install: derive tclsh from --with-tcl when --with-tclsh is not set

When Tcl is installed in a non-default location, the extension library
is built against the tclConfig.sh designated by --with-tcl whereas the
installed scripts run with the first tclsh found in PATH unless
--with-tclsh is also passed. Such mismatch is not reported at build time
and only shows up later through a library load failure or behavior
differences.

Look for the Tcl interpreter shell in the Tcl installation designated by
--with-tcl before searching PATH: in the bin directory of the exec prefix
recorded in tclConfig.sh, or in the bin directory sibling to the
directory holding this script when it cannot be read. A version-suffixed
tclsh is tried first as some installations do not provide the generic
name. If no interpreter is found there, a warning is reported and the
PATH lookup applies. An explicit --with-tclsh still takes precedence so
both options can be decoupled when needed.

The version-specific names tried by the PATH lookup now cover Tcl 9.0
and no longer Tcl 8.4, which is not supported anymore.

Fixes #717

Assisted-by: Claude:claude-fable-5-1
Signed-off-by: Xavier Delaruelle <xavier.delaruelle@cea.fr>

Author: xdelaruelle

INSTALL.rst

@@ -1596,6 +1596,21 @@ instance :instopt:`--without-modulepath<--with-modulepath>`):
  compile Modules Tcl extension library if this file cannot be automatically
  found in default locations.
 
+ Unless :instopt:`--with-tclsh` is set, the Tcl interpreter shell is also
+ looked for in the Tcl installation designated by this option: ``tclsh`` is
+ searched in the ``bin`` directory of the installation prefix recorded in
+ ``tclConfig.sh`` (or in the ``bin`` directory sibling of the directory
+ holding this script when it cannot be read). This way :file:`modulecmd.tcl`
+ and other installed scripts run with the same Tcl the extension library is
+ built against. If no interpreter shell is found there, a warning is reported
+ and ``tclsh`` is looked for in standard binary paths.
+
+ .. only:: html or latex
+
+    .. versionchanged:: 5.8
+       Tcl interpreter shell is looked for in designated Tcl installation
+       unless :instopt:`--with-tclsh` is set
+
 .. instopt:: --with-tclinclude
 
  Directory containing the Tcl header files. Useful to compile Modules Tcl
@@ -1606,10 +1621,20 @@ instance :instopt:`--without-modulepath<--with-modulepath>`):
 
  Name or full path of Tcl interpreter shell (default=\ ``tclsh``)
 
+ When this option is not set, ``tclsh`` is looked for in the Tcl installation
+ designated by :instopt:`--with-tcl` if this option is set, then in standard
+ binary paths. Set this option to decouple the interpreter shell running the
+ installed scripts from the Tcl installation the extension library is built
+ against.
+
  .. only:: html or latex
 
     .. versionadded:: 4.0
 
+    .. versionchanged:: 5.8
+       Default interpreter shell is looked for in the Tcl installation
+       designated by :instopt:`--with-tcl`
+
 .. instopt:: --with-tcl-linter=BIN
 
  Name or full path of program to use to lint modulefile through the

NEWS.rst

@@ -6,6 +6,17 @@ Release notes
 This file describes changes in recent versions of Modules. It primarily
 documents those changes that are of interest to users and admins.
 
+.. _5.8 release notes:
+
+Modules 5.8.0 (not yet released)
+--------------------------------
+
+* Install: look for the Tcl interpreter shell in the Tcl installation
+  designated by :instopt:`--with-tcl` when :instopt:`--with-tclsh` is not set,
+  so that installed scripts run with the same Tcl the extension library is
+  built against. (fix issue #717)
+
+
 .. _5.7 release notes:
 
 Modules 5.7.0 (2026-09-21)

configure

@@ -88,6 +88,7 @@ pathentryreorder=n
 loadedmodules=
 quarantinevars=
 binsearchpath=/usr/bin:/bin:/usr/local/bin
+tcldir=
 TCLSH=tclsh
 PYTHON=python
 SPHINXBUILD=sphinx-build
@@ -522,13 +523,16 @@ Optional Packages:
                           TAGLIST is a tag name or abbreviation (elements in
                           TAGLIST are separated by \`:') [$tagcolorname]
   --with-tcl              directory containing the Tcl configuration script
-                          tclConfig.sh.
+                          tclConfig.sh. Tcl interpreter shell is also looked
+                          for in this Tcl installation (see --with-tclsh).
   --with-tcl-linter=BIN   name of full path of program to use to lint Tcl
                           modulefiles [$tcllinter]
   --with-tcl-linter-opts=OPTLIST
                           settings to apply to tcl linter program [$tcllinteropts]
   --with-tclinclude       directory containing the Tcl header files.
-  --with-tclsh=BIN        name or full path of Tcl interpreter shell [tclsh]
+  --with-tclsh=BIN        name or full path of Tcl interpreter shell. Unless
+                          set, tclsh is looked for in the Tcl installation
+                          designated by --with-tcl then in PATH [tclsh]
   --with-terminal-background=VALUE
                           terminal background color which determines the color
                           set to apply by default between the \`dark' background
@@ -611,6 +615,13 @@ check_requirement() {
    fi
 }
 
+# get value of a variable defined in Tcl configuration script
+get_tclconfig_value() {
+   # source script in a subshell to keep its variables out of our environment
+   # shellcheck disable=SC1090
+   (. "$1" >/dev/null 2>&1; echo "${!2}")
+}
+
 # parse optional argument to find if feature is enabled or disabled
 get_feature_value() {
    typeset val="${1#*=}"
@@ -986,7 +997,10 @@ for arg in "$@"; do
    --with-tcl-linter-opts=*|--without-tcl-linter-opts)
       # shellcheck disable=SC2034
       tcllinteropts=$(get_package_value "$arg" "") ;;
-   --with-tcl=*|--without-tcl|--with-tclinclude=*|--without-tclinclude)
+   --with-tcl=*|--without-tcl)
+      tcldir=$(get_package_value "$arg")
+      libarglist+=("$arg") ;;
+   --with-tclinclude=*|--without-tclinclude)
       libarglist+=("$arg") ;;
    --with-python=*|--without-python)
       pythonbin=$(get_package_value "$arg") ;;
@@ -1112,8 +1126,46 @@ fi
 if [ -n "$tclshbin" ]; then
    check_requirement "$tclshbin" '' "PATH=$binsearchpath"
 else
-   # also check version-specific names in case no generic tclsh binary exists
-   check_requirement $TCLSH '' "PATH=$binsearchpath" 'tclsh8.6' 'tclsh8.5' 'tclsh8.4'
+   reqpath=''
+   # look first in the Tcl installation designated by --with-tcl, so that
+   # installed scripts run with the Tcl the extension library is built
+   # against rather than with whatever tclsh comes first in PATH
+   if [ -n "$tcldir" ]; then
+      # accept tclConfig.sh file path like extension library configure does
+      tcldir=${tcldir%/tclConfig.sh}
+      # the configuration script records where Tcl binaries are installed and
+      # the version suffix of the interpreter shell
+      if [ -f "$tcldir/tclConfig.sh" ]; then
+         tclexecprefix=$(get_tclconfig_value "$tcldir/tclConfig.sh" \
+            TCL_EXEC_PREFIX)
+         tclversion=$(get_tclconfig_value "$tcldir/tclConfig.sh" TCL_VERSION)
+      else
+         tclexecprefix=''
+         tclversion=''
+      fi
+      if [ -n "$tclexecprefix" ]; then
+         tclbinsearchpath="$tclexecprefix/bin"
+      else
+         # assume tclConfig.sh lies in a lib directory sibling to bin
+         tclbinsearchpath=$(cd "$tcldir/../bin" 2>/dev/null && pwd \
+            || echo "$tcldir/../bin")
+      fi
+      if [ -n "$tclversion" ]; then
+         check_requirement "tclsh$tclversion" '-' "PATH=$tclbinsearchpath" \
+            'tclsh'
+      else
+         check_requirement 'tclsh' '-' "PATH=$tclbinsearchpath" 'tclsh9.0' \
+            'tclsh8.6' 'tclsh8.5'
+      fi
+      if [ -z "$reqpath" ]; then
+         echo_warning "No Tcl interpreter shell found in \`$tclbinsearchpath' \
+from Tcl installation designated by \`--with-tcl', looking in standard PATHs"
+      fi
+   fi
+   if [ -z "$reqpath" ]; then
+      # also check version-specific names in case no generic tclsh binary exists
+      check_requirement $TCLSH '' "PATH=$binsearchpath" 'tclsh9.0' 'tclsh8.6' 'tclsh8.5'
+   fi
 fi
 TCLSH=$reqpath