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Commit 5bcab11

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Add castNode(type, ptr) for safe casting between NodeTag based types.
The new function allows to cast from one NodeTag based type to another, while asserting that the conversion is valid. This replaces the common pattern of doing a cast and a Assert(IsA(ptr, type)) close-by. As this seems likely to be used pervasively, we decided to backpatch this change the addition of this macro. Otherwise backpatched fixes are more likely not to work on back-branches. On branches before 9.6, where we do not yet rely on inline functions being available, the type assertion is only performed if PG_USE_INLINE support is detected. The cast obviously is performed regardless. For the benefit of verifying the macro compiles in the back-branches, this commit contains a single use of the new macro. On master, a somewhat larger conversion will be committed separately. Author: Peter Eisentraut and Andres Freund Reviewed-By: Tom Lane Discussion: https://postgr.es/m/c5d387d9-3440-f5e0-f9d4-71d53b9fbe52@2ndquadrant.com Backpatch: 9.2-
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lines changed

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+21
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src/backend/tcop/postgres.c

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@@ -846,7 +846,7 @@ pg_plan_queries(List *querytrees, int cursorOptions, ParamListInfo boundParams)
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foreach(query_list, querytrees)
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{
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Query *query = (Query *) lfirst(query_list);
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Query *query = castNode(Query, lfirst(query_list));
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PlannedStmt *stmt;
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if (query->commandType == CMD_UTILITY)

src/include/nodes/nodes.h

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Original file line numberDiff line numberDiff line change
@@ -558,6 +558,26 @@ extern PGDLLIMPORT Node *newNodeMacroHolder;
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#define IsA(nodeptr,_type_) (nodeTag(nodeptr) == T_##_type_)
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/*
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* castNode(type, ptr) casts ptr to type and, if cassert is enabled, verifies
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* that the the c actually has the appropriate type (using it's nodeTag()).
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*
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* Use an inline function when assertions are enabled, to avoid multiple
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* evaluations of the ptr argument (which could e.g. be a function call).
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*/
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#ifdef USE_ASSERT_CHECKING
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static inline Node*
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castNodeImpl(enum NodeTag type, void *ptr)
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{
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Assert(ptr == NULL || nodeTag(ptr) == type);
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return ptr;
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}
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#define castNode(_type_, nodeptr) ((_type_ *) castNodeImpl(T_##_type_, nodeptr))
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#else
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#define castNode(_type_,nodeptr) ((_type_ *)(nodeptr))
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#endif
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/* ----------------------------------------------------------------
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* extern declarations follow
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* ----------------------------------------------------------------

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