits from generated column but specifies default",
-										def->colname)));
+										inhdef->colname)));
 					if (newdef->identity)
 						ereport(ERROR,
 								(errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
 								 errmsg("column \"%s\" inherits from generated column but specifies identity",
-										def->colname)));
+										inhdef->colname)));
 				}
 				else
 				{
@@ -3056,7 +3063,7 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 						ereport(ERROR,
 								(errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
 								 errmsg("child column \"%s\" specifies generation expression",
-										def->colname),
+										inhdef->colname),
 								 errhint("A child table column cannot be generated unless its parent column is.")));
 				}
 
@@ -3065,12 +3072,12 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 				 */
 				if (newdef->raw_default != NULL)
 				{
-					def->raw_default = newdef->raw_default;
-					def->cooked_default = newdef->cooked_default;
+					inhdef->raw_default = newdef->raw_default;
+					inhdef->cooked_default = newdef->cooked_default;
 				}
 
 				/* Mark the column as locally defined */
-				def->is_local = true;
+				inhdef->is_local = true;
 			}
 			else
 			{
-- 
2.41.0