From 3ce45d2161eb6dde6fbb82adde7d421df1d2b5f9 Mon Sep 17 00:00:00 2001
From: "Paul \"LeoNerd\" Evans" <leonerd@leonerd.org.uk>
Date: Wed, 17 Jan 2024 18:02:00 +0000
Subject: [PATCH] `use VERSION` implies `use builtin :VERSION`

---
 op.c             | 10 ++++++++++
 pod/perlfunc.pod | 18 ++++++++++++------
 t/comp/use.t     | 14 +++++++++++++-
 3 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/op.c b/op.c
index 9029126ea5930..5a37ae2fcbe22 100644
--- a/op.c
+++ b/op.c
@@ -8046,6 +8046,16 @@ Perl_utilize(pTHX_ int aver, I32 floor, OP *version, OP *idop, OP *arg)
                 PL_hints &= ~HINT_STRICT_VARS;
         }
 
+        /* As an optimisation, there's no point scanning for changes of
+         * visible builtin functions when switching between versions earlier
+         * than v5.39, when any became visible at all
+         */
+        if ((shortver >= SHORTVER(5, 39)) || (PL_prevailing_version >= SHORTVER(5, 39))) {
+            prepare_export_lexical();
+            import_builtin_bundle(shortver, true);
+            finish_export_lexical();
+        }
+
         PL_prevailing_version = shortver;
     }
 
diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 3364c1fd5eb62..bb2106b3f27ee 100644
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -10161,12 +10161,18 @@ Compare with L<C<require>|/require VERSION>, which can do a similar check
 at run time.
 
 If the specified Perl version is 5.12 or higher, strictures are enabled
-lexically as with L<C<use strict>|strict>.  Similarly, if the specified
-Perl version is 5.35.0 or higher, L<warnings> are enabled.  Later use of
-C<use VERSION> will override all behavior of a previous C<use VERSION>,
-possibly removing the C<strict>, C<warnings>, and C<feature> added by it.
-C<use VERSION> does not load the F<feature.pm>, F<strict.pm>, or
-F<warnings.pm> files.
+lexically as with L<C<use strict>|strict>.
+
+If the specified Perl version is 5.35.0 or higher, L<warnings> are enabled.
+
+If the specified Perl version is 5.39.0 or higher, builtin functions are
+imported lexically as with L<C<use builtin>|builtin> with a corresponding
+version bundle.
+
+Later use of C<use VERSION> will override all behavior of a previous
+C<use VERSION>, possibly removing the C<strict>, C<warnings>, C<feature> and
+C<builtin> effects added by it.  C<use VERSION> does not load the
+F<feature.pm>, F<strict.pm>, F<warnings.pm> or F<builtin.pm> files.
 
 In the current implementation, any explicit use of C<use strict> or
 C<no strict> overrides C<use VERSION>, even if it comes before it.
diff --git a/t/comp/use.t b/t/comp/use.t
index 8111b6941f5c4..e6042f16aef6e 100644
--- a/t/comp/use.t
+++ b/t/comp/use.t
@@ -6,7 +6,7 @@ BEGIN {
     $INC{"feature.pm"} = 1; # so we don't attempt to load feature.pm
 }
 
-print "1..85\n";
+print "1..88\n";
 
 # Can't require test.pl, as we're testing the use/require mechanism here.
 
@@ -170,6 +170,18 @@ ok $@, 'no strict vars allows ver decl to enable refs';
 eval 'no strict "vars"; use 5.012; ursine_word';
 ok $@, 'no strict vars allows ver decl to enable subs';
 
+# check that "use 5.39.0" and higher imports builtins
+{
+    my $result;
+
+    $result = eval 'use 5.39.0; my $t = true; $t eq "1"';
+    is ($@, "", 'builtin funcs available after use 5.39.0');
+    ok ($result, 'imported true is eq "1"');
+
+    eval 'use 5.39.0; use 5.36.0; my $t = true;';
+    like ($@, qr/^Bareword "true" not allowed while "strict subs" in use at /,
+        'builtin funcs are removed by use 5.36.0');
+}
 
 { use test_use }	# check that subparse saves pending tokens