| Message ID | 20240301150812.95213-1-jwakely@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | libstdc++: Better diagnostics for std::format errors | expand |
Pushed to trunk. On Fri, 1 Mar 2024 at 15:09, Jonathan Wakely <jwakely@redhat.com> wrote: > Does the text of these new diagnostics look good? > > There are of course other ways for a type to be not-formattable (e.g. > the formatter::format member doesn't return the right type or has some > other kind of incorrect signature, or the formatter::parse member isn't > constexpr) but we can't predict/detect them all reliably. This just > attempts to give a user-friendly explanation for a couple of common > mistakes. It should not have any false positives, because the > basic_format_arg constructor requires __formattable_with<_Tp, _Context> > so if either of these assertions fails, constructing __arg will fail > too. The static_assert only adds a more readable error for a > compilation that's going to fail anyway. > > Tested x86_64-linux. > > -- >8 -- > > This adds two new static_assert messages to the internals of > std::make_format_args to give better diagnostics for invalid format > args. Rather than just getting an error saying that basic_format_arg > cannot be constructed, we get more specific errors for the cases where > std::formatter isn't specialized for the type at all, and where it's > specialized but only meets the BasicFormatter requirements and so can > only format non-const arguments. > > Also add a test for the existing static_assert when constructing a > format_string for non-formattable args. > > libstdc++-v3/ChangeLog: > > * include/std/format (_Arg_store::_S_make_elt): Add two > static_assert checks to give more user-friendly error messages. > * testsuite/lib/prune.exp (libstdc++-dg-prune): Prune another > form of "in requirements with" note. > * testsuite/std/format/arguments/args_neg.cc: Check for > user-friendly diagnostics for non-formattable types. > * testsuite/std/format/string_neg.cc: Likewise. > --- > libstdc++-v3/include/std/format | 13 +++++++ > libstdc++-v3/testsuite/lib/prune.exp | 1 + > .../std/format/arguments/args_neg.cc | 34 ++++++++++++++++++- > .../testsuite/std/format/string_neg.cc | 4 +++ > 4 files changed, 51 insertions(+), 1 deletion(-) > > diff --git a/libstdc++-v3/include/std/format > b/libstdc++-v3/include/std/format > index ee189f9086c..1e839e88db4 100644 > --- a/libstdc++-v3/include/std/format > +++ b/libstdc++-v3/include/std/format > @@ -3704,6 +3704,19 @@ namespace __format > static _Element_t > _S_make_elt(_Tp& __v) > { > + using _Tq = remove_const_t<_Tp>; > + using _CharT = typename _Context::char_type; > + static_assert(is_default_constructible_v<formatter<_Tq, _CharT>>, > + "std::formatter must be specialized for the type " > + "of each format arg"); > + using __format::__formattable_with; > + if constexpr (is_const_v<_Tp>) > + if constexpr (!__formattable_with<_Tp, _Context>) > + if constexpr (__formattable_with<_Tq, _Context>) > + static_assert(__formattable_with<_Tp, _Context>, > + "format arg must be non-const because its " > + "std::formatter specialization has a " > + "non-const reference parameter"); > basic_format_arg<_Context> __arg(__v); > if constexpr (_S_values_only) > return __arg._M_val; > diff --git a/libstdc++-v3/testsuite/lib/prune.exp > b/libstdc++-v3/testsuite/lib/prune.exp > index 24a15ccad22..071dcf34c1e 100644 > --- a/libstdc++-v3/testsuite/lib/prune.exp > +++ b/libstdc++-v3/testsuite/lib/prune.exp > @@ -54,6 +54,7 @@ proc libstdc++-dg-prune { system text } { > regsub -all "(^|\n)\[^\n\]*: . skipping \[0-9\]* instantiation > contexts \[^\n\]*" $text "" text > regsub -all "(^|\n)\[^\n\]*: in .constexpr. expansion \[^\n\]*" > $text "" text > regsub -all "(^|\n)\[^\n\]*: in requirements .with\[^\n\]*" $text > "" text > + regsub -all "(^|\n)\[^\n\]*: in requirements with\[^\n\]*" $text "" > text > regsub -all "(^|\n) inlined from \[^\n\]*" $text "" text > # Why doesn't GCC need these to strip header context? > regsub -all "(^|\n)In file included from \[^\n\]*" $text "" text > diff --git a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc > b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc > index 16ac3040146..ded56fe63ab 100644 > --- a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc > +++ b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc > @@ -6,7 +6,39 @@ > > std::string rval() { return "path/etic/experience"; } > > -void f() > +void test_rval() > { > (void)std::make_format_args(rval()); // { dg-error "cannot bind > non-const lvalue reference" } > } > + > +void test_missing_specialization() > +{ > + struct X { }; > + X x; > + (void)std::make_format_args(x); // { dg-error "here" } > +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 } > +} > + > +struct Y { }; > +template<> class std::formatter<Y> { > +public: > + constexpr typename format_parse_context::iterator > + parse(format_parse_context& c) > + { return c.begin(); } > + > + template<class C> > + typename C::iterator format(Y&, C&) const; > +}; > + > +void test(std::formatter<Y>& f, std::format_parse_context& pc) { > + f.parse(pc); > +} > + > +void test_const_arg() > +{ > + const Y y; > + (void)std::make_format_args(y); // { dg-error "here" } > +// { dg-error "format arg must be non-const" "" { target *-*-* } 0 } > +} > + > +// { dg-prune-output "no matching function for call to > .*::basic_format_arg<" } > diff --git a/libstdc++-v3/testsuite/std/format/string_neg.cc > b/libstdc++-v3/testsuite/std/format/string_neg.cc > index 69bcc736cff..d5963145b18 100644 > --- a/libstdc++-v3/testsuite/std/format/string_neg.cc > +++ b/libstdc++-v3/testsuite/std/format/string_neg.cc > @@ -4,3 +4,7 @@ > > auto s = std::format(" {9} "); // { dg-error "call to consteval function" > } > // { dg-error "invalid.arg.id" "" { target *-*-* } 0 } > + > +struct X { }; > +std::format_string<X> str(""); // dg-error "here" } > +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 } > -- > 2.43.2 > >
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format index ee189f9086c..1e839e88db4 100644 --- a/libstdc++-v3/include/std/format +++ b/libstdc++-v3/include/std/format @@ -3704,6 +3704,19 @@ namespace __format static _Element_t _S_make_elt(_Tp& __v) { + using _Tq = remove_const_t<_Tp>; + using _CharT = typename _Context::char_type; + static_assert(is_default_constructible_v<formatter<_Tq, _CharT>>, + "std::formatter must be specialized for the type " + "of each format arg"); + using __format::__formattable_with; + if constexpr (is_const_v<_Tp>) + if constexpr (!__formattable_with<_Tp, _Context>) + if constexpr (__formattable_with<_Tq, _Context>) + static_assert(__formattable_with<_Tp, _Context>, + "format arg must be non-const because its " + "std::formatter specialization has a " + "non-const reference parameter"); basic_format_arg<_Context> __arg(__v); if constexpr (_S_values_only) return __arg._M_val; diff --git a/libstdc++-v3/testsuite/lib/prune.exp b/libstdc++-v3/testsuite/lib/prune.exp index 24a15ccad22..071dcf34c1e 100644 --- a/libstdc++-v3/testsuite/lib/prune.exp +++ b/libstdc++-v3/testsuite/lib/prune.exp @@ -54,6 +54,7 @@ proc libstdc++-dg-prune { system text } { regsub -all "(^|\n)\[^\n\]*: . skipping \[0-9\]* instantiation contexts \[^\n\]*" $text "" text regsub -all "(^|\n)\[^\n\]*: in .constexpr. expansion \[^\n\]*" $text "" text regsub -all "(^|\n)\[^\n\]*: in requirements .with\[^\n\]*" $text "" text + regsub -all "(^|\n)\[^\n\]*: in requirements with\[^\n\]*" $text "" text regsub -all "(^|\n) inlined from \[^\n\]*" $text "" text # Why doesn't GCC need these to strip header context? regsub -all "(^|\n)In file included from \[^\n\]*" $text "" text diff --git a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc index 16ac3040146..ded56fe63ab 100644 --- a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc +++ b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc @@ -6,7 +6,39 @@ std::string rval() { return "path/etic/experience"; } -void f() +void test_rval() { (void)std::make_format_args(rval()); // { dg-error "cannot bind non-const lvalue reference" } } + +void test_missing_specialization() +{ + struct X { }; + X x; + (void)std::make_format_args(x); // { dg-error "here" } +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 } +} + +struct Y { }; +template<> class std::formatter<Y> { +public: + constexpr typename format_parse_context::iterator + parse(format_parse_context& c) + { return c.begin(); } + + template<class C> + typename C::iterator format(Y&, C&) const; +}; + +void test(std::formatter<Y>& f, std::format_parse_context& pc) { + f.parse(pc); +} + +void test_const_arg() +{ + const Y y; + (void)std::make_format_args(y); // { dg-error "here" } +// { dg-error "format arg must be non-const" "" { target *-*-* } 0 } +} + +// { dg-prune-output "no matching function for call to .*::basic_format_arg<" } diff --git a/libstdc++-v3/testsuite/std/format/string_neg.cc b/libstdc++-v3/testsuite/std/format/string_neg.cc index 69bcc736cff..d5963145b18 100644 --- a/libstdc++-v3/testsuite/std/format/string_neg.cc +++ b/libstdc++-v3/testsuite/std/format/string_neg.cc @@ -4,3 +4,7 @@ auto s = std::format(" {9} "); // { dg-error "call to consteval function" } // { dg-error "invalid.arg.id" "" { target *-*-* } 0 } + +struct X { }; +std::format_string<X> str(""); // dg-error "here" } +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 }