QLocale: Add option to pad numbers with trailing zeroes

EcmaScript mandates that number-to-string functions pad the resulting
strings with zeroes, up to the requested precision. QLocale actually
supports this, under the disguise of the "Alternate" flag, used by
QString::asprintf().

We split this flag into the three options it actually represents and
make IncludeTrailingZeroesAfterDot available as a NumberOption. This
allows us to generate numbers in an EcmaScript compliant way.

In addition, a symmetrical option to reject trailing zeroes when
parsing strings to numbers is added.

[ChangeLog][QtCore][QLocale] Additional flags in QLocale::NumberOption
allow generating strings from doubles in accordance to EcmaScript's
Number.toPrecision(n).

Change-Id: If1090d5a0364a29811011a472afc8b75d0af0a8f
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

6 files changed, 76 insertions, 38 deletions

diff --git a/src/corelib/io/qtextstream.cpp b/src/corelib/io/qtextstream.cpp
index b8db23329a..80df3a12e1 100644
--- a/src/corelib/io/qtextstream.cpp
+++ b/src/corelib/io/qtextstream.cpp
@@ -2547,6 +2547,7 @@ QTextStream &QTextStream::operator<<(double f)
     }
 
     uint flags = 0;
+    const QLocale::NumberOptions numberOptions = locale().numberOptions();
     if (numberFlags() & ShowBase)
         flags |= QLocaleData::ShowBase;
     if (numberFlags() & ForceSign)
@@ -2555,12 +2556,18 @@ QTextStream &QTextStream::operator<<(double f)
         flags |= QLocaleData::UppercaseBase;
     if (numberFlags() & UppercaseDigits)
         flags |= QLocaleData::CapitalEorX;
-    if (numberFlags() & ForcePoint)
-        flags |= QLocaleData::Alternate;
-    if (locale() != QLocale::c() && !(locale().numberOptions() & QLocale::OmitGroupSeparator))
+    if (numberFlags() & ForcePoint) {
+        flags |= QLocaleData::ForcePoint;
+
+        // Only for backwards compatibility
+        flags |= QLocaleData::AddTrailingZeroes | QLocaleData::ShowBase;
+    }
+    if (locale() != QLocale::c() && !(numberOptions & QLocale::OmitGroupSeparator))
         flags |= QLocaleData::ThousandsGroup;
-    if (!(locale().numberOptions() & QLocale::OmitLeadingZeroInExponent))
+    if (!(numberOptions & QLocale::OmitLeadingZeroInExponent))
         flags |= QLocaleData::ZeroPadExponent;
+    if (numberOptions & QLocale::IncludeTrailingZeroesAfterDot)
+        flags |= QLocaleData::AddTrailingZeroes;
 
     const QLocaleData *dd = d->locale.d->m_data;
     QString num = dd->doubleToString(f, d->params.realNumberPrecision, form, -1, flags);
diff --git a/src/corelib/tools/qlocale.cpp b/src/corelib/tools/qlocale.cpp
index 7809c513d6..c25ee5ffbe 100644
--- a/src/corelib/tools/qlocale.cpp
+++ b/src/corelib/tools/qlocale.cpp
@@ -2024,6 +2024,8 @@ QString QLocale::toString(double i, char f, int prec) const
         flags |= QLocaleData::ThousandsGroup;
     if (!(d->m_numberOptions & OmitLeadingZeroInExponent))
         flags |= QLocaleData::ZeroPadExponent;
+    if (d->m_numberOptions & IncludeTrailingZeroesAfterDot)
+        flags |= QLocaleData::AddTrailingZeroes;
     return d->m_data->doubleToString(i, prec, form, -1, flags);
 }
 
@@ -2785,7 +2787,7 @@ QString QLocaleData::doubleToString(const QChar _zero, const QChar plus, const Q
                 reinterpret_cast<ushort *>(digits.data())[i] += z;
         }
 
-        bool always_show_decpt = (flags & Alternate || flags & ForcePoint);
+        bool always_show_decpt = (flags & ForcePoint);
         switch (form) {
             case DFExponent: {
                 num_str = exponentForm(_zero, decimal, exponential, group, plus, minus,
@@ -2800,7 +2802,7 @@ QString QLocaleData::doubleToString(const QChar _zero, const QChar plus, const Q
                 break;
             }
             case DFSignificantDigits: {
-                PrecisionMode mode = (flags & Alternate) ?
+                PrecisionMode mode = (flags & AddTrailingZeroes) ?
                             PMSignificantDigits : PMChopTrailingZeros;
 
                 int cutoff = precision < 0 ? 6 : precision;
@@ -2905,7 +2907,7 @@ QString QLocaleData::longLongToString(const QChar zero, const QChar group,
     for (int i = num_str.length()/* - cnt_thousand_sep*/; i < precision; ++i)
         num_str.prepend(base == 10 ? zero : QChar::fromLatin1('0'));
 
-    if ((flags & Alternate || flags & ShowBase)
+    if ((flags & ShowBase)
             && base == 8
             && (num_str.isEmpty() || num_str[0].unicode() != QLatin1Char('0')))
         num_str.prepend(QLatin1Char('0'));
@@ -2926,10 +2928,10 @@ QString QLocaleData::longLongToString(const QChar zero, const QChar group,
             --num_pad_chars;
 
         // leave space for optional '0x' in hex form
-        if (base == 16 && (flags & Alternate || flags & ShowBase))
+        if (base == 16 && (flags & ShowBase))
             num_pad_chars -= 2;
         // leave space for optional '0b' in binary form
-        else if (base == 2 && (flags & Alternate || flags & ShowBase))
+        else if (base == 2 && (flags & ShowBase))
             num_pad_chars -= 2;
 
         for (int i = 0; i < num_pad_chars; ++i)
@@ -2939,9 +2941,9 @@ QString QLocaleData::longLongToString(const QChar zero, const QChar group,
     if (flags & CapitalEorX)
         num_str = num_str.toUpper();
 
-    if (base == 16 && (flags & Alternate || flags & ShowBase))
+    if (base == 16 && (flags & ShowBase))
         num_str.prepend(QLatin1String(flags & UppercaseBase ? "0X" : "0x"));
-    if (base == 2 && (flags & Alternate || flags & ShowBase))
+    if (base == 2 && (flags & ShowBase))
         num_str.prepend(QLatin1String(flags & UppercaseBase ? "0B" : "0b"));
 
     // add sign
@@ -2988,7 +2990,7 @@ QString QLocaleData::unsLongLongToString(const QChar zero, const QChar group,
     for (int i = num_str.length()/* - cnt_thousand_sep*/; i < precision; ++i)
         num_str.prepend(base == 10 ? zero : QChar::fromLatin1('0'));
 
-    if ((flags & Alternate || flags & ShowBase)
+    if ((flags & ShowBase)
             && base == 8
             && (num_str.isEmpty() || num_str[0].unicode() != QLatin1Char('0')))
         num_str.prepend(QLatin1Char('0'));
@@ -3003,10 +3005,10 @@ QString QLocaleData::unsLongLongToString(const QChar zero, const QChar group,
         int num_pad_chars = width - num_str.length();
 
         // leave space for optional '0x' in hex form
-        if (base == 16 && flags & Alternate)
+        if (base == 16 && flags & ShowBase)
             num_pad_chars -= 2;
         // leave space for optional '0b' in binary form
-        else if (base == 2 && flags & Alternate)
+        else if (base == 2 && flags & ShowBase)
             num_pad_chars -= 2;
 
         for (int i = 0; i < num_pad_chars; ++i)
@@ -3016,9 +3018,9 @@ QString QLocaleData::unsLongLongToString(const QChar zero, const QChar group,
     if (flags & CapitalEorX)
         num_str = num_str.toUpper();
 
-    if (base == 16 && (flags & Alternate || flags & ShowBase))
+    if (base == 16 && flags & ShowBase)
         num_str.prepend(QLatin1String(flags & UppercaseBase ? "0X" : "0x"));
-    else if (base == 2 && (flags & Alternate || flags & ShowBase))
+    else if (base == 2 && flags & ShowBase)
         num_str.prepend(QLatin1String(flags & UppercaseBase ? "0B" : "0b"));
 
     // add sign
@@ -3079,25 +3081,37 @@ bool QLocaleData::numberToCLocale(const QChar *str, int len, QLocale::NumberOpti
                 out = in.toLatin1();
             else
                 break;
+        } else if (out == '.') {
+            // Fail if more than one decimal point or point after e
+            if (decpt_idx != -1 || exponent_idx != -1)
+                return false;
+            decpt_idx = idx;
+        } else if (out == 'e' || out == 'E') {
+            exponent_idx = idx;
         }
 
         if (number_options & QLocale::RejectLeadingZeroInExponent) {
-            if (out == 'e' || out == 'E') {
-                exponent_idx = idx;
-            } else if (exponent_idx != -1) {
-                if (out >= '1' && out <= '9')
-                    exponent_idx = -1; // leading digit is not 0, forget exponent_idx
-                else if (out == '0' && idx < l - 1)
+            if (exponent_idx != -1 && out == '0' && idx < l - 1) {
+                // After the exponent there can only be '+', '-' or digits.
+                // If we find a '0' directly after some non-digit, then that is a leading zero.
+                if (result->last() < '0' || result->last() > '9')
                     return false;
             }
         }
 
+        if (number_options & QLocale::RejectTrailingZeroesAfterDot) {
+            // If we've seen a decimal point and the last character after the exponent is 0, then
+            // that is a trailing zero.
+            if (decpt_idx >= 0 && idx == exponent_idx && result->last() == '0')
+                    return false;
+        }
+
         if (!(number_options & QLocale::RejectGroupSeparator)) {
             if (start_of_digits_idx == -1 && out >= '0' && out <= '9') {
                 start_of_digits_idx = idx;
             } else if (out == ',') {
-                // Don't allow group chars after the decimal point
-                if (decpt_idx != -1)
+                // Don't allow group chars after the decimal point or exponent
+                if (decpt_idx != -1 || exponent_idx != -1)
                     return false;
 
                 // check distance from the last separator or from the beginning of the digits
@@ -3114,12 +3128,6 @@ bool QLocaleData::numberToCLocale(const QChar *str, int len, QLocale::NumberOpti
                 ++idx;
                 continue;
             } else if (out == '.' || out == 'e' || out == 'E') {
-                // Fail if more than one decimal point
-                if (out == '.' && decpt_idx != -1)
-                    return false;
-                if (decpt_idx == -1)
-                    decpt_idx = idx;
-
                 // check distance from the last separator
                 // ### FIXME: Some locales allow other groupings! See https://en.wikipedia.org/wiki/Thousands_separator
                 if (last_separator_idx != -1 && idx - last_separator_idx != 4)
@@ -3145,6 +3153,12 @@ bool QLocaleData::numberToCLocale(const QChar *str, int len, QLocale::NumberOpti
             return false;
     }
 
+    if (number_options & QLocale::RejectTrailingZeroesAfterDot) {
+        // In decimal form, the last character can be a trailing zero if we've seen a decpt.
+        if (decpt_idx != -1 && exponent_idx == -1 && result->last() == '0')
+            return false;
+    }
+
     result->append('\0');
     return idx == l;
 }
diff --git a/src/corelib/tools/qlocale.h b/src/corelib/tools/qlocale.h
index 657fce9fa1..bd89e48234 100644
--- a/src/corelib/tools/qlocale.h
+++ b/src/corelib/tools/qlocale.h
@@ -897,7 +897,9 @@ public:
         OmitGroupSeparator = 0x01,
         RejectGroupSeparator = 0x02,
         OmitLeadingZeroInExponent = 0x04,
-        RejectLeadingZeroInExponent = 0x08
+        RejectLeadingZeroInExponent = 0x08,
+        IncludeTrailingZeroesAfterDot = 0x10,
+        RejectTrailingZeroesAfterDot = 0x20
     };
     Q_DECLARE_FLAGS(NumberOptions, NumberOption)
 
diff --git a/src/corelib/tools/qlocale.qdoc b/src/corelib/tools/qlocale.qdoc
index f4b49095df..88b071e161 100644
--- a/src/corelib/tools/qlocale.qdoc
+++ b/src/corelib/tools/qlocale.qdoc
@@ -969,7 +969,8 @@
     setNumberOptions().
 
     \value DefaultNumberOptions This option represents the default behavior, with
-            group separators and with one leading zero in single digit exponents.
+            group separators, with one leading zero in single digit exponents, and
+            without trailing zeroes after the decimal dot.
     \value OmitGroupSeparator If this option is set, the number-to-string functions
             will not insert group separators in their return values. The default
             is to insert group separators.
@@ -984,6 +985,14 @@
             functions will fail if they encounter an exponent padded with zeroes when
             parsing a floating point number in scientific notation. The default is to
             accept such padding.
+    \value IncludeTrailingZeroesAfterDot If this option is set, the number-to-string
+            functions will pad numbers with zeroes to the requested precision in "g"
+            or "most concise" mode, even if the number of significant digits is lower
+            than the requested precision. The default is to omit trailing zeroes.
+    \value RejectTrailingZeroesAfterDot If this option is set, the string-to-number
+            functions will fail if they encounter trailing zeroes after the decimal
+            dot when parsing a number in scientific or decimal representation. The
+            default is to accept trailing zeroes.
 
     \sa setNumberOptions(), numberOptions()
 */
diff --git a/src/corelib/tools/qlocale_p.h b/src/corelib/tools/qlocale_p.h
index c83c9d3333..74d8e5f381 100644
--- a/src/corelib/tools/qlocale_p.h
+++ b/src/corelib/tools/qlocale_p.h
@@ -193,7 +193,7 @@ public:
 
     enum Flags {
         NoFlags             = 0,
-        Alternate           = 0x01,
+        AddTrailingZeroes   = 0x01,
         ZeroPadded          = 0x02,
         LeftAdjusted        = 0x04,
         BlankBeforePositive = 0x08,
@@ -204,7 +204,7 @@ public:
         ShowBase            = 0x80,
         UppercaseBase       = 0x100,
         ZeroPadExponent     = 0x200,
-        ForcePoint          = Alternate
+        ForcePoint          = 0x400
     };
 
     enum NumberMode { IntegerMode, DoubleStandardMode, DoubleScientificMode };
diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index dab91ae0a0..942df9e0dd 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -5908,7 +5908,10 @@ static uint parse_flag_characters(const char * &c) Q_DECL_NOTHROW
     uint flags = QLocaleData::ZeroPadExponent;
     while (true) {
         switch (*c) {
-        case '#': flags |= QLocaleData::Alternate; break;
+        case '#':
+            flags |= QLocaleData::ShowBase | QLocaleData::AddTrailingZeroes
+                    | QLocaleData::ForcePoint;
+            break;
         case '0': flags |= QLocaleData::ZeroPadded; break;
         case '-': flags |= QLocaleData::LeftAdjusted; break;
         case ' ': flags |= QLocaleData::BlankBeforePositive; break;
@@ -6166,7 +6169,7 @@ QString QString::vasprintf(const char *cformat, va_list ap)
             case 'p': {
                 void *arg = va_arg(ap, void*);
                 const quint64 i = reinterpret_cast<quintptr>(arg);
-                flags |= QLocaleData::Alternate;
+                flags |= QLocaleData::ShowBase;
                 subst = QLocaleData::c()->unsLongLongToString(i, precision, 16, width, flags);
                 ++c;
                 break;
@@ -7741,10 +7744,13 @@ QString QString::arg(double a, int fieldWidth, char fmt, int prec, QChar fillCha
     if (d.locale_occurrences > 0) {
         QLocale locale;
 
-        if (!(locale.numberOptions() & QLocale::OmitGroupSeparator))
+        const QLocale::NumberOptions numberOptions = locale.numberOptions();
+        if (!(numberOptions & QLocale::OmitGroupSeparator))
             flags |= QLocaleData::ThousandsGroup;
-        if (!(locale.numberOptions() & QLocale::OmitLeadingZeroInExponent))
+        if (!(numberOptions & QLocale::OmitLeadingZeroInExponent))
             flags |= QLocaleData::ZeroPadExponent;
+        if (numberOptions & QLocale::IncludeTrailingZeroesAfterDot)
+            flags |= QLocaleData::AddTrailingZeroes;
         locale_arg = locale.d->m_data->doubleToString(a, prec, form, fieldWidth, flags);
     }