[Tarantool-patches] [PATCH luajit v3 16/29] test: adapt PUC-Rio test for %q in string.format

[Sergey Kaplun]

LuaJIT since v2.0.0-beta6 has extension from Lua 5.2:
string.format(): %q reversible.
See also https://luajit.org/extensions.html#lua52.

The q option formats a string in a form suitable to be safely read
back by the Lua interpreter [1].

In Lua 5.1, '\0' was converted to "\000" unconditionally.

In Lua 5.2, control characters are written as \nnn when needed, see
d62a21b9d379a576bae7426c80039ca1a4d2bb07 ("when formatting with '%q',
all control characters are coded as \nnn.") [1]. In this patch, %q
specifier starts writing control characters to a new string in the same
way through \d, instead of their binary representation as it is. If the
control character is followed by a digit, then for the correct work of
the parser, it is necessary to extend the escape sequence to 3
significant characters (otherwise, the transition "\0002" -> "\02"
corrupts string). For this patch, the expansion is performed
unconditionally (the check for the next symbol is not performed) if this
first symbol is a zero byte.

Consistent work with the zero byte processing omitting the custom check
was added in the commit 658ea8752b979102627e2fede7b7ddfbb67ba6c9 ("no
need to handle '\0' differently from other control chars in format
'%q'") [2]. Note, that this patch does not change the semantics of %q
specifier - the new string can still be "safely read back by the Lua
interpreter".

[1]: https://www.lua.org/manual/5.1/manual.html#pdf-string.format
[2]: https://github.com/lua/lua/commit/d62a21b9d379a576bae7426c80039ca1a4d2bb07
[3]: https://github.com/lua/lua/commit/658ea8752b979102627e2fede7b7ddfbb67ba6c9

This patch adapts test for LuaJIT and Lua 5.2 behaviour considering
the test from Lua 5.2 test suite taken from
https://www.lua.org/tests/lua-5.2.0-tests.tar.gz.

Resolves tarantool/tarantool#5710
Part of tarantool/tarantool#5845
Part of tarantool/tarantool#4473
---
 test/PUC-Rio-Lua-5.1-tests/strings.lua | 38 +++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/test/PUC-Rio-Lua-5.1-tests/strings.lua b/test/PUC-Rio-Lua-5.1-tests/strings.lua
index 237dbad3..0eee4c6e 100644
--- a/test/PUC-Rio-Lua-5.1-tests/strings.lua
+++ b/test/PUC-Rio-Lua-5.1-tests/strings.lua
@@ -102,7 +102,43 @@ print('+')
 
 x = '"ílo"\n\\'
 assert(string.format('%q%s', x, x) == '"\\"ílo\\"\\\n\\\\""ílo"\n\\')
-assert(string.format('%q', "\0") == [["\000"]])
+--[[
+LuaJIT: LuaJIT since v2.0.0-beta6 has extension from Lua 5.2:
+string.format(): %q reversible.
+
+The q option formats a string in a form suitable to be safely read
+back by the Lua interpreter [1].
+
+In Lua 5.1, '\0' was converted to "\000" unconditionally.
+
+In Lua 5.2, control characters are written as \nnn when needed,
+see d62a21b9d379a576bae7426c80039ca1a4d2bb07 ("when formatting
+with '%q', all control characters are coded as \nnn.") [1].
+In this patch, %q specifier starts writing control characters to
+a new string in the same way through \d, instead of their binary
+representation as it is. If the control character is followed by
+a digit, then for the correct work of the parser, it is necessary
+to extend the escape sequence to 3 significant characters
+(otherwise, the transition "\0002" -> "\02" corrupts string).
+For this patch, the expansion is performed unconditionally
+(the check for the next symbol is not performed) if this first
+symbol is a zero byte.
+
+Consistent work with the zero byte processing omitting the custom
+check was added in the commit
+658ea8752b979102627e2fede7b7ddfbb67ba6c9 ("no need to handle '\0'
+differently from other control chars in format '%q'") [2]. Note,
+that this patch does not change the semantics of %q specifier -
+the new string can still be "safely read back by the Lua
+interpreter".
+
+[1]: https://www.lua.org/manual/5.1/manual.html#pdf-string.format
+[2]: https://github.com/lua/lua/commit/d62a21b9d379a576bae7426c80039ca1a4d2bb07
+[3]: https://github.com/lua/lua/commit/658ea8752b979102627e2fede7b7ddfbb67ba6c9
+
+Test is adapted from PUC-Rio Lua 5.2 test suite.
+--]]
+assert(string.format('%q', "\0") == [["\0"]])
 assert(string.format("\0%c\0%c%x\0", string.byte("á"), string.byte("b"), 140) ==
               "\0á\0b8c\0")
 assert(string.format('') == "")
-- 
2.31.0