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Improve implementation of CRE-stack-flattening in map_variable_attnos().

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I (tgl) objected to the obscure implementation introduced in commit
1c497fa72.  This one seems a bit less action-at-a-distance-y, at the
price of repeating a few lines of code.

Improve the comments about what the function is doing, too.

Amit Khandekar, whacked around a bit more by me

Discussion: https://postgr.es/m/CAJ3gD9egYTyHUH0nTMxm8-1m3RvdqEbaTyGC-CUNtYf7tKNDaQ@mail.gmail.com
This commit is contained in:
Tom Lane
2017-10-13 13:43:55 -04:00
parent 5229db6c6f
commit 73937119bf
1 changed files with 53 additions and 44 deletions
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97
src/backend/rewrite/rewriteManip.c
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@ -1203,9 +1203,11 @@ replace_rte_variables_mutator(Node *node,
* appear in the expression. * appear in the expression.
* *
* If the expression tree contains a whole-row Var for the target RTE, * If the expression tree contains a whole-row Var for the target RTE,
* *found_whole_row is returned as TRUE. In addition, if to_rowtype is * *found_whole_row is set to TRUE. In addition, if to_rowtype is
* not InvalidOid, we modify the Var's vartype and insert a ConvertRowTypeExpr * not InvalidOid, we replace the Var with a Var of that vartype, inserting
* to map back to the orignal rowtype. Callers that don't provide to_rowtype * a ConvertRowTypeExpr to map back to the rowtype expected by the expression.
* (Therefore, to_rowtype had better be a child rowtype of the rowtype of the
* RTE we're changing references to.) Callers that don't provide to_rowtype
* should report an error if *found_row_type is true; we don't do that here * should report an error if *found_row_type is true; we don't do that here
* because we don't know exactly what wording for the error message would * because we don't know exactly what wording for the error message would
* be most appropriate. The caller will be aware of the context. * be most appropriate. The caller will be aware of the context.
@ -1221,10 +1223,8 @@ typedef struct
int sublevels_up; /* (current) nesting depth */ int sublevels_up; /* (current) nesting depth */
const AttrNumber *attno_map; /* map array for user attnos */ const AttrNumber *attno_map; /* map array for user attnos */
int map_length; /* number of entries in attno_map[] */ int map_length; /* number of entries in attno_map[] */
/* Target type when converting whole-row vars */ Oid to_rowtype; /* change whole-row Vars to this type */
Oid to_rowtype;
bool *found_whole_row; /* output flag */ bool *found_whole_row; /* output flag */
bool coerced_var; /* var is under ConvertRowTypeExpr */
} map_variable_attnos_context; } map_variable_attnos_context;
static Node * static Node *
@ -1244,7 +1244,8 @@ map_variable_attnos_mutator(Node *node,
Var *newvar = (Var *) palloc(sizeof(Var)); Var *newvar = (Var *) palloc(sizeof(Var));
int attno = var->varattno; int attno = var->varattno;
*newvar = *var; *newvar = *var; /* initially copy all fields of the Var */
if (attno > 0) if (attno > 0)
{ {
/* user-defined column, replace attno */ /* user-defined column, replace attno */
@ -1259,39 +1260,29 @@ map_variable_attnos_mutator(Node *node,
/* whole-row variable, warn caller */ /* whole-row variable, warn caller */
*(context->found_whole_row) = true; *(context->found_whole_row) = true;
/* If the callers expects us to convert the same, do so. */ /* If the caller expects us to convert the Var, do so. */
if (OidIsValid(context->to_rowtype)) if (OidIsValid(context->to_rowtype) &&
context->to_rowtype != var->vartype)
{ {
/* No support for RECORDOID. */ ConvertRowtypeExpr *r;
/* This certainly won't work for a RECORD variable. */
Assert(var->vartype != RECORDOID); Assert(var->vartype != RECORDOID);
/* Don't convert unless necessary. */ /* Var itself is changed to the requested type. */
if (context->to_rowtype != var->vartype) newvar->vartype = context->to_rowtype;
{
/* Var itself is converted to the requested type. */
newvar->vartype = context->to_rowtype;
/* /*
* If this var is already under a ConvertRowtypeExpr, * Add a conversion node on top to convert back to the
* we don't have to add another one. * original type expected by the expression.
*/ */
if (!context->coerced_var) r = makeNode(ConvertRowtypeExpr);
{ r->arg = (Expr *) newvar;
ConvertRowtypeExpr *r; r->resulttype = var->vartype;
r->convertformat = COERCE_IMPLICIT_CAST;
r->location = -1;
/* return (Node *) r;
* And a conversion node on top to convert back to
* the original type.
*/
r = makeNode(ConvertRowtypeExpr);
r->arg = (Expr *) newvar;
r->resulttype = var->vartype;
r->convertformat = COERCE_IMPLICIT_CAST;
r->location = -1;
return (Node *) r;
}
}
} }
} }
return (Node *) newvar; return (Node *) newvar;
@ -1301,24 +1292,43 @@ map_variable_attnos_mutator(Node *node,
else if (IsA(node, ConvertRowtypeExpr)) else if (IsA(node, ConvertRowtypeExpr))
{ {
ConvertRowtypeExpr *r = (ConvertRowtypeExpr *) node; ConvertRowtypeExpr *r = (ConvertRowtypeExpr *) node;
Var *var = (Var *) r->arg;
/* /*
* If this is coercing a var (which is typical), convert only the var, * If this is coercing a whole-row Var that we need to convert, then
* as against adding another ConvertRowtypeExpr over it. * just convert the Var without adding an extra ConvertRowtypeExpr.
* Effectively we're simplifying var::parenttype::grandparenttype into
* just var::grandparenttype. This avoids building stacks of CREs if
* this function is applied repeatedly.
*/ */
if (IsA(r->arg, Var)) if (IsA(var, Var) &&
var->varno == context->target_varno &&
var->varlevelsup == context->sublevels_up &&
var->varattno == 0 &&
OidIsValid(context->to_rowtype) &&
context->to_rowtype != var->vartype)
{ {
ConvertRowtypeExpr *newnode; ConvertRowtypeExpr *newnode;
Var *newvar = (Var *) palloc(sizeof(Var));
/* whole-row variable, warn caller */
*(context->found_whole_row) = true;
*newvar = *var; /* initially copy all fields of the Var */
/* This certainly won't work for a RECORD variable. */
Assert(var->vartype != RECORDOID);
/* Var itself is changed to the requested type. */
newvar->vartype = context->to_rowtype;
newnode = (ConvertRowtypeExpr *) palloc(sizeof(ConvertRowtypeExpr)); newnode = (ConvertRowtypeExpr *) palloc(sizeof(ConvertRowtypeExpr));
*newnode = *r; *newnode = *r; /* initially copy all fields of the CRE */
context->coerced_var = true; newnode->arg = (Expr *) newvar;
newnode->arg = (Expr *) map_variable_attnos_mutator((Node *) r->arg, context);
context->coerced_var = false;
return (Node *) newnode; return (Node *) newnode;
} }
/* Else fall through the expression tree mutator */ /* otherwise fall through to process the expression normally */
} }
else if (IsA(node, Query)) else if (IsA(node, Query))
{ {
@ -1351,7 +1361,6 @@ map_variable_attnos(Node *node,
context.map_length = map_length; context.map_length = map_length;
context.to_rowtype = to_rowtype; context.to_rowtype = to_rowtype;
context.found_whole_row = found_whole_row; context.found_whole_row = found_whole_row;
context.coerced_var = false;
*found_whole_row = false; *found_whole_row = false;