magicexec.c, magicdnull.c and tclmagic.c hardwired the compile-time TCL_DIR
(the install location) when locating magic.tcl (tcl_rcFileName) and the Tcl
auto_path. So even with CAD_ROOT set -- the documented relocation knob, already
honored by the sys-file search and by tcltk/magic.sh's
TCL_MAG_DIR=${CAD_ROOT}/magic/tcl -- the C launchers still looked in the baked
install path, which is why magic could not source its startup from a relocated
install or a build tree.
Add tcltk/tcldir.h with a MagicTclDir() helper: $CAD_ROOT/magic/tcl when CAD_ROOT
is set and non-empty, else the compile-time TCL_DIR. Use it in all three sites.
This makes the C side consistent with the shell wrappers and with how magic.tcl
itself already derives its own directory (from `info script`).
Verified: default (no CAD_ROOT) resolves to TCL_DIR as before (build rc=0); with
CAD_ROOT pointed at a staged build tree, `magicdnull -dnull` sources magic.tcl
from there and runs (tech load scmos -> 13 planes).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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