gdbsupport/valid-expr.h

   1 /* Compile-time valid expression checker for GDB, the GNU debugger.
   2
   3    Copyright (C) 2017-2021 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 /* Helper macros used to build compile-time unit tests that make sure
  21    that invalid expressions that should not compile would not compile,
  22    and that expressions that should compile do compile, and have the
  23    right type.  This is mainly used to verify that some utility's API
  24    is really as safe as intended.  */
  25
  26 #ifndef COMMON_VALID_EXPR_H
  27 #define COMMON_VALID_EXPR_H
  28
  29 #include "gdbsupport/preprocessor.h"
  30 #include "gdbsupport/traits.h"
  31
  32 /* Macro that uses SFINAE magic to detect whether the EXPR expression
  33    is either valid or ill-formed, at compile time, without actually
  34    producing compile-time errors.  I.e., check that bad uses of the
  35    types (e.g., involving mismatching types) would be caught at
  36    compile time.  If the expression is valid, also check whether the
  37    expression has the right type.
  38
  39    EXPR must be defined in terms of some of the template parameters,
  40    so that template substitution failure discards the overload instead
  41    of causing a real compile error.  TYPES is thus the list of types
  42    involved in the expression, and TYPENAMES is the same list, but
  43    with each element prefixed by "typename".  These are passed as
  44    template parameter types to the templates within the macro.
  45
  46    VALID is a boolean that indicates whether the expression is
  47    supposed to be valid or invalid.
  48
  49    EXPR_TYPE is the expected type of EXPR.  Only meaningful iff VALID
  50    is true.  If VALID is false, then you must pass "void" as expected
  51    type.
  52
  53    Each invocation of the macro is wrapped in its own namespace to
  54    avoid ODR violations.  The generated namespace only includes the
  55    line number, so client code should wrap sets of calls in a
  56    test-specific namespace too, to fully guarantee uniqueness between
  57    the multiple clients in the codebase.  */
  58 #define CHECK_VALID_EXPR_INT(TYPENAMES, TYPES, VALID, EXPR_TYPE, EXPR)  \
  59   namespace CONCAT (check_valid_expr, __LINE__) {                       \
  60                                                                         \
  61   template <TYPENAMES, typename = decltype (EXPR)>                      \
  62   struct archetype                                                      \
  63   {                                                                     \
  64   };                                                                    \
  65                                                                         \
  66   static_assert (gdb::is_detected_exact<archetype<TYPES, EXPR_TYPE>,    \
  67                  archetype, TYPES>::value == VALID,                     \
  68                  "");                                                   \
  69   } /* namespace */
  70
  71 /* A few convenience macros that support expressions involving a
  72    varying numbers of types.  If you need more types, feel free to add
  73    another variant.  */
  74
  75 #define CHECK_VALID_EXPR_1(T1, VALID, EXPR_TYPE, EXPR)                  \
  76   CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1),                       \
  77                         ESC_PARENS (T1),                                \
  78                         VALID, EXPR_TYPE, EXPR)
  79
  80 #define CHECK_VALID_EXPR_2(T1, T2, VALID, EXPR_TYPE, EXPR)              \
  81   CHECK_VALID_EXPR_INT (ESC_PARENS(typename T1, typename T2),           \
  82                         ESC_PARENS (T1, T2),                            \
  83                         VALID, EXPR_TYPE, EXPR)
  84
  85 #define CHECK_VALID_EXPR_3(T1, T2, T3, VALID, EXPR_TYPE, EXPR)          \
  86   CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2, typename T3), \
  87                         ESC_PARENS (T1, T2, T3),                                \
  88                         VALID, EXPR_TYPE, EXPR)
  89
  90 #define CHECK_VALID_EXPR_4(T1, T2, T3, T4, VALID, EXPR_TYPE, EXPR)      \
  91   CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2,           \
  92                                     typename T3, typename T4),          \
  93                         ESC_PARENS (T1, T2, T3, T4),                    \
  94                         VALID, EXPR_TYPE, EXPR)
  95
  96 #define CHECK_VALID_EXPR_5(T1, T2, T3, T4, T5, VALID, EXPR_TYPE, EXPR)  \
  97   CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2,           \
  98                                     typename T3, typename T4,           \
  99                                     typename T5),                       \
 100                         ESC_PARENS (T1, T2, T3, T4, T5),                \
 101                         VALID, EXPR_TYPE, EXPR)
 102
 103 #define CHECK_VALID_EXPR_6(T1, T2, T3, T4, T5, T6,                      \
 104                            VALID, EXPR_TYPE, EXPR)                      \
 105   CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2,           \
 106                                     typename T3, typename T4,           \
 107                                     typename T5, typename T6),          \
 108                         ESC_PARENS (T1, T2, T3, T4, T5, T6),            \
 109                         VALID, EXPR_TYPE, EXPR)
 110
 111 #endif /* COMMON_VALID_EXPR_H */