From d88c73d2067b2b426d1b5380dac46fcd62fb93ae Mon Sep 17 00:00:00 2001
From: Xavier Delaruelle <xavier.delaruelle@cea.fr>
Date: Sun, 26 Jul 2026 19:56:00 +0000
Subject: [PATCH] Avoid validating every sibling modulefile when resolving an
 exact version

findModules/findModulesFromDirsAndFiles now accept a 'stop_mod'
parameter: when set to an exact 'name/version' specification resolved
in a single-module context (load, display, is-avail, switch, ...), the
directory holding it is walked from the dictionary-highest to the
dictionary-lowest element, validating only what is needed to find the
first valid, non hidden element. This settles two things at once: this
is the directory's true implicit default/latest, and stop_mod is that
element or not. Listing commands (avail, whatis, search, ...) and bare
module name resolution are unaffected and keep validating every
sibling as before.

getModules sets 'stop_mod' whenever the query is an exact 'name/version'
specification (no wildcard, no result filtering), optionally with a
variant or an extra match search specifier, as long as the module name
and version part of it still resolves to a single, flat 'name/version'
element.

Add a new load3/load3_cache benchmark test to the mb script,
generating and removing its large sibling-version fixture on the fly.
Measured about 30 ms down to 19 ms (-36%) resolving one of 500 sibling
versions.

Add a new locate testsuite file covering invalid, hidden and
explicit-default-without-explicit-latest siblings, and a variant value
specified alongside the query, with its own fixture modulefiles.
Update two unrelated tests whose expected output depended on the exact
content of the shared modulepath directory used for these new
fixtures.

Closes #561

Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Xavier Delaruelle <xavier.delaruelle@cea.fr>
---
 .hunspell.en.dic                              |   3 +
 MIGRATING.rst                                 |  33 ++-
 NEWS.rst                                      |   7 +
 script/mb                                     |  79 +++++-
 tcl/modfind.tcl.in                            | 136 +++++++++-
 testsuite/mb/testenv_load3                    |   1 +
 testsuite/modulefiles.4/.modulerc             |   8 +
 testsuite/modulefiles.4/loc_fdv1/.modulerc    |   3 +
 testsuite/modulefiles.4/loc_fdv1/1.0          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.1          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.2          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.3          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.4          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.5          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.6          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.7          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.8          |   2 +
 testsuite/modulefiles.4/loc_fdv1/1.9          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.0          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.1          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.2          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.3          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.4          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.5          |   2 +
 testsuite/modulefiles.4/loc_fdv1/2.9          |   2 +
 testsuite/modulefiles.4/loc_fdv2/.version     |   3 +
 testsuite/modulefiles.4/loc_fdv2/1.0          |   2 +
 testsuite/modulefiles.4/loc_fdv2/1.1          |   2 +
 testsuite/modulefiles.4/loc_fdv2/1.2          |   2 +
 testsuite/modulefiles.4/loc_fdv2/1.3          |   2 +
 testsuite/modulefiles.4/loc_fdv2/1.4          |   2 +
 testsuite/modulefiles.4/loc_fdv2/1.5          |   2 +
 testsuite/modulefiles.4/loc_fdv2/2.0          |   2 +
 testsuite/modulefiles.4/loc_fdv2/2.1          |   2 +
 testsuite/modulefiles.4/loc_fdv2/2.2          |   2 +
 testsuite/modulefiles.4/loc_fdv2/2.3          |   2 +
 testsuite/modulefiles.4/loc_fdv3/1.0          |   3 +
 testsuite/modulefiles.4/loc_fdv3/1.5          |   3 +
 testsuite/modulefiles.4/loc_fdv3/2.0          |   3 +
 testsuite/modulefiles.4/loc_fdv4/1.0          |   2 +
 testsuite/modulefiles.4/loc_fdv4/1.1          |   2 +
 testsuite/modulefiles.4/loc_fdv4/2.0          |   2 +
 testsuite/modulefiles.4/loc_fdv5/.modulerc    |   3 +
 testsuite/modulefiles.4/loc_fdv5/1.0          |   2 +
 testsuite/modulefiles.4/loc_fdv5/2.0          |   2 +
 .../modules.20-locate/140-hide-full-path.exp  |   2 +
 .../modules.20-locate/170-fastdefvers.exp     | 244 ++++++++++++++++++
 .../modules.51-scan/030-scan_eval-avail.exp   |   6 +-
 .../modules.51-scan/033-scan_eval-spider.exp  |   6 +-
 49 files changed, 583 insertions(+), 24 deletions(-)
 create mode 100644 testsuite/mb/testenv_load3
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/.modulerc
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.1
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.2
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.3
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.4
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.5
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.6
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.7
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.8
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/1.9
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.1
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.2
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.3
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.4
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.5
 create mode 100644 testsuite/modulefiles.4/loc_fdv1/2.9
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/.version
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/1.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/1.1
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/1.2
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/1.3
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/1.4
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/1.5
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/2.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/2.1
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/2.2
 create mode 100644 testsuite/modulefiles.4/loc_fdv2/2.3
 create mode 100644 testsuite/modulefiles.4/loc_fdv3/1.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv3/1.5
 create mode 100644 testsuite/modulefiles.4/loc_fdv3/2.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv4/1.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv4/1.1
 create mode 100644 testsuite/modulefiles.4/loc_fdv4/2.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv5/.modulerc
 create mode 100644 testsuite/modulefiles.4/loc_fdv5/1.0
 create mode 100644 testsuite/modulefiles.4/loc_fdv5/2.0
 create mode 100644 testsuite/modules.20-locate/170-fastdefvers.exp

diff --git a/.hunspell.en.dic b/.hunspell.en.dic
index 1ffeab742..846a6d6c8 100644
--- a/.hunspell.en.dic
+++ b/.hunspell.en.dic
@@ -1312,6 +1312,9 @@ profiler
 moduleTop
 struct
 load2
+load3
+ms
+stopmod
 list2
 lrem
 replaceFromList
diff --git a/MIGRATING.rst b/MIGRATING.rst
index a737971fe..03d4489d4 100644
--- a/MIGRATING.rst
+++ b/MIGRATING.rst
@@ -38,21 +38,44 @@ have been implemented:
   match the module root name specification, instead of comparing against all
   loaded modules.
 
+* Lighter-weight resolution of an exact ``name/version`` specification: sites
+  with a modulepath directory holding hundreds or thousands of sibling
+  modulefiles reported slow ``module load`` commands even when the requested
+  version already exists. Correctly computing the implicit ``default`` and
+  ``latest`` symbolic versions of such a directory used to require validating
+  every sibling modulefile in it. The lookup now walks candidate versions from
+  the dictionary-highest to the dictionary-lowest and stops validating as soon
+  as this can be answered: either a higher valid version is found (the
+  requested one is then known not to be ``default`` or ``latest``), or the
+  requested version itself is reached, in which case
+  nothing higher exists. This bypasses the exhaustive scan without changing
+  the resolved result.
+
 For this work, the :command:`mb` utility was extended with new benchmark tests
-that loads 137 modulefiles, lists the loaded modules, and then purges them.
-Running this benchmark highlights the performance improvements, as shown in
-the table below:
+that loads 137 modulefiles (``load2``), lists the loaded modules (``list2``),
+and then purges them. Running this benchmark highlights the performance
+improvements, as shown in the table below:
 
 +---------+-------------+--------------------+
 |         |      v5.6.1 |             v5.7.0 |
 +=========+=============+====================+
-|    load |     1038 ms |      384 ms (-63%) |
+|   load2 |     1038 ms |      384 ms (-63%) |
 +---------+-------------+--------------------+
-|    list |      222 ms |       29 ms (-87%) |
+|   list2 |      222 ms |       29 ms (-87%) |
 +---------+-------------+--------------------+
 |   purge |      568 ms |      303 ms (-46%) |
 +---------+-------------+--------------------+
 
+A ``load3`` benchmark test was also added, loading a low, non-default
+version of a module out of 500 sibling versions in the same directory. It
+specifically exercises the lighter-weight resolution described above:
+
++---------+-------------+--------------------+
+|         |     v5.6.1  |             v5.7.0 |
++=========+=============+====================+
+|   load3 |       30 ms |       19 ms (-36%) |
++---------+-------------+--------------------+
+
 These measurements were obtained on a system where all modulefiles are stored
 on local flash storage. If your modulefiles reside on a shared network
 filesystem, using a `Module cache`_ is strongly recommended.
diff --git a/NEWS.rst b/NEWS.rst
index e9508bf06..c83cb2780 100644
--- a/NEWS.rst
+++ b/NEWS.rst
@@ -152,6 +152,13 @@ Modules 5.7.0 (not yet released)
   prepends and the entries it appends, so this entry is not silently
   absorbed by these commands' default de-duplication behavior nor relocated
   by the :mconfig:`path_entry_reorder` configuration option.
+* Resolve an exact ``name/version`` specification without validating every
+  sibling modulefile found in its directory, by walking versions from the
+  dictionary-highest to the dictionary-lowest and stopping as soon as the
+  implicit ``default`` and ``latest`` symbolic versions are settled. A
+  substantial performance improvement is observed when loading an existing
+  modulefile out of a directory holding hundreds or thousands of sibling
+  versions. (fix issue #561)
 
 
 .. _5.6 release notes:
diff --git a/script/mb b/script/mb
index 49bbdb579..f917e7741 100755
--- a/script/mb
+++ b/script/mb
@@ -1,7 +1,7 @@
 #!/usr/bin/env tclsh
 #
 # MB, make bench between modulecmd versions
-# Copyright (C) 2019-2025 Xavier Delaruelle
+# Copyright (C) 2019-2026 Xavier Delaruelle
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -27,7 +27,7 @@ Available tests:
   help, avail, avail_cache, avail2, avail2_cache, avail3, avail3_cache,
   avail4, avail4_cache, whatis, whatis_cache, whatis2, whatis2_cache,
   whatis3, whatis3_cache, apropos, load, load_cache, load2, load2_cache,
-  list, list2, purge, unload
+  load3, load3_cache, list, list2, purge, unload
   (all tests selected by default)
 
 Modes:
@@ -196,7 +196,8 @@ foreach arg $argv {
       help - avail - avail_cache - avail2 - avail2_cache - avail3 -\
          avail3_cache - avail4 - avail4_cache - whatis - whatis_cache -\
          whatis2 - whatis2_cache - whatis3 - whatis3_cache - apropos - load -\
-         load_cache - load2 - load2_cache - list - list2 - purge - unload {
+         load_cache - load2 - load2_cache - load3 - load3_cache -\
+         list - list2 - purge - unload {
          lappend testlist $arg
       }
       --with-lmod=* {
@@ -232,7 +233,7 @@ if {![info exists testlist]} {
       set testlist [list help avail avail_cache avail2 avail2_cache avail3\
          avail3_cache avail4 avail4_cache whatis whatis_cache whatis2\
          whatis2_cache whatis3 whatis3_cache apropos load load_cache load2\
-         load2_cache list list2 purge unload]
+         load2_cache load3 load3_cache list list2 purge unload]
    }
 } elseif {[info exists lmod_cmd]} {
    foreach test $testlist {
@@ -338,12 +339,70 @@ catch {unset env(__MODULES_SHARE_MODULEPATH)}
 # define bench tests and their arguments and environment
 set modpath $curdir/testsuite/modulefiles
 array set testsubcmdlist [list avail2 avail avail3 avail avail4 avail whatis2\
-   whatis whatis3 whatis load2 load list2 list]
+   whatis whatis3 whatis load2 load load3 load list2 list]
 array set testarglist [list avail2 load whatis2 load load load/all unload\
-   load/all load2 R-bundle-Bioconductor/3.18-foss-2023a-R-4.3.2]
+   load/all load2 R-bundle-Bioconductor/3.18-foss-2023a-R-4.3.2 load3\
+   bigmod/1.1]
 array set testoptlist [list avail4_lmod --ignore_cache load2_lmod\
    --ignore_cache]
 
+# the load3 bench needs a module root holding several hundred sibling
+# versions (mixing valid and invalid modulefiles, matching the shape
+# reported by sites with large modulepath directories), generated on the
+# fly rather than checked into the repository and removed once done
+set bigmoddir $modpath.bigmod/bigmod
+set need_bigmod [expr {{load3} in $testlist || {load3_cache} in $testlist}]
+if {$need_bigmod} {
+   file mkdir $bigmoddir
+   set bigmod_content {#%Module
+
+proc ModulesHelp {} {
+    puts stderr {Lorem ipsum dolor sit amet, consectetur adipiscing elit.}
+    puts stderr {Sed non risus. Suspendisse lectus tortor, dignissim sit amet,}
+    puts stderr {adipiscing nec, ultricies sed, dolor. Cras elementum ultrices diam.}
+    puts stderr {Maecenas ligula massa, varius a, semper congue, euismod non, mi.}
+    puts stderr {Proin porttitor, orci nec nonummy molestie, enim est eleifend mi,}
+    puts stderr {non fermentum diam nisl sit amet erat. Duis semper. Duis arcu massa,}
+    puts stderr {scelerisque vitae, consequat in, }
+    puts stderr {Lorem ipsum dolor sit amet, consectetur adipiscing elit.}
+    puts stderr {Sed non risus. Suspendisse lectus tortor, dignissim sit amet,}
+    puts stderr {adipiscing nec, ultricies sed, dolor. Cras elementum ultrices diam.}
+    puts stderr {Maecenas ligula massa, varius a, semper congue, euismod non, mi.}
+    puts stderr {Proin porttitor, orci nec nonummy molestie, enim est eleifend mi,}
+    puts stderr {non fermentum diam nisl sit amet erat. Duis semper. Duis arcu massa,}
+    puts stderr {scelerisque vitae, consequat in, }
+    puts stderr {Lorem ipsum dolor sit amet, consectetur adipiscing elit.}
+    puts stderr {Sed non risus. Suspendisse lectus tortor, dignissim sit amet,}
+    puts stderr {adipiscing nec, ultricies sed, dolor. Cras elementum ultrices diam.}
+    puts stderr {Maecenas ligula massa, varius a, semper congue, euismod non, mi.}
+    puts stderr {Proin porttitor, orci nec nonummy molestie, enim est eleifend mi,}
+    puts stderr {non fermentum diam nisl sit amet erat. Duis semper. Duis arcu massa,}
+    puts stderr {scelerisque vitae, consequat in, }
+}
+
+# comment code of the modulefile
+module-whatis {returns all various module-info values}
+
+# comment code of the modulefile
+setenv FOO value
+append-path BAR /path/to/directory
+setenv QUX {Lorem ipsum dolor sit amet, consectetur adipiscing elit.}
+setenv FOO2 value
+append-path BAR2 /path/to/directory
+setenv QUX2 {Lorem ipsum dolor sit amet, consectetur adipiscing elit.}
+}
+   for {set bigmodvers 1} {$bigmodvers <= 500} {incr bigmodvers} {
+      set fid [open $bigmoddir/1.$bigmodvers w]
+      puts $fid $bigmod_content
+      close $fid
+   }
+   foreach bigmodvers {50 150 250 350 450} {
+      set fid [open $bigmoddir/1.$bigmodvers.orig w]
+      puts $fid {not a modulefile}
+      close $fid
+   }
+}
+
 # load test environment recorded in external files
 foreach testenv_file [glob $curdir/testsuite/mb/testenv_*] {
    set test [string range [file tail $testenv_file] 8 end]
@@ -368,7 +427,8 @@ set testenvlist(purge_lmod) $testenvlist(list2_lmod)
 # some tests have a minimum version requirement
 array set testcompatlist [list avail3 4.6.0 whatis3 4.6.0 avail_cache 5.3.0\
    avail2_cache 5.3.0 avail3_cache 5.3.0 whatis_cache 5.3.0 whatis2_cache\
-   5.3.0 whatis3_cache 5.3.0 load_cache 5.3.0 load2_cache 5.3.0]
+   5.3.0 whatis3_cache 5.3.0 load_cache 5.3.0 load2_cache 5.3.0 load3_cache\
+   5.3.0]
 
 # adapt output table to test mode
 if {$mode eq {profile}} {
@@ -424,6 +484,11 @@ foreach tag $taglist {
       catch {file delete modulecmd.$tag lib/libtclenvmodules.so.$tag}
    }
 }
+
+# clean generated load3 bench modulefiles
+if {$need_bigmod} {
+   file delete -force $modpath.bigmod
+}
 catch {file delete tcl/mfinterp.tcl}
 
 # restore workspace if saved
diff --git a/tcl/modfind.tcl.in b/tcl/modfind.tcl.in
index 2311c3f64..30c921b7c 100644
--- a/tcl/modfind.tcl.in
+++ b/tcl/modfind.tcl.in
@@ -2984,10 +2984,112 @@ proc findModulesInMemCache {searchid} {
    return [list $match_searchid $mod_list]
 }
 
+# when 'mod_name' is 'stop_mod''s own parent directory, narrow
+# 'elt_list_name' (in the {path hid} pairs shape returned by
+# getFilesInDirectory) down to only what is needed to tell whether stop_mod
+# is the implicit 'default'/'latest' version of that directory: its
+# dotfiles (always kept, the general consolidation phase in getModules
+# deals with them normally) plus, among its plain elements, only the
+# dictionary range from stop_mod up to either the first higher element that
+# is itself valid and not hidden (stop_mod is then known not to be
+# default/latest) or the highest element if none qualifies. Left untouched
+# in any other case: this is not stop_mod's own directory, stop_mod does not
+# exist in it, or it is not itself a valid modulefile, in which case there
+# is nothing to optimize
+proc trimElemListForStopmod {dir mod_name stop_mod elt_list_name} {
+   if {![string length $stop_mod] || $mod_name ne [file dirname $stop_mod]} {
+      return
+   }
+
+   upvar $elt_list_name elt_list
+   array set elt_arr $elt_list
+
+   if {![info exists elt_arr($dir/$stop_mod)] || [lindex [checkValidModule\
+      $dir/$stop_mod] 0] ne {true}} {
+      return
+   }
+
+   # first fill updated element list with rc files if any and remove them from
+   # reference array to work only on other items
+   array set up_elt_arr {}
+   foreach rc_tail {.modulerc .version} {
+      set elt $dir/$mod_name/$rc_tail
+      if {[info exists elt_arr($elt)]} {
+         set up_elt_arr($elt) $elt_arr($elt)
+         unset elt_arr($elt)
+      }
+   }
+
+   set tail_list {}
+   foreach elt [array names elt_arr] {
+      lappend tail_list [file tail $elt]
+   }
+
+   # source the modulepath root '.modulerc' then this directory's own
+   # '.modulerc' and '.version' right away (in that order) if not already
+   # done, as any of them may set a hiding rule needed below, to correctly
+   # tell if a sibling actually is a qualifying higher element (guarded the
+   # same way the general consolidation phase guards its own later,
+   # deferred sourcing of them)
+   global g_rcfilesSourced
+   set top_rc_file $dir/.modulerc
+   if {![info exists g_rcfilesSourced($top_rc_file)] && [file readable\
+      $top_rc_file]} {
+      execute-modulerc $top_rc_file .modulerc .modulerc
+      set g_rcfilesSourced($top_rc_file) 1
+   }
+   foreach rc_tail {.modulerc .version} {
+      set rc_elt $dir/$mod_name/$rc_tail
+      if {[info exists up_elt_arr($rc_elt)] && ![info exists\
+         g_rcfilesSourced($rc_elt)]} {
+         set rc_mod $mod_name/$rc_tail
+         execute-modulerc $rc_elt $rc_mod $rc_mod
+         set g_rcfilesSourced($rc_elt) 1
+      }
+   }
+
+   # sort this directory's plain elements and look, starting from the
+   # highest one down to stop_mod, for the first element that is itself
+   # valid and not hidden: whether or not it turns out to be stop_mod
+   # itself, it is this directory's true implicit default/latest, needed
+   # as-is by the caller to correctly resolve it for every module in this
+   # directory, not just stop_mod. Only the elements from that point up to
+   # the highest one need to be kept to reflect it, plus stop_mod's own
+   # element if it lies below that point
+   set stop_tail [file tail $stop_mod]
+   set sorted_tails [lsort -dictionary $tail_list]
+   set stop_idx [lsearch -exact $sorted_tails $stop_tail]
+   set top_idx $stop_idx
+   for {set ti [expr {[llength $sorted_tails] - 1}]} {$ti > $stop_idx}\
+      {incr ti -1} {
+      set fp_tail [lindex $sorted_tails $ti]
+      set fp_elt $dir/$mod_name/$fp_tail
+      if {[file isdirectory $fp_elt]} {
+         # a nested version directory: its own validity cannot be settled
+         # without recursing into it, give up trying to stop early, keep
+         # everything untouched like usual
+         return
+      }
+      if {[lindex [checkValidModule $fp_elt] 0] eq {true} &&\
+         ![isModuleHidden $mod_name/$fp_tail $stop_mod 0 $fp_elt]} {
+         set top_idx $ti
+         break
+      }
+   }
+
+   # only keep rc files, stop_mod and highest element the updated structure
+   set up_elt_arr($dir/$stop_mod) $elt_arr($dir/$stop_mod)
+   if {$top_idx > $stop_idx} {
+      set elt $dir/$mod_name/[lindex $sorted_tails $top_idx]
+      set up_elt_arr($elt) $elt_arr($elt)
+   }
+   set elt_list [array get up_elt_arr]
+}
+
 # Walk through provided list of directories and files to find modules
 proc findModulesFromDirsAndFiles {dir full_list depthlvl fetch_mtime\
    res_arrname {indir_arrname {}} {hidden_listname {}} {fknown_arrname {}}\
-   {dknown_arrname {}}} {
+   {dknown_arrname {}} {stop_mod {}}} {
    # link to variables/arrays from upper context
    upvar $res_arrname mod_list
    if {$indir_arrname ne {}} {
@@ -3024,6 +3126,12 @@ proc findModulesFromDirsAndFiles {dir full_list depthlvl fetch_mtime\
                set mod_list($modulename) [list accesserr [parseAccessIssue\
                   $element] $element]
             } else {
+               # narrow elt_list down to what is needed to correctly tell
+               # whether stop_mod is the implicit default/latest version of
+               # this directory, when this is stop_mod's own directory
+               # (left untouched in any other case)
+               trimElemListForStopmod $dir $modulename $stop_mod elt_list
+
                # Add each element in the current directory to the list
                foreach {fpelt hid} $elt_list {
                   lappend full_list $fpelt
@@ -3082,13 +3190,15 @@ proc findModulesFromDirsAndFiles {dir full_list depthlvl fetch_mtime\
    }
 }
 
-# finds all module-related files matching mod in the module path dir
-proc findModules {dir mod depthlvl fetch_mtime} {
+# finds all module-related files matching mod in the module path dir.
+# 'stop_mod' helps optimize the search when looking for an exact existing
+# modulefile
+proc findModules {dir mod depthlvl fetch_mtime {stop_mod {}}} {
    reportDebug "finding '$mod' in $dir (depthlvl=$depthlvl,\
       fetch_mtime=$fetch_mtime)"
 
    # generated search id (for cache search/save) by compacting given args
-   set searchid $dir:$mod:$depthlvl:$fetch_mtime
+   set searchid $dir:$mod:$depthlvl:$fetch_mtime:$stop_mod
 
    # look at memory cache for a compatible result
    lassign [findModulesInMemCache $searchid] cache_searchid cache_list
@@ -3127,7 +3237,8 @@ proc findModules {dir mod depthlvl fetch_mtime} {
    }
 
    # walk through list of dirs and files to find modules
-   findModulesFromDirsAndFiles $dir $full_list $depthlvl $fetch_mtime mod_list
+   findModulesFromDirsAndFiles $dir $full_list $depthlvl $fetch_mtime\
+      mod_list {} {} {} {} $stop_mod
 
    reportDebug "found [array names mod_list]"
 
@@ -3212,6 +3323,18 @@ proc getModules {dir {mod {}} {fetch_mtime 0} {search {}} {filter {}}} {
       set add_rc_defs 1
       array set found_list {}
    } else {
+      # an exact 'name/version' query (no wildcard/contains, no result
+      # filtering), possibly along with a variant or an extra match search
+      # specifier, resolved in a single-module context (unlike a listing
+      # one, e.g. avail/whatis/search) lets findModules shortcut its
+      # directory search (see there); left empty in any other case
+      set stop_mod {}
+      set modnamevers [getModuleNameAndVersFromVersSpec $mod]
+      if {$resctx && $earlyfilter && $filter eq {} && [getCmpSpecFromVersSpec\
+         $mod] eq {eq} && $querydepth == 1} {
+         set stop_mod $modnamevers
+      }
+
       # find modules by searching mod root name in order to catch all module
       # related entries to correctly computed auto symbols afterward
 
@@ -3233,7 +3356,8 @@ proc getModules {dir {mod {}} {fetch_mtime 0} {search {}} {filter {}}} {
       # unless EMS need to be performed (findModules should fetch everything)
       set depthlvl [expr {$indepth || $ems_required ? 0 : $querydepth + 1}]
 
-      array set found_list [findModules $dir $findmod $depthlvl $fetch_mtime]
+      array set found_list [findModules $dir $findmod $depthlvl\
+         $fetch_mtime $stop_mod]
    }
 
    # Phase #1: consolidate every kind of entries (directory, modulefile,
diff --git a/testsuite/mb/testenv_load3 b/testsuite/mb/testenv_load3
new file mode 100644
index 000000000..6852f9c17
--- /dev/null
+++ b/testsuite/mb/testenv_load3
@@ -0,0 +1 @@
+MODULEPATH $modpath.bigmod
diff --git a/testsuite/modulefiles.4/.modulerc b/testsuite/modulefiles.4/.modulerc
index b51597ee2..bff9cf857 100644
--- a/testsuite/modulefiles.4/.modulerc
+++ b/testsuite/modulefiles.4/.modulerc
@@ -98,3 +98,11 @@ if {[info exists env(TESTSUITE_PROVIDE)]} {
         }
     }
 }
+
+if {[info exists env(TESTSUITE_FASTDEFVERS)]} {
+    switch -- $env(TESTSUITE_FASTDEFVERS) {
+        hide1 {
+            module-hide --hard loc_fdv4/2.0
+        }
+    }
+}
diff --git a/testsuite/modulefiles.4/loc_fdv1/.modulerc b/testsuite/modulefiles.4/loc_fdv1/.modulerc
new file mode 100644
index 000000000..5deac4da8
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/.modulerc
@@ -0,0 +1,3 @@
+#%Module
+
+module-hide --hard loc_fdv1/2.9
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.0 b/testsuite/modulefiles.4/loc_fdv1/1.0
new file mode 100644
index 000000000..f5b474723
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.0
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.1 b/testsuite/modulefiles.4/loc_fdv1/1.1
new file mode 100644
index 000000000..8ca1cf47e
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.1
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.1
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.2 b/testsuite/modulefiles.4/loc_fdv1/1.2
new file mode 100644
index 000000000..27229f05f
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.2
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.2
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.3 b/testsuite/modulefiles.4/loc_fdv1/1.3
new file mode 100644
index 000000000..a6120ecf3
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.3
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.3
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.4 b/testsuite/modulefiles.4/loc_fdv1/1.4
new file mode 100644
index 000000000..fe702f6bc
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.4
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.4
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.5 b/testsuite/modulefiles.4/loc_fdv1/1.5
new file mode 100644
index 000000000..916633b64
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.5
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.5
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.6 b/testsuite/modulefiles.4/loc_fdv1/1.6
new file mode 100644
index 000000000..ff7b5e132
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.6
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.6
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.7 b/testsuite/modulefiles.4/loc_fdv1/1.7
new file mode 100644
index 000000000..d6f0e3f93
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.7
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.7
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.8 b/testsuite/modulefiles.4/loc_fdv1/1.8
new file mode 100644
index 000000000..372a60278
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.8
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.8
diff --git a/testsuite/modulefiles.4/loc_fdv1/1.9 b/testsuite/modulefiles.4/loc_fdv1/1.9
new file mode 100644
index 000000000..a0885d6ab
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/1.9
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/1.9
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.0 b/testsuite/modulefiles.4/loc_fdv1/2.0
new file mode 100644
index 000000000..bf09db769
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.0
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.1 b/testsuite/modulefiles.4/loc_fdv1/2.1
new file mode 100644
index 000000000..cd7085264
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.1
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.1
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.2 b/testsuite/modulefiles.4/loc_fdv1/2.2
new file mode 100644
index 000000000..8b756faf7
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.2
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.2
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.3 b/testsuite/modulefiles.4/loc_fdv1/2.3
new file mode 100644
index 000000000..5c065a96c
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.3
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.3
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.4 b/testsuite/modulefiles.4/loc_fdv1/2.4
new file mode 100644
index 000000000..5660d3924
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.4
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.4
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.5 b/testsuite/modulefiles.4/loc_fdv1/2.5
new file mode 100644
index 000000000..930b987fb
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.5
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.5
diff --git a/testsuite/modulefiles.4/loc_fdv1/2.9 b/testsuite/modulefiles.4/loc_fdv1/2.9
new file mode 100644
index 000000000..80d339450
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv1/2.9
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv1/2.9
diff --git a/testsuite/modulefiles.4/loc_fdv2/.version b/testsuite/modulefiles.4/loc_fdv2/.version
new file mode 100644
index 000000000..f3f39e50f
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/.version
@@ -0,0 +1,3 @@
+#%Module
+
+module-version ./1.2 default
diff --git a/testsuite/modulefiles.4/loc_fdv2/1.0 b/testsuite/modulefiles.4/loc_fdv2/1.0
new file mode 100644
index 000000000..45f88a6d9
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/1.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/1.0
diff --git a/testsuite/modulefiles.4/loc_fdv2/1.1 b/testsuite/modulefiles.4/loc_fdv2/1.1
new file mode 100644
index 000000000..eaae4d117
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/1.1
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/1.1
diff --git a/testsuite/modulefiles.4/loc_fdv2/1.2 b/testsuite/modulefiles.4/loc_fdv2/1.2
new file mode 100644
index 000000000..712932b80
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/1.2
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/1.2
diff --git a/testsuite/modulefiles.4/loc_fdv2/1.3 b/testsuite/modulefiles.4/loc_fdv2/1.3
new file mode 100644
index 000000000..2b7f9e870
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/1.3
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/1.3
diff --git a/testsuite/modulefiles.4/loc_fdv2/1.4 b/testsuite/modulefiles.4/loc_fdv2/1.4
new file mode 100644
index 000000000..7e2938d98
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/1.4
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/1.4
diff --git a/testsuite/modulefiles.4/loc_fdv2/1.5 b/testsuite/modulefiles.4/loc_fdv2/1.5
new file mode 100644
index 000000000..44c5c86ee
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/1.5
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/1.5
diff --git a/testsuite/modulefiles.4/loc_fdv2/2.0 b/testsuite/modulefiles.4/loc_fdv2/2.0
new file mode 100644
index 000000000..d9a78461a
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/2.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/2.0
diff --git a/testsuite/modulefiles.4/loc_fdv2/2.1 b/testsuite/modulefiles.4/loc_fdv2/2.1
new file mode 100644
index 000000000..5fb061da4
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/2.1
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/2.1
diff --git a/testsuite/modulefiles.4/loc_fdv2/2.2 b/testsuite/modulefiles.4/loc_fdv2/2.2
new file mode 100644
index 000000000..3e3c824ee
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/2.2
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/2.2
diff --git a/testsuite/modulefiles.4/loc_fdv2/2.3 b/testsuite/modulefiles.4/loc_fdv2/2.3
new file mode 100644
index 000000000..bd0ae6fc7
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv2/2.3
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv2/2.3
diff --git a/testsuite/modulefiles.4/loc_fdv3/1.0 b/testsuite/modulefiles.4/loc_fdv3/1.0
new file mode 100644
index 000000000..7cf37a395
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv3/1.0
@@ -0,0 +1,3 @@
+#%Module
+variant myvar val1 val2
+module-whatis loc_fdv3/1.0
diff --git a/testsuite/modulefiles.4/loc_fdv3/1.5 b/testsuite/modulefiles.4/loc_fdv3/1.5
new file mode 100644
index 000000000..ca1d578cb
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv3/1.5
@@ -0,0 +1,3 @@
+#%Module
+variant myvar val1 val2
+module-whatis loc_fdv3/1.5
diff --git a/testsuite/modulefiles.4/loc_fdv3/2.0 b/testsuite/modulefiles.4/loc_fdv3/2.0
new file mode 100644
index 000000000..a7ad333cf
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv3/2.0
@@ -0,0 +1,3 @@
+#%Module
+variant myvar val1 val2
+module-whatis loc_fdv3/2.0
diff --git a/testsuite/modulefiles.4/loc_fdv4/1.0 b/testsuite/modulefiles.4/loc_fdv4/1.0
new file mode 100644
index 000000000..f291eb664
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv4/1.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv4/1.0
diff --git a/testsuite/modulefiles.4/loc_fdv4/1.1 b/testsuite/modulefiles.4/loc_fdv4/1.1
new file mode 100644
index 000000000..37e2ebba8
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv4/1.1
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv4/1.1
diff --git a/testsuite/modulefiles.4/loc_fdv4/2.0 b/testsuite/modulefiles.4/loc_fdv4/2.0
new file mode 100644
index 000000000..6d0cd1618
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv4/2.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv4/2.0
diff --git a/testsuite/modulefiles.4/loc_fdv5/.modulerc b/testsuite/modulefiles.4/loc_fdv5/.modulerc
new file mode 100644
index 000000000..71f10e209
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv5/.modulerc
@@ -0,0 +1,3 @@
+#%Module
+
+module-hide --hard [file dirname $ModulesCurrentModulefile]/2.0
diff --git a/testsuite/modulefiles.4/loc_fdv5/1.0 b/testsuite/modulefiles.4/loc_fdv5/1.0
new file mode 100644
index 000000000..e478e5df0
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv5/1.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv5/1.0
diff --git a/testsuite/modulefiles.4/loc_fdv5/2.0 b/testsuite/modulefiles.4/loc_fdv5/2.0
new file mode 100644
index 000000000..cf1329052
--- /dev/null
+++ b/testsuite/modulefiles.4/loc_fdv5/2.0
@@ -0,0 +1,2 @@
+#%Module
+module-whatis loc_fdv5/2.0
diff --git a/testsuite/modules.20-locate/140-hide-full-path.exp b/testsuite/modules.20-locate/140-hide-full-path.exp
index 17c063ab9..9d2f2bc14 100644
--- a/testsuite/modules.20-locate/140-hide-full-path.exp
+++ b/testsuite/modules.20-locate/140-hide-full-path.exp
@@ -131,6 +131,7 @@ set tserr "$modlin Aliases $modlin
 tag/1.1.al -> tag/1.0
 
 $modlin Versions $modlin
+loc_fdv2/default -> loc_fdv2/1.2
 tag/1.1.sym -> tag/1.0"
 
 testouterr_cmd_re sh {aliases} OK $tserr
@@ -167,6 +168,7 @@ set tserr "$modlin Aliases $modlin
 tag/1.1.al -> tag/1.0
 
 $modlin Versions $modlin
+loc_fdv2/default -> loc_fdv2/1.2
 tag/1.1.sym -> tag/1.0"
 
 testouterr_cmd_re sh {aliases} OK $tserr
diff --git a/testsuite/modules.20-locate/170-fastdefvers.exp b/testsuite/modules.20-locate/170-fastdefvers.exp
new file mode 100644
index 000000000..79bf456c8
--- /dev/null
+++ b/testsuite/modules.20-locate/170-fastdefvers.exp
@@ -0,0 +1,244 @@
+##############################################################################
+#   Modules Revision 3.0
+#   Providing a flexible user environment
+#
+#   File:		modules.20-locate/%M%
+#   Revision:		%I%
+#   First Edition:	2026/07/26
+#   Last Mod.:		%U%, %G%
+#
+#   Authors:		Xavier Delaruelle, xavier.delaruelle@cea.fr
+#
+#   Description:	Testuite testsequence
+#   Command:		load, display
+#   Modulefiles:	loc_fdv1, loc_fdv2, loc_fdv3, loc_fdv4, loc_fdv5
+#   Sub-Command:
+#
+#   Comment:	%C{
+#			Check that the lighter-weight resolution attempted for an exact
+#			'name/version' specification that matches an existing modulefile
+#			(see findModulesFromDirsAndFiles's 'stopmod' handling) resolves
+#			the implicit 'default' and 'latest' symbolic versions exactly
+#			like the exhaustive search does, on a directory holding many
+#			sibling versions: a hard hidden modulefile sorting above the
+#			actual highest usable version, an explicitly defined 'default'
+#			distinct from the implicit 'latest', a variant value specified
+#			along with the query, a hiding rule set in the modulepath's own
+#			top-level '.modulerc' and a hiding rule targeting a full path
+#			modulefile designation.
+#		}C%
+#
+##############################################################################
+
+#
+# Variables for this test
+#
+
+# use a dedicated modulepath so these new fixtures do not affect other tests
+# that enumerate the whole content of the default modulepath
+setenv_path_var MODULEPATH $modpath.4
+
+set module_1 "loc_fdv1"
+set module_1_low "$module_1/1.0"
+set module_1_top "$module_1/2.5"
+set module_1_hidden "$module_1/2.9"
+set modulefile_1_low "$modpath.4/$module_1_low"
+set modulefilere_1_low "$modpathre.4/$module_1_low"
+set modulefile_1_top "$modpath.4/$module_1_top"
+set modulefilere_1_top "$modpathre.4/$module_1_top"
+
+set module_2 "loc_fdv2"
+set module_2_default "$module_2/1.2"
+set module_2_top "$module_2/2.3"
+set modulefile_2_default "$modpath.4/$module_2_default"
+set modulefilere_2_default "$modpathre.4/$module_2_default"
+set modulefile_2_top "$modpath.4/$module_2_top"
+set modulefilere_2_top "$modpathre.4/$module_2_top"
+
+set module_3 "loc_fdv3"
+set module_3_low "$module_3/1.0"
+set module_3_top "$module_3/2.0"
+set modulefile_3_low "$modpath.4/$module_3_low"
+set modulefile_3_top "$modpath.4/$module_3_top"
+
+set module_4 "loc_fdv4"
+set module_4_low "$module_4/1.0"
+set module_4_top "$module_4/1.1"
+set module_4_hidden "$module_4/2.0"
+set modulefile_4_low "$modpath.4/$module_4_low"
+set modulefile_4_top "$modpath.4/$module_4_top"
+
+set module_5 "loc_fdv5"
+set module_5_top "$module_5/1.0"
+set module_5_hidden "$module_5/2.0"
+set modulefile_5_top "$modpath.4/$module_5_top"
+
+#
+# loc_fdv1: bare name and low exact version both resolve correctly, skipping
+# past an invalid modulefile (3.0) and a hard hidden one (2.9), neither of
+# which should be considered a candidate for the implicit highest version
+#
+
+set ans [list]
+if {[is_conf_enabled advversspec implicitdefault]} {
+    lappend ans [list set __MODULES_LMALTNAME\
+        $module_1_top&as|$module_1/default&as|$module_1/latest]
+}
+lappend ans [list set _LMFILES_ $modulefile_1_top]
+lappend ans [list set LOADEDMODULES $module_1_top]
+
+test_cmd "sh" "load $module_1" [if_implicitdefault $ans ERR]\
+    [if_implicitdefault 0 1]
+
+testouterr_cmd_re "sh" "display $module_1" [if_implicitdefault OK ERR]\
+    [if_implicitdefault "$modlin\n$modulefilere_1_top:\n\nmodule-whatis\\s+$module_1_top\n$modlin"\
+    "$err_nodefault'$module_1'"]
+
+#
+# loading the low exact version directly must succeed and must not carry the
+# 'default' or 'latest' alternate names, as a higher usable version exists
+#
+
+set ans [list]
+lappend ans [list set _LMFILES_ $modulefile_1_low]
+lappend ans [list set LOADEDMODULES $module_1_low]
+
+test_cmd "sh" "load $module_1_low" $ans
+
+testouterr_cmd_re "sh" "display $module_1_low" "OK"\
+    "$modlin\n$modulefilere_1_low:\n\nmodule-whatis\\s+$module_1_low\n$modlin"
+
+#
+# loading the actual highest usable version directly must carry both the
+# 'default' and 'latest' alternate names
+#
+
+set ans [list]
+if {[is_conf_enabled advversspec implicitdefault]} {
+    lappend ans [list set __MODULES_LMALTNAME\
+        $module_1_top&as|$module_1/default&as|$module_1/latest]
+}
+lappend ans [list set _LMFILES_ $modulefile_1_top]
+lappend ans [list set LOADEDMODULES $module_1_top]
+
+test_cmd "sh" "load $module_1_top" $ans
+
+#
+# the hard hidden version stays unreachable even when queried by its exact
+# name
+#
+
+testouterr_cmd_re "sh" "display $module_1_hidden" "ERR"\
+    "$err_path'$module_1_hidden'"
+
+skip_if_quick_mode
+
+#
+# loc_fdv2: an explicitly defined 'default' distinct from the implicit
+# 'latest' must each resolve independently and carry only their own
+# alternate name, not the other one. Unlike loc_fdv1's implicit default,
+# this one is set via a '.version' rule, so it resolves regardless of the
+# 'implicit_default' configuration option
+#
+
+set ans [list]
+lappend ans [list set __MODULES_LMALTNAME\
+    $module_2_default&$module_2/default&$module_2]
+lappend ans [list set _LMFILES_ $modulefile_2_default]
+lappend ans [list set LOADEDMODULES $module_2_default]
+
+test_cmd "sh" "load $module_2" $ans
+
+testouterr_cmd_re "sh" "display $module_2" "OK"\
+    "$modlin\n$modulefilere_2_default:\n\nmodule-whatis\\s+$module_2_default\n$modlin"
+
+set ans [list]
+if {[is_conf_enabled advversspec implicitdefault]} {
+    lappend ans [list set __MODULES_LMALTNAME\
+        $module_2_top&as|$module_2/latest]
+}
+lappend ans [list set _LMFILES_ $modulefile_2_top]
+lappend ans [list set LOADEDMODULES $module_2_top]
+
+test_cmd "sh" "load $module_2_top" $ans
+
+#
+# loc_fdv3: a variant value specified along with an exact 'name/version'
+# query must not prevent the fast path from being taken, nor affect its
+# correctness
+#
+
+if {[is_conf_enabled advversspec]} {
+
+set ans [list]
+lappend ans [list set __MODULES_LMVARIANT $module_3_low&myvar|val2|0|0]
+lappend ans [list set _LMFILES_ $modulefile_3_low]
+lappend ans [list set LOADEDMODULES $module_3_low]
+
+test_cmd "sh" "load $module_3_low myvar=val2" $ans
+
+set ans [list]
+lappend ans [list set __MODULES_LMVARIANT $module_3_top&myvar|val2|0|0]
+if {[is_conf_enabled advversspec implicitdefault]} {
+    lappend ans [list set __MODULES_LMALTNAME\
+        $module_3_top&as|$module_3/default&as|$module_3/latest]
+}
+lappend ans [list set _LMFILES_ $modulefile_3_top]
+lappend ans [list set LOADEDMODULES $module_3_top]
+
+test_cmd "sh" "load $module_3_top myvar=val2" $ans
+
+}
+
+#
+# loc_fdv4: a module-hide rule declared in the modulepath's own top-level
+# '.modulerc' (as opposed to the module directory's own '.modulerc', already
+# covered by loc_fdv1) must also be honored while resolving the implicit
+# highest version
+#
+
+setenv_var TESTSUITE_FASTDEFVERS hide1
+
+set ans [list]
+lappend ans [list set _LMFILES_ $modulefile_4_low]
+lappend ans [list set LOADEDMODULES $module_4_low]
+
+test_cmd "sh" "load $module_4_low" $ans
+
+set ans [list]
+if {[is_conf_enabled advversspec implicitdefault]} {
+    lappend ans [list set __MODULES_LMALTNAME\
+        $module_4_top&as|$module_4/default&as|$module_4/latest]
+}
+lappend ans [list set _LMFILES_ $modulefile_4_top]
+lappend ans [list set LOADEDMODULES $module_4_top]
+
+test_cmd "sh" "load $module_4_top" $ans
+
+testouterr_cmd_re "sh" "display $module_4_hidden" "ERR"\
+    "$err_path'$module_4_hidden'"
+
+#
+# loc_fdv5: a module-hide rule targeting a full path modulefile designation
+# (as opposed to a relative 'name/version' one) must also be honored while
+# resolving the implicit highest version
+#
+
+set ans [list]
+if {[is_conf_enabled advversspec implicitdefault]} {
+    lappend ans [list set __MODULES_LMALTNAME\
+        $module_5_top&as|$module_5/default&as|$module_5/latest]
+}
+lappend ans [list set _LMFILES_ $modulefile_5_top]
+lappend ans [list set LOADEDMODULES $module_5_top]
+
+test_cmd "sh" "load $module_5_top" $ans
+
+testouterr_cmd_re "sh" "display $module_5_hidden" "ERR"\
+    "$err_path'$module_5_hidden'"
+
+#
+# Cleanup
+#
+
+reset_test_env
diff --git a/testsuite/modules.51-scan/030-scan_eval-avail.exp b/testsuite/modules.51-scan/030-scan_eval-avail.exp
index 65b992ae8..5398f3f88 100644
--- a/testsuite/modules.51-scan/030-scan_eval-avail.exp
+++ b/testsuite/modules.51-scan/030-scan_eval-avail.exp
@@ -257,7 +257,7 @@ testouterr_cmd_re sh {avail -T -t scan@1.1:2.1 foo=val4} OK $tserr
 set tserr ".*
 Get modules: {} matching 'scan@1.1:2.0 foo=val2' in ''
 .*
-Get modules: {scan/2.0 scan/1.1} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
+Get modules: {scan/(2\.0|1\.1) scan/(2\.0|1\.1)} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
 scan/1.1{foo=val1,val2,val3}
 scan/2.0{foo=val2,val3,val4}"
 testouterr_cmd_re sh {avail -T -t scan@1.1:2.0 foo=val2} OK $tserr
@@ -332,7 +332,7 @@ testouterr_cmd_re sh {avail -T -t scan@1.1:2.0 foo=val4} OK $tserr
 set tserr ".*
 Get modules: {} matching 'scan@1.1:2.1 foo=val2' in ''
 .*
-Get modules: {scan/2.0 scan/1.1 scan/2.1} matching 'scan@1.1:2.1 foo=val2' in '$mpre'
+Get modules: {scan/(2\.0|1\.1|2\.1) scan/(2\.0|1\.1|2\.1) scan/(2\.0|1\.1|2\.1)} matching 'scan@1.1:2.1 foo=val2' in '$mpre'
 scan/1.1{foo=val1,val2,val3}
 scan/2.0{foo=val2,val3,val4}
 scan/2.1{foo=val2,val3,val4}"
@@ -358,7 +358,7 @@ testouterr_cmd_re sh {avail -T -t scan@latest foo=val4} OK $tserr
 set tserr ".*
 Get modules: {} matching 'scan@1.1:2.0 foo=val2' in ''
 .*
-Get modules: {scan/2.0 scan/1.1} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
+Get modules: {scan/(2\.0|1\.1) scan/(2\.0|1\.1)} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
 scan/1.1{foo=val1,val2,val3}
 scan/2.0{foo=val2,val3,val4}"
 testouterr_cmd_re sh {avail -T -t scan@1.1:2.0 foo=val2} OK $tserr
diff --git a/testsuite/modules.51-scan/033-scan_eval-spider.exp b/testsuite/modules.51-scan/033-scan_eval-spider.exp
index 8eee908ae..71bf9075f 100644
--- a/testsuite/modules.51-scan/033-scan_eval-spider.exp
+++ b/testsuite/modules.51-scan/033-scan_eval-spider.exp
@@ -261,7 +261,7 @@ testouterr_cmd_re sh {spider -T -t scan@1.1:2.1 foo=val4} OK $tserr
 set tserr ".*
 Get modules: {} matching 'scan@1.1:2.0 foo=val2' in ''
 .*
-Get modules: {scan/2.0 scan/1.1} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
+Get modules: {scan/(2\.0|1\.1) scan/(2\.0|1\.1)} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
 scan/1.1{foo=val1,val2,val3}
 scan/2.0{foo=val2,val3,val4}"
 testouterr_cmd_re sh {spider -T -t scan@1.1:2.0 foo=val2} OK $tserr
@@ -336,7 +336,7 @@ testouterr_cmd_re sh {spider -T -t scan@1.1:2.0 foo=val4} OK $tserr
 set tserr ".*
 Get modules: {} matching 'scan@1.1:2.1 foo=val2' in ''
 .*
-Get modules: {scan/2.0 scan/1.1 scan/2.1} matching 'scan@1.1:2.1 foo=val2' in '$mpre'
+Get modules: {scan/(2\.1|2\.0|1\.1) scan/(2\.1|2\.0|1\.1) scan/(2\.1|2\.0|1\.1)} matching 'scan@1.1:2.1 foo=val2' in '$mpre'
 scan/1.1{foo=val1,val2,val3}
 scan/2.0{foo=val2,val3,val4}
 scan/2.1{foo=val2,val3,val4}"
@@ -362,7 +362,7 @@ testouterr_cmd_re sh {spider -T -t scan@latest foo=val4} OK $tserr
 set tserr ".*
 Get modules: {} matching 'scan@1.1:2.0 foo=val2' in ''
 .*
-Get modules: {scan/2.0 scan/1.1} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
+Get modules: {scan/(2\.0|1\.1) scan/(2\.0|1\.1)} matching 'scan@1.1:2.0 foo=val2' in '$mpre'
 scan/1.1{foo=val1,val2,val3}
 scan/2.0{foo=val2,val3,val4}"
 testouterr_cmd_re sh {spider -T -t scan@1.1:2.0 foo=val2} OK $tserr