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There are 3 builtin case conversion string functions: upper(), lower(),
and initcap(). Previously they only convert English alphabetic
characters. This patch adds support to deal with Unicode characters.
There are many corner cases in case conversion depending on the locale
and context. E.g.
1) Case conversion is locale-sensitive.
Turkish has 4 letter "I"s. English has only two, a lowercase dotted i
and an uppercase dotless I. Turkish has lowercase and uppercase forms of
both dotted and dotless I. So simply converting "i" to "I" for upper
case is wrong in Turkish:
+-------+--------+---------+
| | Dotted | Dotless |
+-------+--------+---------+
| Upper | İ | I |
+-------+--------+---------+
| Lower | i | ı |
+-------+--------+---------+
2) Case conversion may change a string's length.
The German word "grüßen" should be converted to "GRÜSSEN" in upper case:
the letter "ß" should be converted to "SS".
3) Case conversion is context-sensitive.
The Greek word "ὈΔΥΣΣΕΎΣ" should be converted to "ὀδυσσεύς", where the
Greek letter "Σ" is converted to "σ" or to "ς", depending on its
position in the word.
The above cases will be focus in follow-up JIRAs. This patch addes the
initial implementation of UTF-8 aware case conversion functions.
--------
Implementation:
In UTF-8 mode (turned on by set UTF8_MODE=true) of these functions, the
bytes in strings are converted to wide characters using std::mbrtowc().
Each wide character (wchar_t) will then be converted using std::towupper
or std::towlower correspondingly. We then convert them back to multi
bytes using std::wcrtomb().
Note that these builtins are locale aware. If impalad is launched
without a UTF-8 aware locale, e.g. LC_ALL="C", these builtins can't
recognize non-ascii characters, which will return unexpected results.
Thus we modify our docker images to set LC_ALL="C.UTF-8" instead of "C".
This patch also logs the current locale when launching impala daemons
for better debugging. We will support customized locale in IMPALA-11080.
Test:
- Add BE unit tests and e2e tests.
Change-Id: I443e89d46f4638ce85664b021666bc4f03ee8abd
Reviewed-on: http://gerrit.cloudera.org:8080/17785
Reviewed-by: Csaba Ringhofer <csringhofer@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>