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Fix dead ill-formed-fourth-byte UTF-8 test sections (byte3/byte4 typo) (#5499)

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* Fix dead ill-formed-fourth-byte UTF-8 test sections (byte3/byte4 typo)

The "ill-formed: wrong fourth byte" SECTIONs in unit-unicode3.cpp,
unit-unicode4.cpp, and unit-unicode5.cpp guarded their loop with a check
on byte3 instead of byte4. Since the enclosing loop already restricts
byte3 to its valid range, the guard was always true and the section's
"continue" fired unconditionally, so check_utf8string()/check_utf8dump()
were never actually invoked for a malformed fourth byte.

Fixing the guard naively (byte3 -> byte4) would also have swept the full
byte2 x byte3 combinatorics for every byte4 value, adding millions of
redundant iterations: the lexer validates continuation bytes strictly in
sequence with early exit (see next_byte_in_range() in lexer.hpp), so once
byte2/byte3 are within their valid range, the byte4 outcome does not
depend on which valid byte2/byte3 values were chosen. Instead, byte2 and
byte3 are now held to a small hedge of representative valid prefixes
(range corners plus a midpoint) while byte4 is still swept exhaustively
over its full 0x00-0xFF range, since that is the actual property under
test. Also fixed the garbled "skip fourth second byte" comment in
unit-unicode3.cpp.

Verified offline: before the fix, the "wrong fourth byte" subcase
executes 0 assertions in all three files (proving it was dead code);
after the fix, it executes 11520 (unicode3), 34560 (unicode4), and 11520
(unicode5) assertions, and a deliberately reintroduced bug in the
lexer's byte4 range check causes it to fail (proving it is now
meaningful). Total per-file assertion counts grow by the same small
amounts, not by millions, and all other sections in these files still
pass unchanged.

Fixes #5416

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Keep full byte2 x byte3 combinatorics in the wrong-fourth-byte sections

The maintainer wants exhaustive coverage of every byte combination here
rather than the representative-prefix reduction, matching the style of
the sibling "wrong second/third byte" sections in the same files.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-16 20:16:43 +02:00
committed by GitHub
parent 29ba5973b6
commit e8e1ba0db9
3 changed files with 4 additions and 4 deletions
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4
tests/src/unit-unicode3.cpp
View File

@@ -306,8 +306,8 @@ TEST_CASE("Unicode (3/5)" * doctest::skip())
{
for (int byte4 = 0x00; byte4 <= 0xFF; ++byte4)
{
// skip fourth second byte
if (0x80 <= byte3 && byte3 <= 0xBF)
// skip correct fourth byte
if (0x80 <= byte4 && byte4 <= 0xBF)
{
continue;
}

2
tests/src/unit-unicode4.cpp
View File

@@ -307,7 +307,7 @@ TEST_CASE("Unicode (4/5)" * doctest::skip())
for (int byte4 = 0x00; byte4 <= 0xFF; ++byte4)
{
// skip correct fourth byte
if (0x80 <= byte3 && byte3 <= 0xBF)
if (0x80 <= byte4 && byte4 <= 0xBF)
{
continue;
}

2
tests/src/unit-unicode5.cpp
View File

@@ -307,7 +307,7 @@ TEST_CASE("Unicode (5/5)" * doctest::skip())
for (int byte4 = 0x00; byte4 <= 0xFF; ++byte4)
{
// skip correct fourth byte
if (0x80 <= byte3 && byte3 <= 0xBF)
if (0x80 <= byte4 && byte4 <= 0xBF)
{
continue;
}