[Qt-creator] Virtual functions resolving

[Orgad Shaneh]

Hello,

Following QTCREATORBUG-6067<https://bugreports.qt-project.org/browse/QTCREATORBUG-6067>
(navigation
in overrides/parents of a method), I'd like to suggest a new approach for
function overrides navigation.

I'll use the following snippet for reference. I'll try to make it as
minimal as possible:
class MostBasic
{
  virtual void v(); // 1
}

class Base : public MostBasic
{
  void v(); // 2
}

class Derived : public Base {}

class MostDerived : public Derived
{
  void v(); // 3
}

void foo()
{
  MostBasic().v(); // 4
  Base().v(); // 5
  Derived().v(); // 6
  MostDerived().v(); // 7
}

I'll divide the discussion into 2 use-cases:
1. Find Usages
2. Follow Symbol

0. Currently Find Usages mixes usages (references) with declarations. This
is mostly useful for renames. When users (at least me and some people I
asked :)) look for usages, they usually are not interested in declarations.
To address this, I suggest adding a combobox in the C++ Usages search pane
that will filter 'Declarations', 'Usages' or 'All'. The pane could be
renamed respectively (C++ References? C++ Symbols?)

1. Conceptually, when users call Find Usages, they want to know which calls
can reach this piece of code. For virtual functions, calls to 'lower' (i.e.
more concrete) types which implement the function, will not reach the
function in 'higher' types.
For example, Find Usages on Base::v (usages only, we'll leave declarations
for later) should only list entries 4 and 5 and 6. 7 is not calling Base::v
since it is reimplemented in MostDerived.

2. Follow Symbol has complementary behavior. Conceptually, following a
symbol means 'where will this call lead?'. Again, for virtual functions the
answer is complex, since a call for a basic type can lead to a more
concrete type.
For example, Follow Symbol on entries 5 or 6 (here referring to
declarations) should list entries 2 and 3, but not 1, since a call to Base,
which implements v() itself, can not lead to MostBasic.
To address this, I suggest adding a new action which will open a C++ Usages
search pane with declarations only, containing only relevant entries.


Currently, handling function overrides doesn't seem to have high priority
(for example QTCREATORBUG-5876<https://bugreports.qt-project.org/browse/QTCREATORBUG-5876>
which
was a real pain! It was open for more than a year until I finally solved it
myself).

I'd like to hear your opinions on these issues. Are my suggestions
feasible? Would they require rewriting half of libcplusplus?

Thanks,
- Orgad
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