Don't include genam.h from execnodes.h and relscan.h anymore.

This is the genam.h equivalent of 4c850ecec6 (which removed
heapam.h from a lot of other headers).  There's still a few header
includes of genam.h, but not from central headers anymore.

As a few headers are not indirectly included anymore, execnodes.h and
relscan.h need a few additional includes. Some of the depended on
types were replacable by using the underlying structs, but e.g. for
Snapshot in execnodes.h that'd have gotten more invasive than
reasonable in this commit.

Like the aforementioned commit 4c850ecec6, this requires adding new
genam.h includes to a number of backend files, which likely is also
required in a few external projects.

Author: Andres Freund
Discussion: https://postgr.es/m/20190114000701.y4ttcb74jpskkcfb@alap3.anarazel.de

src/backend/access/heap/heapam.c

@@ -39,6 +39,7 @@
 #include "postgres.h"
 
 #include "access/bufmask.h"
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/heapam_xlog.h"
 #include "access/hio.h"

src/backend/access/index/genam.c

@@ -19,6 +19,7 @@
 
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/relscan.h"
 #include "access/transam.h"

src/backend/bootstrap/bootstrap.c

@@ -17,6 +17,7 @@
 #include <unistd.h>
 #include <signal.h>
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/xact.h"

src/backend/catalog/dependency.c

@@ -14,6 +14,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/htup_details.h"
 #include "access/heapam.h"
 #include "access/xact.h"

src/backend/catalog/heap.c

@@ -29,6 +29,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/multixact.h"

src/backend/catalog/indexing.c

@@ -15,6 +15,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "catalog/index.h"

src/backend/catalog/objectaddress.c

@@ -15,6 +15,7 @@
 
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/sysattr.h"

src/backend/commands/analyze.c

@@ -16,6 +16,7 @@
 
 #include <math.h>
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/multixact.h"
 #include "access/sysattr.h"

src/backend/commands/constraint.c

@@ -13,6 +13,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "catalog/index.h"
 #include "commands/trigger.h"

src/backend/commands/extension.c

@@ -29,6 +29,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/sysattr.h"

src/backend/commands/matview.c

@@ -14,6 +14,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/multixact.h"

src/backend/commands/typecmds.c

@@ -31,6 +31,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/xact.h"

src/backend/executor/execCurrent.c

@@ -12,6 +12,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/relscan.h"
 #include "access/sysattr.h"
 #include "catalog/pg_type.h"

src/backend/executor/execIndexing.c

@@ -106,6 +106,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/relscan.h"
 #include "access/xact.h"
 #include "catalog/index.h"

src/backend/executor/execReplication.c

@@ -14,6 +14,7 @@
 
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/relscan.h"
 #include "access/transam.h"

src/backend/executor/nodeBitmapIndexscan.c

@@ -21,6 +21,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "executor/execdebug.h"
 #include "executor/nodeBitmapIndexscan.h"
 #include "executor/nodeIndexscan.h"

src/backend/executor/nodeIndexonlyscan.c

@@ -30,7 +30,9 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/relscan.h"
+#include "access/tupdesc.h"
 #include "access/visibilitymap.h"
 #include "executor/execdebug.h"
 #include "executor/nodeIndexonlyscan.h"

src/backend/optimizer/plan/planner.c

@@ -18,6 +18,7 @@
 #include <limits.h>
 #include <math.h>
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/parallel.h"

src/backend/utils/init/postinit.c

@@ -19,6 +19,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/session.h"

src/include/access/relscan.h

@@ -14,11 +14,12 @@
 #ifndef RELSCAN_H
 #define RELSCAN_H
 
-#include "access/genam.h"
 #include "access/htup_details.h"
 #include "access/itup.h"
-#include "access/tupdesc.h"
+#include "port/atomics.h"
+#include "storage/buf.h"
 #include "storage/spin.h"
+#include "utils/relcache.h"
 
 /*
  * Shared state for parallel heap scan.
@@ -46,9 +47,9 @@ typedef struct HeapScanDescData
 {
 	/* scan parameters */
 	Relation	rs_rd;			/* heap relation descriptor */
-	Snapshot	rs_snapshot;	/* snapshot to see */
+	struct SnapshotData *rs_snapshot;	/* snapshot to see */
 	int			rs_nkeys;		/* number of scan keys */
-	ScanKey		rs_key;			/* array of scan key descriptors */
+	struct ScanKeyData *rs_key;			/* array of scan key descriptors */
 	bool		rs_bitmapscan;	/* true if this is really a bitmap scan */
 	bool		rs_samplescan;	/* true if this is really a sample scan */
 	bool		rs_pageatatime; /* verify visibility page-at-a-time? */
@@ -88,11 +89,11 @@ typedef struct IndexScanDescData
 	/* scan parameters */
 	Relation	heapRelation;	/* heap relation descriptor, or NULL */
 	Relation	indexRelation;	/* index relation descriptor */
-	Snapshot	xs_snapshot;	/* snapshot to see */
+	struct SnapshotData *xs_snapshot;	/* snapshot to see */
 	int			numberOfKeys;	/* number of index qualifier conditions */
 	int			numberOfOrderBys;	/* number of ordering operators */
-	ScanKey		keyData;		/* array of index qualifier descriptors */
+	struct ScanKeyData *keyData;		/* array of index qualifier descriptors */
-	ScanKey		orderByData;	/* array of ordering op descriptors */
+	struct ScanKeyData *orderByData;	/* array of ordering op descriptors */
 	bool		xs_want_itup;	/* caller requests index tuples */
 	bool		xs_temp_snap;	/* unregister snapshot at scan end? */
 
@@ -112,9 +113,9 @@ typedef struct IndexScanDescData
 	 * format will be used.
 	 */
 	IndexTuple	xs_itup;		/* index tuple returned by AM */
-	TupleDesc	xs_itupdesc;	/* rowtype descriptor of xs_itup */
+	struct TupleDescData *xs_itupdesc;	/* rowtype descriptor of xs_itup */
 	HeapTuple	xs_hitup;		/* index data returned by AM, as HeapTuple */
-	TupleDesc	xs_hitupdesc;	/* rowtype descriptor of xs_hitup */
+	struct TupleDescData *xs_hitupdesc;	/* rowtype descriptor of xs_hitup */
 
 	/* xs_ctup/xs_cbuf/xs_recheck are valid after a successful index_getnext */
 	HeapTupleData xs_ctup;		/* current heap tuple, if any */
@@ -137,7 +138,7 @@ typedef struct IndexScanDescData
 	bool		xs_continue_hot;	/* T if must keep walking HOT chain */
 
 	/* parallel index scan information, in shared memory */
-	ParallelIndexScanDesc parallel_scan;
+	struct ParallelIndexScanDescData *parallel_scan;
 }			IndexScanDescData;
 
 /* Generic structure for parallel scans */
@@ -155,8 +156,8 @@ typedef struct SysScanDescData
 	Relation	heap_rel;		/* catalog being scanned */
 	Relation	irel;			/* NULL if doing heap scan */
 	struct HeapScanDescData *scan;			/* only valid in heap-scan case */
-	IndexScanDesc iscan;		/* only valid in index-scan case */
+	struct IndexScanDescData *iscan;		/* only valid in index-scan case */
-	Snapshot	snapshot;		/* snapshot to unregister at end of scan */
+	struct SnapshotData *snapshot;		/* snapshot to unregister at end of scan */
 }			SysScanDescData;
 
 #endif							/* RELSCAN_H */

src/include/executor/nodeIndexscan.h

@@ -14,6 +14,7 @@
 #ifndef NODEINDEXSCAN_H
 #define NODEINDEXSCAN_H
 
+#include "access/genam.h"
 #include "access/parallel.h"
 #include "nodes/execnodes.h"
 

src/include/nodes/execnodes.h

@@ -14,7 +14,6 @@
 #ifndef EXECNODES_H
 #define EXECNODES_H
 
-#include "access/genam.h"
 #include "access/tupconvert.h"
 #include "executor/instrument.h"
 #include "lib/pairingheap.h"
@@ -24,6 +23,7 @@
 #include "utils/queryenvironment.h"
 #include "utils/reltrigger.h"
 #include "utils/sharedtuplestore.h"
+#include "utils/snapshot.h"
 #include "utils/sortsupport.h"
 #include "utils/tuplestore.h"
 #include "utils/tuplesort.h"
@@ -1306,14 +1306,14 @@ typedef struct SampleScanState
  */
 typedef struct
 {
-	ScanKey		scan_key;		/* scankey to put value into */
+	struct ScanKeyData *scan_key;		/* scankey to put value into */
 	ExprState  *key_expr;		/* expr to evaluate to get value */
 	bool		key_toastable;	/* is expr's result a toastable datatype? */
 } IndexRuntimeKeyInfo;
 
 typedef struct
 {
-	ScanKey		scan_key;		/* scankey to put value into */
+	struct ScanKeyData *scan_key;		/* scankey to put value into */
 	ExprState  *array_expr;		/* expr to evaluate to get array value */
 	int			next_elem;		/* next array element to use */
 	int			num_elems;		/* number of elems in current array value */
@@ -1352,16 +1352,16 @@ typedef struct IndexScanState
 	ScanState	ss;				/* its first field is NodeTag */
 	ExprState  *indexqualorig;
 	List	   *indexorderbyorig;
-	ScanKey		iss_ScanKeys;
+	struct ScanKeyData *iss_ScanKeys;
 	int			iss_NumScanKeys;
-	ScanKey		iss_OrderByKeys;
+	struct ScanKeyData *iss_OrderByKeys;
 	int			iss_NumOrderByKeys;
 	IndexRuntimeKeyInfo *iss_RuntimeKeys;
 	int			iss_NumRuntimeKeys;
 	bool		iss_RuntimeKeysReady;
 	ExprContext *iss_RuntimeContext;
 	Relation	iss_RelationDesc;
-	IndexScanDesc iss_ScanDesc;
+	struct IndexScanDescData *iss_ScanDesc;
 
 	/* These are needed for re-checking ORDER BY expr ordering */
 	pairingheap *iss_ReorderQueue;
@@ -1397,16 +1397,16 @@ typedef struct IndexOnlyScanState
 {
 	ScanState	ss;				/* its first field is NodeTag */
 	ExprState  *indexqual;
-	ScanKey		ioss_ScanKeys;
+	struct ScanKeyData *ioss_ScanKeys;
 	int			ioss_NumScanKeys;
-	ScanKey		ioss_OrderByKeys;
+	struct ScanKeyData *ioss_OrderByKeys;
 	int			ioss_NumOrderByKeys;
 	IndexRuntimeKeyInfo *ioss_RuntimeKeys;
 	int			ioss_NumRuntimeKeys;
 	bool		ioss_RuntimeKeysReady;
 	ExprContext *ioss_RuntimeContext;
 	Relation	ioss_RelationDesc;
-	IndexScanDesc ioss_ScanDesc;
+	struct IndexScanDescData *ioss_ScanDesc;
 	Buffer		ioss_VMBuffer;
 	Size		ioss_PscanLen;
 } IndexOnlyScanState;
@@ -1431,7 +1431,7 @@ typedef struct BitmapIndexScanState
 {
 	ScanState	ss;				/* its first field is NodeTag */
 	TIDBitmap  *biss_result;
-	ScanKey		biss_ScanKeys;
+	struct ScanKeyData *biss_ScanKeys;
 	int			biss_NumScanKeys;
 	IndexRuntimeKeyInfo *biss_RuntimeKeys;
 	int			biss_NumRuntimeKeys;
@@ -1440,7 +1440,7 @@ typedef struct BitmapIndexScanState
 	bool		biss_RuntimeKeysReady;
 	ExprContext *biss_RuntimeContext;
 	Relation	biss_RelationDesc;
-	IndexScanDesc biss_ScanDesc;
+	struct IndexScanDescData *biss_ScanDesc;
 } BitmapIndexScanState;
 
 /* ----------------