Qt-QStringArg

Check suspicious arg calls of QString and QLatin1String

Required inputs: IR

Implements three warnings:

1. Detects when you are using chained QString::arg() calls and should instead use the multi-arg overload to save memory allocations

   QString("%1 %2").arg(a).arg(b);
   QString("%1 %2").arg(a, b); // one less temporary heap allocation
   

2. Detects when you are passing an integer to QLatin1String::arg() as that gets implicitly cast to QChar. It's preferable to state your intention and cast to QChar explicitly.
3. Detects when you are using misleading QString::arg() overloads

   QString arg(qlonglong a, int fieldwidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(qulonglong a, int fieldwidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(long a, int fieldwidth = 0, int base=10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(ulong a, int fieldwidth = 0, int base=10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(int a, int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(uint a, int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(short a, int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(ushort a, int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const
   QString arg(double a, int fieldWidth = 0, char fmt = 'g', int prec = -1, QChar fillChar = QLatin1Char(' ')) const
   QString arg(char a, int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const
   QString arg(QChar a, int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const
   QString arg(const QString &a, int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const
   

   because they are commonly misused, for example:

   int hours = ...;
   int minutes = ...;
   // This will not do what you think it would at first glance.
   QString s("The time is %1:%2").arg(hours, minutes);
   

   To reduce false positives, some cases will not be warned about:

   str.arg(hours, 2); // User explicitly used a integer literal, this is probably fine
   str.arg(foo); // We are only after cases where the second argument (or further) is specified, so this is safe
   str.arg(foo, width); // Second argument is named width, or contains the name "width" or "count", this is safe.
   

   Using these misleading overloads may be perfectly valid but can be replaced by QString::asprintf. The message key misleading_qstring_arg may be disabled.

   The name to match the second argument may be configured by changing the option width_argument_name.

This rule is based on clazy rule qstring-arg

Possible Messages

Key	Text	Severity	Disabled
chained_arg_calls	Use multi-arg instead of chained arg calls.	None	False
implicit_qlatin1_cast	Argument passed to QLatin1String::arg() will be implicitly cast to QChar.	None	False
misleading_qstring_arg	QString::arg() used with fillChar overload.	None	False

Options

• This rule shares the following common options: exclude_in_macros, exclude_messages_in_system_headers, excludes, extend_exclude_to_macro_invocations, includes, justification_checker, languages, post_processing, provider, report_at, severity

• The following places define options that affect this rule: Stylechecks, Analysis-GlobalOptions

level

level : int = 0

Importance level of the rule as given for clazy. 0 is most desirable, higher values fall off in quality.

 

width_argument_name

width_argument_name : str = '.*(width|count).*'

If this case-insensitive regexp matches the name of the second argument of a misleading overload then the call is considered safe and not reported.