src/include/fe_utils/conditional.h

   1 /*-------------------------------------------------------------------------
   2  * A stack of automaton states to handle nested conditionals.
   3  *
   4  * This file describes a stack of automaton states which
   5  * allow a manage nested conditionals.
   6  *
   7  * It is used by:
   8  * - "psql" interpreter for handling \if ... \endif
   9  * - "pgbench" interpreter for handling \if ... \endif
  10  * - "pgbench" syntax checker to test for proper nesting
  11  *
  12  * The stack holds the state of enclosing conditionals (are we in
  13  * a true branch? in a false branch? have we already encountered
  14  * a true branch?) so that the interpreter knows whether to execute
  15  * code and whether to evaluate conditions.
  16  *
  17  * Copyright (c) 2000-2021, PostgreSQL Global Development Group
  18  *
  19  * src/include/fe_utils/conditional.h
  20  *
  21  *-------------------------------------------------------------------------
  22  */
  23 #ifndef CONDITIONAL_H
  24 #define CONDITIONAL_H
  25
  26 /*
  27  * Possible states of a single level of \if block.
  28  */
  29 typedef enum ifState
  30 {
  31         IFSTATE_NONE = 0,                       /* not currently in an \if block */
  32         IFSTATE_TRUE,                           /* currently in an \if or \elif that is true
  33                                                                  * and all parent branches (if any) are true */
  34         IFSTATE_FALSE,                          /* currently in an \if or \elif that is false
  35                                                                  * but no true branch has yet been seen, and
  36                                                                  * all parent branches (if any) are true */
  37         IFSTATE_IGNORED,                        /* currently in an \elif that follows a true
  38                                                                  * branch, or the whole \if is a child of a
  39                                                                  * false parent branch */
  40         IFSTATE_ELSE_TRUE,                      /* currently in an \else that is true and all
  41                                                                  * parent branches (if any) are true */
  42         IFSTATE_ELSE_FALSE                      /* currently in an \else that is false or
  43                                                                  * ignored */
  44 } ifState;
  45
  46 /*
  47  * The state of nested \ifs is stored in a stack.
  48  *
  49  * query_len is used to determine what accumulated text to throw away at the
  50  * end of an inactive branch.  (We could, perhaps, teach the lexer to not add
  51  * stuff to the query buffer in the first place when inside an inactive branch;
  52  * but that would be very invasive.)  We also need to save and restore the
  53  * lexer's parenthesis nesting depth when throwing away text.  (We don't need
  54  * to save and restore any of its other state, such as comment nesting depth,
  55  * because a backslash command could never appear inside a comment or SQL
  56  * literal.)
  57  */
  58 typedef struct IfStackElem
  59 {
  60         ifState         if_state;               /* current state, see enum above */
  61         int                     query_len;              /* length of query_buf at last branch start */
  62         int                     paren_depth;    /* parenthesis depth at last branch start */
  63         struct IfStackElem *next;       /* next surrounding \if, if any */
  64 } IfStackElem;
  65
  66 typedef struct ConditionalStackData
  67 {
  68         IfStackElem *head;
  69 }                       ConditionalStackData;
  70
  71 typedef struct ConditionalStackData *ConditionalStack;
  72
  73
  74 extern ConditionalStack conditional_stack_create(void);
  75
  76 extern void conditional_stack_destroy(ConditionalStack cstack);
  77
  78 extern int      conditional_stack_depth(ConditionalStack cstack);
  79
  80 extern void conditional_stack_push(ConditionalStack cstack, ifState new_state);
  81
  82 extern bool conditional_stack_pop(ConditionalStack cstack);
  83
  84 extern ifState conditional_stack_peek(ConditionalStack cstack);
  85
  86 extern bool conditional_stack_poke(ConditionalStack cstack, ifState new_state);
  87
  88 extern bool conditional_stack_empty(ConditionalStack cstack);
  89
  90 extern bool conditional_active(ConditionalStack cstack);
  91
  92 extern void conditional_stack_set_query_len(ConditionalStack cstack, int len);
  93
  94 extern int      conditional_stack_get_query_len(ConditionalStack cstack);
  95
  96 extern void conditional_stack_set_paren_depth(ConditionalStack cstack, int depth);
  97
  98 extern int      conditional_stack_get_paren_depth(ConditionalStack cstack);
  99
 100 #endif                                                  /* CONDITIONAL_H */