Extend the parser location infrastructure to include a location field in

most node types used in expression trees (both before and after parse
analysis).  This allows us to place an error cursor in many situations
where we formerly could not, because the information wasn't available
beyond the very first level of parse analysis.  There's a fair amount
of work still to be done to persuade individual ereport() calls to actually
include an error location, but this gets the initdb-forcing part of the
work out of the way; and the situation is already markedly better than
before for complaints about unimplementable implicit casts, such as
CASE and UNION constructs with incompatible alternative data types.
Per my proposal of a few days ago.

src/include/nodes/primnodes.h

@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/primnodes.h,v 1.139 2008/08/22 00:16:04 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/primnodes.h,v 1.140 2008/08/28 23:09:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -138,14 +138,12 @@ typedef struct Var
 								 * all */
 	Oid			vartype;		/* pg_type OID for the type of this var */
 	int32		vartypmod;		/* pg_attribute typmod value */
-	Index		varlevelsup;
-
-	/*
-	 * for subquery variables referencing outer relations; 0 in a normal var,
-	 * >0 means N levels up
-	 */
+	Index		varlevelsup;	/* for subquery variables referencing outer
+								 * relations; 0 in a normal var, >0 means N
+								 * levels up */
 	Index		varnoold;		/* original value of varno, for debugging */
 	AttrNumber	varoattno;		/* original value of varattno */
+	int			location;		/* token location, or -1 if unknown */
 } Var;
 
 /*
@@ -164,6 +162,7 @@ typedef struct Const
 								 * If true, then all the information is stored
 								 * in the Datum. If false, then the Datum
 								 * contains a pointer to the information. */
+	int			location;		/* token location, or -1 if unknown */
 } Const;
 
 /* ----------------
@@ -204,6 +203,7 @@ typedef struct Param
 	int			paramid;		/* numeric ID for parameter */
 	Oid			paramtype;		/* pg_type OID of parameter's datatype */
 	int32		paramtypmod;	/* typmod value, if known */
+	int			location;		/* token location, or -1 if unknown */
 } Param;
 
 /*
@@ -218,6 +218,7 @@ typedef struct Aggref
 	Index		agglevelsup;	/* > 0 if agg belongs to outer query */
 	bool		aggstar;		/* TRUE if argument list was really '*' */
 	bool		aggdistinct;	/* TRUE if it's agg(DISTINCT ...) */
+	int			location;		/* token location, or -1 if unknown */
 } Aggref;
 
 /* ----------------
@@ -293,6 +294,7 @@ typedef struct FuncExpr
 	bool		funcretset;		/* true if function returns set */
 	CoercionForm funcformat;	/* how to display this function call */
 	List	   *args;			/* arguments to the function */
+	int			location;		/* token location, or -1 if unknown */
 } FuncExpr;
 
 /*
@@ -312,6 +314,7 @@ typedef struct OpExpr
 	Oid			opresulttype;	/* PG_TYPE OID of result value */
 	bool		opretset;		/* true if operator returns set */
 	List	   *args;			/* arguments to the operator (1 or 2) */
+	int			location;		/* token location, or -1 if unknown */
 } OpExpr;
 
 /*
@@ -343,6 +346,7 @@ typedef struct ScalarArrayOpExpr
 	Oid			opfuncid;		/* PG_PROC OID of underlying function */
 	bool		useOr;			/* true for ANY, false for ALL */
 	List	   *args;			/* the scalar and array operands */
+	int			location;		/* token location, or -1 if unknown */
 } ScalarArrayOpExpr;
 
 /*
@@ -350,9 +354,11 @@ typedef struct ScalarArrayOpExpr
  *
  * Notice the arguments are given as a List.  For NOT, of course the list
  * must always have exactly one element.  For AND and OR, the executor can
- * handle any number of arguments.	The parser treats AND and OR as binary
- * and so it only produces two-element lists, but the optimizer will flatten
- * trees of AND and OR nodes to produce longer lists when possible.
+ * handle any number of arguments.  The parser generally treats AND and OR
+ * as binary and so it typically only produces two-element lists, but the
+ * optimizer will flatten trees of AND and OR nodes to produce longer lists
+ * when possible.  There are also a few special cases where more arguments
+ * can appear before optimization.
  */
 typedef enum BoolExprType
 {
@@ -364,6 +370,7 @@ typedef struct BoolExpr
 	Expr		xpr;
 	BoolExprType boolop;
 	List	   *args;			/* arguments to this expression */
+	int			location;		/* token location, or -1 if unknown */
 } BoolExpr;
 
 /*
@@ -423,6 +430,7 @@ typedef struct SubLink
 	Node	   *testexpr;		/* outer-query test for ALL/ANY/ROWCOMPARE */
 	List	   *operName;		/* originally specified operator name */
 	Node	   *subselect;		/* subselect as Query* or parsetree */
+	int			location;		/* token location, or -1 if unknown */
 } SubLink;
 
 /*
@@ -570,6 +578,7 @@ typedef struct RelabelType
 	Oid			resulttype;		/* output type of coercion expression */
 	int32		resulttypmod;	/* output typmod (usually -1) */
 	CoercionForm relabelformat; /* how to display this node */
+	int			location;		/* token location, or -1 if unknown */
 } RelabelType;
 
 /* ----------------
@@ -588,6 +597,7 @@ typedef struct CoerceViaIO
 	Oid			resulttype;		/* output type of coercion */
 	/* output typmod is not stored, but is presumed -1 */
 	CoercionForm coerceformat;	/* how to display this node */
+	int			location;		/* token location, or -1 if unknown */
 } CoerceViaIO;
 
 /* ----------------
@@ -611,6 +621,7 @@ typedef struct ArrayCoerceExpr
 	int32		resulttypmod;	/* output typmod (also element typmod) */
 	bool		isExplicit;		/* conversion semantics flag to pass to func */
 	CoercionForm coerceformat;	/* how to display this node */
+	int			location;		/* token location, or -1 if unknown */
 } ArrayCoerceExpr;
 
 /* ----------------
@@ -632,6 +643,7 @@ typedef struct ConvertRowtypeExpr
 	Oid			resulttype;		/* output type (always a composite type) */
 	/* result typmod is not stored, but must be -1; see RowExpr comments */
 	CoercionForm convertformat; /* how to display this node */
+	int			location;		/* token location, or -1 if unknown */
 } ConvertRowtypeExpr;
 
 /*----------
@@ -663,6 +675,7 @@ typedef struct CaseExpr
 	Expr	   *arg;			/* implicit equality comparison argument */
 	List	   *args;			/* the arguments (list of WHEN clauses) */
 	Expr	   *defresult;		/* the default result (ELSE clause) */
+	int			location;		/* token location, or -1 if unknown */
 } CaseExpr;
 
 /*
@@ -673,6 +686,7 @@ typedef struct CaseWhen
 	Expr		xpr;
 	Expr	   *expr;			/* condition expression */
 	Expr	   *result;			/* substitution result */
+	int			location;		/* token location, or -1 if unknown */
 } CaseWhen;
 
 /*
@@ -705,6 +719,7 @@ typedef struct ArrayExpr
 	Oid			element_typeid; /* common type of array elements */
 	List	   *elements;		/* the array elements or sub-arrays */
 	bool		multidims;		/* true if elements are sub-arrays */
+	int			location;		/* token location, or -1 if unknown */
 } ArrayExpr;
 
 /*
@@ -733,6 +748,7 @@ typedef struct RowExpr
 	 * parsetrees.	We must assume typmod -1 for a RowExpr node.
 	 */
 	CoercionForm row_format;	/* how to display this node */
+	int			location;		/* token location, or -1 if unknown */
 } RowExpr;
 
 /*
@@ -778,6 +794,7 @@ typedef struct CoalesceExpr
 	Expr		xpr;
 	Oid			coalescetype;	/* type of expression result */
 	List	   *args;			/* the arguments */
+	int			location;		/* token location, or -1 if unknown */
 } CoalesceExpr;
 
 /*
@@ -795,6 +812,7 @@ typedef struct MinMaxExpr
 	Oid			minmaxtype;		/* common type of arguments and result */
 	MinMaxOp	op;				/* function to execute */
 	List	   *args;			/* the arguments */
+	int			location;		/* token location, or -1 if unknown */
 } MinMaxExpr;
 
 /*
@@ -833,6 +851,7 @@ typedef struct XmlExpr
 	XmlOptionType xmloption;	/* DOCUMENT or CONTENT */
 	Oid			type;			/* target type for XMLSERIALIZE */
 	int32		typmod;
+	int			location;		/* token location, or -1 if unknown */
 } XmlExpr;
 
 /*
@@ -905,6 +924,7 @@ typedef struct CoerceToDomain
 	Oid			resulttype;		/* domain type ID (result type) */
 	int32		resulttypmod;	/* output typmod (currently always -1) */
 	CoercionForm coercionformat;	/* how to display this node */
+	int			location;		/* token location, or -1 if unknown */
 } CoerceToDomain;
 
 /*
@@ -921,6 +941,7 @@ typedef struct CoerceToDomainValue
 	Expr		xpr;
 	Oid			typeId;			/* type for substituted value */
 	int32		typeMod;		/* typemod for substituted value */
+	int			location;		/* token location, or -1 if unknown */
 } CoerceToDomainValue;
 
 /*
@@ -935,6 +956,7 @@ typedef struct SetToDefault
 	Expr		xpr;
 	Oid			typeId;			/* type for substituted value */
 	int32		typeMod;		/* typemod for substituted value */
+	int			location;		/* token location, or -1 if unknown */
 } SetToDefault;
 
 /*