Test, doc, implement #!include_default as memory-only, not changing disk file

Changes

@@ -1,6 +1,7 @@
 Revision history for ExtUtils-Manifest
 
 {{$NEXT}}
+  - #!include_default now memory-only, not changing MANIFEST.SKIP file.
 
 1.73  2021-01-16
   - Calculate absolute path to MANIFEST.SKIP (in $DEFAULT_MSKIP) at module

lib/ExtUtils/Manifest.pm

@@ -404,6 +404,20 @@ a given filename should be skipped.
 
 =cut
 
+sub _process_skipline {
+    local $_ = shift;
+    chomp;
+    s/\r//;
+    $_ =~ qr{^\s*(?:(?:'([^\\']*(?:\\.[^\\']*)*)')|([^#\s]\S*))?(?:(?:\s*)|(?:\s+(.*?)\s*))$};
+    #my $comment = $3;
+    my $filename = $2;
+    if ( defined($1) ) {
+      $filename = $1;
+      $filename =~ s/\\(['\\])/$1/g;
+    }
+    $filename;
+}
+
 # returns an anonymous sub that decides if an argument matches
 sub maniskip {
     my @skip ;
@@ -412,16 +426,14 @@ sub maniskip {
     local(*M, $_);
     open M, "< $mfile" or open M, "< $DEFAULT_MSKIP" or return sub {0};
     while (<M>){
-        chomp;
-        s/\r//;
-        $_ =~ qr{^\s*(?:(?:'([^\\']*(?:\\.[^\\']*)*)')|([^#\s]\S*))?(?:(?:\s*)|(?:\s+(.*?)\s*))$};
-        #my $comment = $3;
-        my $filename = $2;
-        if ( defined($1) ) {
-          $filename = $1;
-          $filename =~ s/\\(['\\])/$1/g;
+        if (/^#!include_default\s*$/) {
+            if (my @default = _include_mskip_file()) {
+                warn "Debug: Including default MANIFEST.SKIP\n" if $Debug;
+                push @skip, grep $_, map _process_skipline($_), @default;
+            }
+            next;
         }
-        next if (not defined($filename) or not $filename);
+        next unless my $filename = _process_skipline($_);
         push @skip, _macify($filename);
     }
     close M;
@@ -452,14 +464,6 @@ sub _check_mskip_directives {
         return;
     }
     while (<M>) {
-        if (/^#!include_default\s*$/) {
-            if (my @default = _include_mskip_file()) {
-                push @lines, @default;
-                warn "Debug: Including default MANIFEST.SKIP\n" if $Debug;
-                $flag++;
-            }
-            next;
-        }
         if (/^#!include\s+(.*)\s*$/) {
             my $external_file = $1;
             if (my @external = _include_mskip_file($external_file)) {
@@ -809,11 +813,17 @@ files. At present two such directives are recognized.
 
 =item #!include_default
 
-This inserts the contents of the default MANIFEST.SKIP file
+This tells ExtUtils::Manifest to read the default F<MANIFEST.SKIP>
+file and skip files accordingly, but I<not> to include it in the local
+F<MANIFEST.SKIP>. This is intended to skip files according to a system
+default, which can change over time without requiring further changes
+to the distribution's F<MANIFEST.SKIP>.
 
 =item #!include /Path/to/another/manifest.skip
 
-This inserts the contents of the specified external file
+This inserts the contents of the specified external file in the local
+F<MANIFEST.SKIP>. This is intended for authors to have a central
+F<MANIFEST.SKIP> file, and to include it with their various distributions.
 
 =back
 

t/Manifest.t

@@ -13,7 +13,7 @@ BEGIN {
 }
 chdir 't';
 
-use Test::More tests => 98;
+use Test::More tests => 99;
 use Cwd;
 
 use File::Spec;
@@ -438,6 +438,13 @@ my @funky_keys = qw(space space_quote space_backslash space_quote_backslash);
 
     my $extsep = $Is_VMS_noefs ? '_' : '.';
     $Files{"$_.bak"}++ for ('MANIFEST', "MANIFEST${extsep}SKIP");
+
+    my $mskip_contents = do {
+        local $/;
+        open my $fh, '<', "MANIFEST${extsep}SKIP" or return;
+        <$fh>;
+    };
+    unlike $mskip_contents, qr{^\Q^my\E}m, 'include_default memory-only';
 }
 
 add_file('MANIFEST'   => 'Makefile.PL');