#4388 direct eval [expr] not NRE safe (Tcl_ExprObj)

[Don Porter]

% coroutine foo apply {{} {set expr expr; $expr {[yield]}}}
cannot yield: C stack busy

I think this also causes trouble in the expression
evaluation portion of direct eval [for] and [while]
commands.

[Donal K. Fellows]

There's no TclNRExpr() API or equivalent, so fixing this requires substantial work. Assigning to person better suited than me to carry this out.

[Don Porter]

Patch under construction.

[Don Porter]

Needs some more refinement but here's
a first functional patch that fixes the bug.

[Don Porter]

Here's a cleaned up patch to review.

There are still a couple of TODO's
regarding a more careful audit of where
the interp state should be saved/reset/restored,
but the big picture is right now, and better
commented.

Also missing is docs and the TIP
for the new public routine
Tcl_NRExprObj().

[Don Porter]

[Don Porter]

Latest patch includes updates to docs.

[Don Porter]

Patch / TIP 353 committed to HEAD.

Still open while I check on the [for], [while] claims.

[Don Porter]

Patching up the callers of Tcl_ExprBooleanObj()
is better tracked in Bug 2823276.