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Fix missing named-arg validation for compiled format strings #4638

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Merged
vitaut merged 6 commits into from
Jan 4, 2026
Merged

Fix missing named-arg validation for compiled format strings #4638

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41634ec
Create compilation error tests for FMT_COMPILE missing named argument…
jaeheonshim Dec 29, 2025
f3ad65c
During format string compilation, static assert that either the forma…
jaeheonshim Dec 29, 2025
3c44f2d
Remove duplicate named argument test for now
jaeheonshim Dec 30, 2025
bc1cb1a
Fix formatting
jaeheonshim Dec 30, 2025
d22d2d5
Add missing newline
jaeheonshim Jan 3, 2026
8dd4b48
Remove compilation error tests
jaeheonshim Jan 3, 2026
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55 changes: 34 additions & 21 deletions include/fmt/compile.h
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Original file line number Diff line number Diff line change
Expand Up @@ -267,13 +267,15 @@ constexpr auto parse_text(basic_string_view<Char> str, size_t pos) -> size_t {
return pos;
}

template <typename Args, size_t POS, int ID, typename S>
template <typename Args, size_t POS, int ID, bool DYNAMIC_NAMES, typename S>
constexpr auto compile_format_string(S fmt);

template <typename Args, size_t POS, int ID, typename T, typename S>
template <typename Args, size_t POS, int ID, bool DYNAMIC_NAMES, typename T,
typename S>
constexpr auto parse_tail(T head, S fmt) {
if constexpr (POS != basic_string_view<typename S::char_type>(fmt).size()) {
constexpr auto tail = compile_format_string<Args, POS, ID>(fmt);
constexpr auto tail =
compile_format_string<Args, POS, ID, DYNAMIC_NAMES>(fmt);
if constexpr (std::is_same<remove_cvref_t<decltype(tail)>,
unknown_format>())
return tail;
Expand Down Expand Up @@ -347,13 +349,13 @@ struct field_type<T, enable_if_t<detail::is_named_arg<T>::value>> {
};

template <typename T, typename Args, size_t END_POS, int ARG_INDEX, int NEXT_ID,
typename S>
bool DYNAMIC_NAMES, typename S>
constexpr auto parse_replacement_field_then_tail(S fmt) {
using char_type = typename S::char_type;
constexpr auto str = basic_string_view<char_type>(fmt);
constexpr char_type c = END_POS != str.size() ? str[END_POS] : char_type();
if constexpr (c == '}') {
return parse_tail<Args, END_POS + 1, NEXT_ID>(
return parse_tail<Args, END_POS + 1, NEXT_ID, DYNAMIC_NAMES>(
field<char_type, typename field_type<T>::type, ARG_INDEX>(), fmt);
} else if constexpr (c != ':') {
FMT_THROW(format_error("expected ':'"));
Expand All @@ -364,7 +366,8 @@ constexpr auto parse_replacement_field_then_tail(S fmt) {
FMT_THROW(format_error("expected '}'"));
return 0;
} else {
return parse_tail<Args, result.end + 1, result.next_arg_id>(
return parse_tail<Args, result.end + 1, result.next_arg_id,
DYNAMIC_NAMES>(
spec_field<char_type, typename field_type<T>::type, ARG_INDEX>{
result.fmt},
fmt);
Expand All @@ -374,22 +377,23 @@ constexpr auto parse_replacement_field_then_tail(S fmt) {

// Compiles a non-empty format string and returns the compiled representation
// or unknown_format() on unrecognized input.
template <typename Args, size_t POS, int ID, typename S>
template <typename Args, size_t POS, int ID, bool DYNAMIC_NAMES, typename S>
constexpr auto compile_format_string(S fmt) {
using char_type = typename S::char_type;
constexpr auto str = basic_string_view<char_type>(fmt);
if constexpr (str[POS] == '{') {
if constexpr (POS + 1 == str.size())
FMT_THROW(format_error("unmatched '{' in format string"));
if constexpr (str[POS + 1] == '{') {
return parse_tail<Args, POS + 2, ID>(make_text(str, POS, 1), fmt);
return parse_tail<Args, POS + 2, ID, DYNAMIC_NAMES>(
make_text(str, POS, 1), fmt);
} else if constexpr (str[POS + 1] == '}' || str[POS + 1] == ':') {
static_assert(ID != manual_indexing_id,
"cannot switch from manual to automatic argument indexing");
constexpr auto next_id =
ID != manual_indexing_id ? ID + 1 : manual_indexing_id;
return parse_replacement_field_then_tail<get_type<ID, Args>, Args,
POS + 1, ID, next_id>(fmt);
return parse_replacement_field_then_tail<
get_type<ID, Args>, Args, POS + 1, ID, next_id, DYNAMIC_NAMES>(fmt);
} else {
constexpr auto arg_id_result =
parse_arg_id<ID>(str.data() + POS + 1, str.data() + str.size());
Expand All @@ -402,21 +406,24 @@ constexpr auto compile_format_string(S fmt) {
ID == manual_indexing_id || ID == 0,
"cannot switch from automatic to manual argument indexing");
constexpr auto arg_index = arg_id_result.arg_id.index;
return parse_replacement_field_then_tail<get_type<arg_index, Args>,
Args, arg_id_end_pos,
arg_index, manual_indexing_id>(
fmt);
return parse_replacement_field_then_tail<
get_type<arg_index, Args>, Args, arg_id_end_pos, arg_index,
manual_indexing_id, DYNAMIC_NAMES>(fmt);
} else if constexpr (arg_id_result.kind == arg_id_kind::name) {
constexpr auto arg_index =
get_arg_index_by_name(arg_id_result.arg_id.name, Args{});

static_assert(arg_index >= 0 || DYNAMIC_NAMES,
"named argument not found");

if constexpr (arg_index >= 0) {
constexpr auto next_id =
ID != manual_indexing_id ? ID + 1 : manual_indexing_id;
return parse_replacement_field_then_tail<
decltype(get_type<arg_index, Args>::value), Args, arg_id_end_pos,
arg_index, next_id>(fmt);
arg_index, next_id, DYNAMIC_NAMES>(fmt);
} else if constexpr (c == '}') {
return parse_tail<Args, arg_id_end_pos + 1, ID>(
return parse_tail<Args, arg_id_end_pos + 1, ID, DYNAMIC_NAMES>(
runtime_named_field<char_type>{arg_id_result.arg_id.name}, fmt);
} else if constexpr (c == ':') {
return unknown_format(); // no type info for specs parsing
Expand All @@ -426,13 +433,16 @@ constexpr auto compile_format_string(S fmt) {
} else if constexpr (str[POS] == '}') {
if constexpr (POS + 1 == str.size())
FMT_THROW(format_error("unmatched '}' in format string"));
return parse_tail<Args, POS + 2, ID>(make_text(str, POS, 1), fmt);
return parse_tail<Args, POS + 2, ID, DYNAMIC_NAMES>(make_text(str, POS, 1),
fmt);
} else {
constexpr auto end = parse_text(str, POS + 1);
if constexpr (end - POS > 1) {
return parse_tail<Args, end, ID>(make_text(str, POS, end - POS), fmt);
return parse_tail<Args, end, ID, DYNAMIC_NAMES>(
make_text(str, POS, end - POS), fmt);
} else {
return parse_tail<Args, end, ID>(code_unit<char_type>{str[POS]}, fmt);
return parse_tail<Args, end, ID, DYNAMIC_NAMES>(
code_unit<char_type>{str[POS]}, fmt);
}
}
}
Expand All @@ -444,8 +454,11 @@ constexpr auto compile(S fmt) {
if constexpr (str.size() == 0) {
return detail::make_text(str, 0, 0);
} else {
constexpr auto result =
detail::compile_format_string<detail::type_list<Args...>, 0, 0>(fmt);
constexpr int num_static_named_args =
detail::count_static_named_args<Args...>();
constexpr auto result = detail::compile_format_string<
detail::type_list<Args...>, 0, 0,
num_static_named_args != detail::count_named_args<Args...>()>(fmt);
return result;
}
}
Expand Down
1 change: 1 addition & 0 deletions test/compile-error-test/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ set(fmt_headers "
#include <fmt/format.h>
#include <fmt/xchar.h>
#include <fmt/ostream.h>
#include <fmt/compile.h>
#include <iostream>
")

Expand Down