Reduce false positives for @hsh{$s} and @ary[$s] warnings

This resolves tickets #28380 and #114024.

Commit 95a31aad5 did something similar to this for the new %hash{...}
syntax.  This commit extends it to @ slices and combines the two
code paths.

The heuristics in toke.c can easily produce false positives.  So the
op is flagged as being a candidate for the warning.  Then when op.c
has the op tree available, it examines it to see whether the heuristic
may have been a false positive.

This avoids bugs with qw "foo bar baz" and sub calls triggering
the warning.

The source code is no longer available for the warning, so we recon-
struct it from the op tree, skipping the subscript if it is anything
other than a const op.

This means that @hash{$foo} comes out as @hash{...} and @hash{foo} as
@hash{"foo"}.  It also meeans that @hash{"]"} is displayed correctly
instead of as @hash{"].

Commit 95a31aad5 also modified the heuristic for %hash{...} to exempt
qw altogether.  But it did not exempt it if it was preceded by a tab.
So this commit rectifies that.

This commit also improves the false positive detection by exempting
any ops returning lists that can get past toke.c’s heuristic.  I went
through the entire list of ops, but I may have missed some.

Also, @ slices on the lhs of = are exempt, as they change the context
and are hence actually useful.

1 files changed, 1 insertions, 1 deletions

diff --git a/op.h b/op.h
index f491e2e275..3978acdfa4 100644
--- a/op.h
+++ b/op.h
@@ -221,7 +221,7 @@ Deprecated.  Use C<GIMME_V> instead.
 #define OPpEARLY_CV		32	/* foo() called before sub foo was parsed */
   /* OP_?ELEM only */
 #define OPpLVAL_DEFER		16	/* Defer creation of array/hash elem */
-  /* OP_RV2[AH]V OP_KV[AH]SLICE */
+  /* OP_RV2[AH]V OP_KV[AH]SLICE OP_[AH]SLICE */
 #define OPpSLICEWARNING		4	/* warn about %hash{$scalar} */
   /* OP_RV2[SAH]V, OP_GVSV, OP_ENTERITER only */
 #define OPpOUR_INTRO		16	/* Variable was in an our() */