Define stricter naming rules for variants

Instead of just requiring that first character of variant name should
correspond to the [A-Za-z0-9_] range, now variant names should only be
made of [A-Za-z0-9_-] characters. First character of these names cannot
be "-" and full name cannot be a number.

Adapt module specification parsing not to consider string parts
beginning with boolean variant prefix "+" and "~" as a variant
specification if the string after the prefix does not corresponds to a
valid variant name.

With this change, "/path/to/modul+files/foo/1.0" and "java/17.0.2+8" are
now parsed as only a module name and version rather also including a
boolean variant specification.

Fixes #527

tcl/mfcmd.tcl

@@ -1901,6 +1901,11 @@ proc source-sh-di {args} {
    }
 }
 
+proc isVariantNameValid {name} {
+   return [expr {![string is digit -strict $name] && [regexp\
+      {^[A-Za-z0-9_][A-Za-z0-9_-]*$} $name]}]
+}
+
 # parse arguments set on a variant modulefile command
 proc parseVariantCommandArgs {args} {
    set dflvalue {}
@@ -1944,7 +1949,7 @@ proc parseVariantCommandArgs {args} {
    if {![info exists name]} {
       knerror {No variant name specified}
    }
-   if {![string match {[A-Za-z0-9_]} [string index $name 0]]} {
+   if {![isVariantNameValid $name]} {
       knerror "Invalid variant name '$name'"
    }
    set values [lrange $args $i end]

tcl/modspec.tcl

@@ -1324,38 +1324,32 @@ proc parseModuleSpecificationProcAdvVersSpec {mlspec nonamespec xtspec\
       if {[regexp {^[a-z-]+:} $arg]} {
          lappend curarglist $arg
       } else {
+         set split_chars {@ ~ +}
+         lappend split_chars {*}[array names ::g_shortcutVariant]
+         set split_arg_list {}
          set previ 0
          for {set i 1} {$i < [string length $arg]} {incr i} {
-            set c [string index $arg $i]
-            switch -- $c {
-               @ - ~ {
-                  lappend curarglist [string range $arg $previ $i-1]
-                  set previ $i
-               }
-               + {
-                  # allow one or more '+' char at end of module name if not
-                  # followed by non-special character (@, ~ or /)
-                  set nexti [expr {$i + 1}]
-                  if {$nexti < [string length $arg]} {
-                     switch -- [string index $arg $nexti] {
-                        @ - + - ~ - / {}
-                        default {
-                           lappend curarglist [string range $arg $previ $i-1]
-                           set previ $i
-                        }
-                     }
-                  }
-               }
-               default {
-                  # check if a variant shortcut matches
-                  if {[info exists ::g_shortcutVariant($c)]} {
-                     lappend curarglist [string range $arg $previ $i-1]
-                     set previ $i
-                  }
-               }
+            if {[string index $arg $i] in $split_chars} {
+               lappend split_arg_list [string range $arg $previ $i-1]
+               set previ $i
+            }
+         }
+         lappend split_arg_list [string range $arg $previ $i-1]
+
+         # unsplit some arg parts: those starting with boolean variant prefix
+         # (+ or ~) but not followed by a valid variant name
+         set prev_arg [lindex $split_arg_list 0]
+         for {set i 1} {$i < [llength $split_arg_list]} {incr i} {
+            set split_arg [lindex $split_arg_list $i]
+            if {[string index $split_arg 0] ni {+ ~} || [isVariantNameValid\
+               [string range $split_arg 1 end]]} {
+               lappend curarglist $prev_arg
+               set prev_arg $split_arg
+            } else {
+               append prev_arg $split_arg
             }
          }
-         lappend curarglist [string range $arg $previ $i-1]
+         lappend curarglist $prev_arg
       }
 
       # parse each specification element