Revert "Refactor CopyAttributeOut{CSV,Text}() to use a callback in COPY TO"

This reverts commit 2889fd23be, following a discussion with Andres
Freund as this callback, being called once per attribute when sending a
relation's row, can involve a lot of indirect function calls (more
attributes to deal with means more impact).  The effects of a dispatch
at this level would become more visible when improving the per-row code
execution of COPY TO, impacting future potential performance
improvements.

Discussion: https://postgr.es/m/20240206014125.qofww7ew3dx3v3uk@awork3.anarazel.de

src/backend/commands/copyto.c

@@ -54,14 +54,6 @@ typedef enum CopyDest
 	COPY_CALLBACK,				/* to callback function */
 } CopyDest;
 
-/*
- * Per-format callback to send output representation of one attribute for
- * a `string`.  `use_quote` tracks if quotes are required in the output
- * representation.
- */
-typedef void (*CopyAttributeOut) (CopyToState cstate, const char *string,
-								  bool use_quote);
-
 /*
  * This struct contains all the state variables used throughout a COPY TO
  * operation.
@@ -105,7 +97,6 @@ typedef struct CopyToStateData
 	MemoryContext copycontext;	/* per-copy execution context */
 
 	FmgrInfo   *out_functions;	/* lookup info for output functions */
-	CopyAttributeOut copy_attribute_out;	/* output representation callback */
 	MemoryContext rowcontext;	/* per-row evaluation context */
 	uint64		bytes_processed;	/* number of bytes processed so far */
 } CopyToStateData;
@@ -126,12 +117,9 @@ static const char BinarySignature[11] = "PGCOPY\n\377\r\n\0";
 static void EndCopy(CopyToState cstate);
 static void ClosePipeToProgram(CopyToState cstate);
 static void CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot);
-
-/* Callbacks for copy_attribute_out */
-static void CopyAttributeOutText(CopyToState cstate, const char *string,
-								 bool use_quote);
+static void CopyAttributeOutText(CopyToState cstate, const char *string);
 static void CopyAttributeOutCSV(CopyToState cstate, const char *string,
-								bool use_quote);
+								bool use_quote, bool single_attr);
 
 /* Low-level communications functions */
 static void SendCopyBegin(CopyToState cstate);
@@ -445,15 +433,6 @@ BeginCopyTo(ParseState *pstate,
 	/* Extract options from the statement node tree */
 	ProcessCopyOptions(pstate, &cstate->opts, false /* is_from */ , options);
 
-	/* Set output representation callback */
-	if (!cstate->opts.binary)
-	{
-		if (cstate->opts.csv_mode)
-			cstate->copy_attribute_out = CopyAttributeOutCSV;
-		else
-			cstate->copy_attribute_out = CopyAttributeOutText;
-	}
-
 	/* Process the source/target relation or query */
 	if (rel)
 	{
@@ -857,8 +836,11 @@ DoCopyTo(CopyToState cstate)
 
 				colname = NameStr(TupleDescAttr(tupDesc, attnum - 1)->attname);
 
-				/* Ignore quotes */
-				cstate->copy_attribute_out(cstate, colname, false);
+				if (cstate->opts.csv_mode)
+					CopyAttributeOutCSV(cstate, colname, false,
+										list_length(cstate->attnumlist) == 1);
+				else
+					CopyAttributeOutText(cstate, colname);
 			}
 
 			CopySendEndOfRow(cstate);
@@ -968,9 +950,12 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 			{
 				string = OutputFunctionCall(&out_functions[attnum - 1],
 											value);
-
-				cstate->copy_attribute_out(cstate, string,
-										   cstate->opts.force_quote_flags[attnum - 1]);
+				if (cstate->opts.csv_mode)
+					CopyAttributeOutCSV(cstate, string,
+										cstate->opts.force_quote_flags[attnum - 1],
+										list_length(cstate->attnumlist) == 1);
+				else
+					CopyAttributeOutText(cstate, string);
 			}
 			else
 			{
@@ -1000,8 +985,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 	} while (0)
 
 static void
-CopyAttributeOutText(CopyToState cstate, const char *string,
-					 bool use_quote)
+CopyAttributeOutText(CopyToState cstate, const char *string)
 {
 	const char *ptr;
 	const char *start;
@@ -1155,7 +1139,7 @@ CopyAttributeOutText(CopyToState cstate, const char *string,
  */
 static void
 CopyAttributeOutCSV(CopyToState cstate, const char *string,
-					bool use_quote)
+					bool use_quote, bool single_attr)
 {
 	const char *ptr;
 	const char *start;
@@ -1163,7 +1147,6 @@ CopyAttributeOutCSV(CopyToState cstate, const char *string,
 	char		delimc = cstate->opts.delim[0];
 	char		quotec = cstate->opts.quote[0];
 	char		escapec = cstate->opts.escape[0];
-	bool		single_attr = (list_length(cstate->attnumlist) == 1);
 
 	/* force quoting if it matches null_print (before conversion!) */
 	if (!use_quote && strcmp(string, cstate->opts.null_print) == 0)