highlight net does not incoporate new connections

[Thomas Pointhuber]

# HowTo reproduce

1. highlight some net in eeschema
2. extend the highlighted net with a new wire

It is expected that the new wire is also highlighted, but it stays in its default color

# Version Information

Application: kicad
Version: (6.0.0-rc1-dev-1009-g96e65c7f2), debug build
Libraries:
    wxWidgets 3.1.1
    libcurl/7.61.1 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.4) libssh2/1.8.0 nghttp2/1.34.0
Platform: Linux 4.18.16-arch1-1-ARCH x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.1.1 (wchar_t,wx containers) GTK+ 2.24
    Boost: 1.68.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.61.1
    Compiler: Clang 7.0.0 with C++ ABI 1002

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=OFF
    KICAD_SCRIPTING_WXPYTHON=OFF
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

[Jon Evans (craftyjon)]

Jeff, FYI I haven't looked at this problem, but thinking about it very quickly, it seems possible that when you are extending a highlighted net with new wires, the highlighted net name could change (for example if the new wires connect to a higher-priority label) so that will need to be considered in the fix.

[Jeff Young (jeyjey)]

@Jon, I'm not sure the correct answer is always to change it. Let's say you highlight "Chassis GND" and then see a connection that ought to go to "Audio GND". If you correct the bad connection, you don't want the highlighting to change to "Audio GND"; you probably want it to stay "Chassis GND".

Maybe we could only update the name when it no longer exists (that is a higher-priority label /completely/ replaced a lower-priority name?

[Jeff Young (jeyjey)]

For now it keeps the named net but makes sure the highlighting is updated.

[Jon Evans (craftyjon)]

I think it's reasonable to only update when the prior no longer exists