no bareword_filehandes: don't look up class barewords as handles

This prevents SomeBareword from being looked up as a filehandle:

  no feature "bareword_filehandles";
  SomeBareword->method();

Since "bareword_filehandles" is explicitly about bareword handles,
it does not prevent other string to object/class look ups from
resolving the class as a filehandle, eg for the following:

  "SomeLiteral"->method();
  my $x = "SomeVariable";
  $x->method();

both are looked up as file handles per normal.

Note that in any of these cases, with or without the
bareword_filehandles feature, if the name is a bareword that
has been resolved as a class name since the last time the
stash cache was cleared, it will be resolved as a class name,
not a filehandle.

Fixes #19426

embed.fnc

@@ -4577,6 +4577,8 @@ S |void |inplace_aassign|NN OP *o
 RST |bool |is_handle_constructor \
  |NN const OP *o \
  |I32 numargs
+Ti |bool |is_standard_filehandle_name \
+ |NN const char *fhname
 S |OP * |listkids |NULLOK OP *o
 S |bool |looks_like_bool|NN const OP *o
 S |OP * |modkids |NULLOK OP *o \

embed.h

@@ -1378,6 +1378,7 @@
 # define gen_constant_list(a) S_gen_constant_list(aTHX_ a)
 # define inplace_aassign(a) S_inplace_aassign(aTHX_ a)
 # define is_handle_constructor S_is_handle_constructor
+# define is_standard_filehandle_name S_is_standard_filehandle_name
 # define listkids(a) S_listkids(aTHX_ a)
 # define looks_like_bool(a) S_looks_like_bool(aTHX_ a)
 # define modkids(a,b) S_modkids(aTHX_ a,b)

op.c

@@ -712,17 +712,27 @@ Perl_no_bareword_allowed(pTHX_ OP *o)
  o->op_private &= ~OPpCONST_STRICT; /* prevent warning twice about the same OP */
 }
 
+/*
+Return true if the supplied string is the name of one of the built-in
+filehandles.
+*/
+
+PERL_STATIC_INLINE bool
+S_is_standard_filehandle_name(const char *fhname) {
+ return strEQ(fhname, "STDERR")
+ || strEQ(fhname, "STDOUT")
+ || strEQ(fhname, "STDIN")
+ || strEQ(fhname, "_")
+ || strEQ(fhname, "ARGV")
+ || strEQ(fhname, "ARGVOUT")
+ || strEQ(fhname, "DATA");
+}
+
 void
 Perl_no_bareword_filehandle(pTHX_ const char *fhname) {
  PERL_ARGS_ASSERT_NO_BAREWORD_FILEHANDLE;
 
- if (strNE(fhname, "STDERR")
- && strNE(fhname, "STDOUT")
- && strNE(fhname, "STDIN")
- && strNE(fhname, "_")
- && strNE(fhname, "ARGV")
- && strNE(fhname, "ARGVOUT")
- && strNE(fhname, "DATA")) {
+ if (!is_standard_filehandle_name(fhname)) {
  qerror(Perl_mess(aTHX_ "Bareword filehandle \"%s\" not allowed under 'no feature \"bareword_filehandles\"'", fhname));
  }
 }
@@ -14601,6 +14611,7 @@ Perl_ck_subr(pTHX_ OP *o)
  CV *cv;
  GV *namegv;
  SV **const_class = NULL;
+ OP *const_op = NULL;
 
  PERL_ARGS_ASSERT_CK_SUBR;
 
@@ -14630,12 +14641,14 @@ Perl_ck_subr(pTHX_ OP *o)
  if (aop->op_type == OP_CONST) {
  aop->op_private &= ~OPpCONST_STRICT;
  const_class = &cSVOPx(aop)->op_sv;
+ const_op = aop;
  }
  else if (aop->op_type == OP_LIST) {
  OP * const sib = OpSIBLING(cUNOPx(aop)->op_first);
  if (sib && sib->op_type == OP_CONST) {
  sib->op_private &= ~OPpCONST_STRICT;
  const_class = &cSVOPx(sib)->op_sv;
+ const_op = sib;
  }
  }
  /* make class name a shared cow string to speedup method calls */
@@ -14644,6 +14657,12 @@ Perl_ck_subr(pTHX_ OP *o)
  STRLEN len;
  const char* str = SvPV(*const_class, len);
  if (len) {
+ if (!FEATURE_BAREWORD_FILEHANDLES_IS_ENABLED
+ && !is_standard_filehandle_name(str)
+ && (const_op->op_private & OPpCONST_BARE)) {
+ cvop->op_private |= OPpMETH_NO_BAREWORD_IO;
+ }
+
  SV* const shared = newSVpvn_share(
  str, SvUTF8(*const_class)
  ? -(SSize_t)len : (SSize_t)len,