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1945192cb9
An earlier attempt at doing this had failed (wouldn't work in GCCs around 4.8, IIRC), but now that I try again, it works. I suspect that my previous attempt did not use the pre C++14-safe void_t (in traits.h). I want to switch to this model because: - It's the standard detection idiom that folks will learn starting with C++17. - In the enum_flags unit tests, I have a static_assert that triggers a warning (resulting in build error), which GCC does not suppress because the warning is not being triggered in the SFINAE context. Switching to the detection idiom fixes that. Alternatively, switching to the C++03-style expression-validity checking with a varargs overload would allow addressing that, but I think that would be going backwards idiomatically speaking. - While this patch shows a net increase of lines of code, the magic being added to traits.h can be removed in a few years when we start requiring C++17. gdbsupport/ChangeLog: * traits.h (struct nonesuch, struct detector, detected_or) (detected_or_t, is_detected, detected_t, detected_or) (detected_or_t, is_detected_exact, is_detected_convertible): New. * valid-expr.h (CHECK_VALID_EXPR_INT): Use gdb::is_detected_exact.
95 lines
3.8 KiB
C++
95 lines
3.8 KiB
C++
/* Compile-time valid expression checker for GDB, the GNU debugger.
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Copyright (C) 2017-2020 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* Helper macros used to build compile-time unit tests that make sure
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that invalid expressions that should not compile would not compile,
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and that expressions that should compile do compile, and have the
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right type. This is mainly used to verify that some utility's API
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is really as safe as intended. */
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#ifndef COMMON_VALID_EXPR_H
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#define COMMON_VALID_EXPR_H
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#include "gdbsupport/preprocessor.h"
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#include "gdbsupport/traits.h"
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/* Macro that uses SFINAE magic to detect whether the EXPR expression
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is either valid or ill-formed, at compile time, without actually
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producing compile-time errors. I.e., check that bad uses of the
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types (e.g., involving mismatching types) would be caught at
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compile time. If the expression is valid, also check whether the
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expression has the right type.
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EXPR must be defined in terms of some of the template parameters,
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so that template substitution failure discards the overload instead
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of causing a real compile error. TYPES is thus the list of types
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involved in the expression, and TYPENAMES is the same list, but
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with each element prefixed by "typename". These are passed as
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template parameter types to the templates within the macro.
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VALID is a boolean that indicates whether the expression is
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supposed to be valid or invalid.
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EXPR_TYPE is the expected type of EXPR. Only meaningful iff VALID
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is true. If VALID is false, then you must pass "void" as expected
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type.
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Each invocation of the macro is wrapped in its own namespace to
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avoid ODR violations. The generated namespace only includes the
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line number, so client code should wrap sets of calls in a
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test-specific namespace too, to fully guarantee uniqueness between
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the multiple clients in the codebase. */
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#define CHECK_VALID_EXPR_INT(TYPENAMES, TYPES, VALID, EXPR_TYPE, EXPR) \
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namespace CONCAT (check_valid_expr, __LINE__) { \
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\
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template <TYPENAMES> \
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using archetype = decltype (EXPR); \
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\
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static_assert (gdb::is_detected_exact<EXPR_TYPE, \
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archetype, TYPES>::value == VALID, \
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""); \
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} /* namespace */
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/* A few convenience macros that support expressions involving a
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varying numbers of types. If you need more types, feel free to add
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another variant. */
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#define CHECK_VALID_EXPR_1(T1, VALID, EXPR_TYPE, EXPR) \
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CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1), \
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ESC_PARENS (T1), \
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VALID, EXPR_TYPE, EXPR)
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#define CHECK_VALID_EXPR_2(T1, T2, VALID, EXPR_TYPE, EXPR) \
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CHECK_VALID_EXPR_INT (ESC_PARENS(typename T1, typename T2), \
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ESC_PARENS (T1, T2), \
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VALID, EXPR_TYPE, EXPR)
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#define CHECK_VALID_EXPR_3(T1, T2, T3, VALID, EXPR_TYPE, EXPR) \
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CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2, typename T3), \
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ESC_PARENS (T1, T2, T3), \
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VALID, EXPR_TYPE, EXPR)
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#define CHECK_VALID_EXPR_4(T1, T2, T3, T4, VALID, EXPR_TYPE, EXPR) \
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CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2, \
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typename T3, typename T4), \
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ESC_PARENS (T1, T2, T3, T4), \
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VALID, EXPR_TYPE, EXPR)
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#endif /* COMMON_VALID_EXPR_H */
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