QString::isLower/isUpper: redo the implementation

Use QStringIterator rather than indexed loops. This fixes handling of
non-BMP code points (which may be lower or uppercase, see the test).

Change also the semantics of the functions, adopting Unicode §3.13
definitions: a string is lowercase/uppercase if it's equal to its
own toLower/toUpper folding.

As a side effect, empty strings are now correctly reported to be
lowercase AND uppercase.

[ChangeLog][Important Behavior Changes] The semantics of
QString::isLower() and QString::isUpper() have been changed to match the
Unicode specification. Now lowercase (resp. uppercase) strings are
allowed to contain any character; a string is considered lowercase
(resp. uppercase) if it's equal to its own toLower() (resp. toUpper())
folding.  Previously, a non-letter character would make the string not
lowercase nor uppercase, and the mere presence of an uppercase (resp.
lowercase) letter would make isLower() (resp. isUpper()) return false,
even if the letter wouldn't change under case folding.  As a
consequence, now empty strings are lowercase and uppercase.

[ChangeLog][QtCore][QString] Fixed a number of bugs of
QString::isLower() and QString::isUpper(). Empty strings are now
correctly reported to be lowercase (resp. uppercase), and strings
containing code points outside the BMP are now correctly handled.
Note that the behavior of these functions has also been changed.

Change-Id: Iba1398279a072399a9f21295fe75f6e414f3f813
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 26 insertions, 18 deletions

diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index b929786255..fa8b5cf3f8 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -5109,21 +5109,25 @@ bool QString::endsWith(QChar c, Qt::CaseSensitivity cs) const
 }
 
 /*!
-    Returns \c true if the string only contains uppercase letters,
-    otherwise returns \c false.
+    Returns \c true if the string is uppercase, that is, it's identical
+    to its toUpper() folding.
+
+    Note that this does \e not mean that the string does not contain
+    lowercase letters (some lowercase letters do not have a uppercase
+    folding; they are left unchanged by toUpper()).
+    For more information, refer to the Unicode standard, section 3.13.
+
     \since 5.12
 
-    \sa QChar::isUpper(), isLower()
+    \sa QChar::toUpper(), isLower()
 */
 bool QString::isUpper() const
 {
-    if (isEmpty())
-        return false;
+    QStringIterator it(*this);
 
-    const QChar *d = data();
-
-    for (int i = 0, max = size(); i < max; ++i) {
-        if (!d[i].isUpper())
+    while (it.hasNext()) {
+        uint uc = it.nextUnchecked();
+        if (qGetProp(uc)->cases[QUnicodeTables::UpperCase].diff)
             return false;
     }
 
@@ -5131,21 +5135,25 @@ bool QString::isUpper() const
 }
 
 /*!
-    Returns \c true if the string only contains lowercase letters,
-    otherwise returns \c false.
+    Returns \c true if the string is lowercase, that is, it's identical
+    to its toLower() folding.
+
+    Note that this does \e not mean that the string does not contain
+    uppercase letters (some uppercase letters do not have a lowercase
+    folding; they are left unchanged by toLower()).
+    For more information, refer to the Unicode standard, section 3.13.
+
     \since 5.12
 
-    \sa QChar::isLower(), isUpper()
+    \sa QChar::toLower(), isUpper()
  */
 bool QString::isLower() const
 {
-    if (isEmpty())
-        return false;
+    QStringIterator it(*this);
 
-    const QChar *d = data();
-
-    for (int i = 0, max = size(); i < max; ++i) {
-        if (!d[i].isLower())
+    while (it.hasNext()) {
+        uint uc = it.nextUnchecked();
+        if (qGetProp(uc)->cases[QUnicodeTables::LowerCase].diff)
             return false;
     }