conditional.h

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/*-------------------------------------------------------------------------
 * A stack of automaton states to handle nested conditionals.
 *
 * This file describes a stack of automaton states which
 * allow a manage nested conditionals.
 *
 * It is used by:
 * - "psql" interpreter for handling \if ... \endif
 * - "pgbench" interpreter for handling \if ... \endif
 * - "pgbench" syntax checker to test for proper nesting
 *
 * The stack holds the state of enclosing conditionals (are we in
 * a true branch? in a false branch? have we already encountered
 * a true branch?) so that the interpreter knows whether to execute
 * code and whether to evaluate conditions.
 *
 * Copyright (c) 2000-2024, PostgreSQL Global Development Group
 *
 * src/include/fe_utils/conditional.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef CONDITIONAL_H
#define CONDITIONAL_H
 
/*
 * Possible states of a single level of \if block.
 */
typedef enum ifState
{
    IFSTATE_NONE = 0,           /* not currently in an \if block */
    IFSTATE_TRUE,               /* currently in an \if or \elif that is true
                                 * and all parent branches (if any) are true */
    IFSTATE_FALSE,              /* currently in an \if or \elif that is false
                                 * but no true branch has yet been seen, and
                                 * all parent branches (if any) are true */
    IFSTATE_IGNORED,            /* currently in an \elif that follows a true
                                 * branch, or the whole \if is a child of a
                                 * false parent branch */
    IFSTATE_ELSE_TRUE,          /* currently in an \else that is true and all
                                 * parent branches (if any) are true */
    IFSTATE_ELSE_FALSE,         /* currently in an \else that is false or
                                 * ignored */
} ifState;
 
/*
 * The state of nested \ifs is stored in a stack.
 *
 * query_len is used to determine what accumulated text to throw away at the
 * end of an inactive branch.  (We could, perhaps, teach the lexer to not add
 * stuff to the query buffer in the first place when inside an inactive branch;
 * but that would be very invasive.)  We also need to save and restore the
 * lexer's parenthesis nesting depth when throwing away text.  (We don't need
 * to save and restore any of its other state, such as comment nesting depth,
 * because a backslash command could never appear inside a comment or SQL
 * literal.)
 */
typedef struct IfStackElem
{
    ifState     if_state;       /* current state, see enum above */
    int         query_len;      /* length of query_buf at last branch start */
    int         paren_depth;    /* parenthesis depth at last branch start */
    struct IfStackElem *next;   /* next surrounding \if, if any */
} IfStackElem;
 
typedef struct ConditionalStackData
{
    IfStackElem *head;
}           ConditionalStackData;
 
typedef struct ConditionalStackData *ConditionalStack;
 
 
extern ConditionalStack conditional_stack_create(void);
 
extern void conditional_stack_reset(ConditionalStack cstack);
 
extern void conditional_stack_destroy(ConditionalStack cstack);
 
extern int  conditional_stack_depth(ConditionalStack cstack);
 
extern void conditional_stack_push(ConditionalStack cstack, ifState new_state);
 
extern bool conditional_stack_pop(ConditionalStack cstack);
 
extern ifState conditional_stack_peek(ConditionalStack cstack);
 
extern bool conditional_stack_poke(ConditionalStack cstack, ifState new_state);
 
extern bool conditional_stack_empty(ConditionalStack cstack);
 
extern bool conditional_active(ConditionalStack cstack);
 
extern void conditional_stack_set_query_len(ConditionalStack cstack, int len);
 
extern int  conditional_stack_get_query_len(ConditionalStack cstack);
 
extern void conditional_stack_set_paren_depth(ConditionalStack cstack, int depth);
 
extern int  conditional_stack_get_paren_depth(ConditionalStack cstack);
 
#endif                          /* CONDITIONAL_H */