Avoid including explain.h in explain_format.h and explain_dr.h

As per a suggestion from Tom Lane, we do this by declaring "struct
ExplainState" here and refer to that rather than "ExplainState".

Also per Tom, CreateExplainSerializeDestReceiver was still defined
in explain.h in addition to explain_dr.h. Remove leftover prototype.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: http://postgr.es/m/CA+TgmoYtaad3i21V0jqua-fbr+CR0ix6uBvEX8_s6BG96abd=g@mail.gmail.com

src/backend/commands/explain_dr.c

@@ -13,6 +13,7 @@
  */
 #include "postgres.h"
 
+#include "commands/explain.h"
 #include "commands/explain_dr.h"
 #include "libpq/pqformat.h"
 #include "libpq/protocol.h"

src/backend/tcop/dest.c

@@ -33,7 +33,7 @@
 #include "access/xact.h"
 #include "commands/copy.h"
 #include "commands/createas.h"
-#include "commands/explain.h"
+#include "commands/explain_dr.h"
 #include "commands/matview.h"
 #include "executor/functions.h"
 #include "executor/tqueue.h"

src/include/commands/explain.h

@@ -120,6 +120,4 @@ extern void ExplainPrintJITSummary(ExplainState *es, QueryDesc *queryDesc);
 extern void ExplainQueryText(ExplainState *es, QueryDesc *queryDesc);
 extern void ExplainQueryParameters(ExplainState *es, ParamListInfo params, int maxlen);
 
-extern DestReceiver *CreateExplainSerializeDestReceiver(ExplainState *es);
-
 #endif							/* EXPLAIN_H */

src/include/commands/explain_dr.h

@@ -13,8 +13,10 @@
 #ifndef EXPLAIN_DR_H
 #define EXPLAIN_DR_H
 
-#include "commands/explain.h"
 #include "executor/instrument.h"
+#include "tcop/dest.h"
+
+struct ExplainState;			/* avoid including explain.h here */
 
 /* Instrumentation data for EXPLAIN's SERIALIZE option */
 typedef struct SerializeMetrics
@@ -24,7 +26,7 @@ typedef struct SerializeMetrics
 	BufferUsage bufferUsage;	/* buffers accessed during serialization */
 } SerializeMetrics;
 
-extern DestReceiver *CreateExplainSerializeDestReceiver(ExplainState *es);
+extern DestReceiver *CreateExplainSerializeDestReceiver(struct ExplainState *es);
 extern SerializeMetrics GetSerializationMetrics(DestReceiver *dest);
 
 #endif

src/include/commands/explain_format.h

@@ -13,40 +13,46 @@
 #ifndef EXPLAIN_FORMAT_H
 #define EXPLAIN_FORMAT_H
 
-#include "commands/explain.h"
+#include "nodes/pg_list.h"
+
+struct ExplainState;			/* avoid including explain.h here */
 
 extern void ExplainPropertyList(const char *qlabel, List *data,
-								ExplainState *es);
+								struct ExplainState *es);
 extern void ExplainPropertyListNested(const char *qlabel, List *data,
-									  ExplainState *es);
+									  struct ExplainState *es);
 extern void ExplainPropertyText(const char *qlabel, const char *value,
-								ExplainState *es);
+								struct ExplainState *es);
 extern void ExplainPropertyInteger(const char *qlabel, const char *unit,
-								   int64 value, ExplainState *es);
+								   int64 value, struct ExplainState *es);
 extern void ExplainPropertyUInteger(const char *qlabel, const char *unit,
-									uint64 value, ExplainState *es);
+									uint64 value, struct ExplainState *es);
 extern void ExplainPropertyFloat(const char *qlabel, const char *unit,
-								 double value, int ndigits, ExplainState *es);
+								 double value, int ndigits,
+								 struct ExplainState *es);
 extern void ExplainPropertyBool(const char *qlabel, bool value,
-								ExplainState *es);
+								struct ExplainState *es);
 
 extern void ExplainOpenGroup(const char *objtype, const char *labelname,
-							 bool labeled, ExplainState *es);
+							 bool labeled, struct ExplainState *es);
 extern void ExplainCloseGroup(const char *objtype, const char *labelname,
-							  bool labeled, ExplainState *es);
+							  bool labeled, struct ExplainState *es);
 
 extern void ExplainOpenSetAsideGroup(const char *objtype, const char *labelname,
-									 bool labeled, int depth, ExplainState *es);
-extern void ExplainSaveGroup(ExplainState *es, int depth, int *state_save);
-extern void ExplainRestoreGroup(ExplainState *es, int depth, int *state_save);
+									 bool labeled, int depth,
+									 struct ExplainState *es);
+extern void ExplainSaveGroup(struct ExplainState *es, int depth,
+							 int *state_save);
+extern void ExplainRestoreGroup(struct ExplainState *es, int depth,
+								int *state_save);
 
 extern void ExplainDummyGroup(const char *objtype, const char *labelname,
-							  ExplainState *es);
+							  struct ExplainState *es);
 
-extern void ExplainBeginOutput(ExplainState *es);
-extern void ExplainEndOutput(ExplainState *es);
-extern void ExplainSeparatePlans(ExplainState *es);
+extern void ExplainBeginOutput(struct ExplainState *es);
+extern void ExplainEndOutput(struct ExplainState *es);
+extern void ExplainSeparatePlans(struct ExplainState *es);
 
-extern void ExplainIndentText(ExplainState *es);
+extern void ExplainIndentText(struct ExplainState *es);
 
 #endif