[Tcl-bugs] [ tcl-Bugs-3610400 ] tailcall clashes with execution traces

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Bugs item #3610400, was opened at 2013-04-09 11:05
Message generated for change (Tracker Item Submitted) made by dgp
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Category: 60. NRE and coroutines
Group: current: 8.6.0
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Don Porter (dgp)
Assigned to: miguel sofer (msofer)
Summary: tailcall clashes with execution traces

Initial Comment:

working on 3610393, I constructed this script to
see how ensemble redirections play with execution
traces, and found an issue with [tailcall]:

namespace eval foo {
    namespace export *
    proc target {} {puts Hit!}
    proc bar {} {tailcall target}
    namespace ensemble create
}
proc harness {} {
    foo target
    foo bar
}
proc handle {cmd args} {
    puts "Command [lindex $cmd 0] resolves to:"
    puts "\t'[uplevel 1 [list ::namespace which -command [lindex $cmd 0]]]'"
    puts "\t\tResolved at level [uplevel 1 {info level}]"
}
trace add execution harness enterstep handle
harness


Output:

Command foo resolves to:
        '::foo'
                Resolved at level 1
Command ::foo::target resolves to:
        '::foo::target'
                Resolved at level 1
Command puts resolves to:
        '::puts'
                Resolved at level 2
Hit!
Command foo resolves to:
        '::foo'
                Resolved at level 1
Command ::foo::bar resolves to:
        '::foo::bar'
                Resolved at level 1
Command tailcall resolves to:
        '::tailcall'
                Resolved at level 2
Command target resolves to:
        ''
                Resolved at level 1
Command puts resolves to:
        '::puts'
                Resolved at level 2
Hit!

The commonality with oo forwards is that
tailcall also causes command name resolution
to be done early, in a context that may/does not
appear in a stack frame at the time the command
execution (and its execution traces) fire.

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