Improve regex for detecting OMZ function dependencies

[NigoroJr]

This change makes the pattern more strict so that expressions that are only in valid function call forms are added as dependencies. Valid forms of function use with examples are:

• func
  • func
• Leading or trailing whitespaces func
  • func 'foo'

• func\

  • Trailing backslash:

    func\
      'foo'

• (func)
  • foo=$(func)
• "func"
  • eval "func"
• 'func'
  • eval 'func'

• Surrounded by backquotes

  `func`
  
  Example:
  foo=`func`

  Problem Description

Error message:

update_terminalapp_cwd:4: command not found: omz_urlencode

Is shown before every prompt when using Terminal.app on a Mac OS X.

This is because lib/termsupport.zsh is considered a dependency of pip.plugin.zsh and is therefore sourced, adding update_terminalapp_cwd function to the precmd hook.

Environment

• Mac OS X 10.9.5 and 10.11.3
• Terminal.app bundled with the above versions
• zsh 5.2 and 5.0.8, respectively
• zplug 84bb580480bf6088fc025279d37c6ca41e1ffe39

  .zshrc

source $ZPLUG_HOME/init.zsh
zplug 'plugins/pip', \
    from:oh-my-zsh, \
    ignore:{oh-my-zsh.sh,plugins/pip/pip.plugin.zsh}, \
    nice:10

zplug check || zplug install
zplug load

Steps to Reproduce

1. Start a new zsh session

2. Observe the message:

   update_terminalapp_cwd:4: command not found: omz_urlencode

   Why this happens

plugins/pip/pip.plugin.zsh has a <title> HTML tag here. There is also a title function defined here. Since zplug only checks the presence of the function name in pip.plugin.zsh, it thinks that the function is being used and sources lib/termsupport.zsh.

Apart from this issue, maybe the check for dependency (i.e. call to __zplug::support::omz::depends) need to be after excluding files specified by the ignore tag, but this is a different issue.

What this PR fixes

In the example, it was <title> (an invalid form of function call) but from what I see it seems like foo_title_bar would also be considered a use of the title function. This PR fixes that scenario too. Valid function uses are described at the top and also in the commit message.

Checking

$ cat <<EOF | egrep "(^|\s|['\"(\`])func[0-9]($|\s|[\\\\'\")\`])"
func1
<func2>
 func3
func4\\
  bar
eval 'func5'
eval "func6 foo"
\`func7\`
foo_func8_bar
EOF
# Outputs:
# func1
#  func3
# func4\
# eval 'func5'
# eval "func6 foo"
# `func7`

[NigoroJr]

Thanks!