Forbid braces as format delimiters

As long the argument line is not missing, braces can be used
for a format:

# valid
format foo {
@<<<
$a
}

but if the argument line is missing, you get a syntax error:

# invalid
format foo {
@<<<
}

and also if the name is missing:

# invalid
format {
@<<<
$a
}

If you use = then you can use a closing brace to terminate the format,
but only if the argument line is missing:

# valid, but useless
format =
@<<<
}

# invalid
format =
@<<<
$a
}

In commit 79072805 (perl 5.0 alpha 20), the lexer was changed to lie
to the parser about formats’ = and . delimiters, pretending they are
actually { and }, because the bracket-handling code takes care of all
the scoping issues (well, most of them).

Unfortunately, this implementation detail can leak through, but it is
far from consistent, as shown above.

Fixing this makes it easier to fix other bugs.

We do this by recording the fact that we are dealing with a format
token before jumping to the bracket code.  And we feed format-specific
tokens to the parser in that case, so it can’t get fake brackets and
real brackets mixed up.

1 files changed, 16 insertions, 1 deletions

diff --git a/t/op/write.t b/t/op/write.t
index a648902fb5..17b8869eb5 100644
--- a/t/op/write.t
+++ b/t/op/write.t
@@ -61,7 +61,7 @@ for my $tref ( @NumTests ){
 my $bas_tests = 20;
 
 # number of tests in section 3
-my $bug_tests = 8 + 3 * 3 * 5 * 2 * 3 + 2 + 66 + 4 + 2 + 3 + 96 + 2;
+my $bug_tests = 8 + 3 * 3 * 5 * 2 * 3 + 2 + 66 + 4 + 2 + 3 + 96 + 4;
 
 # number of tests in section 4
 my $hmb_tests = 35;
@@ -1002,6 +1002,21 @@ write UNDEF;
 pass "freeing current handle in format";
 undef $^A;
 
+ok !eval q|
+format foo {
+@<<<
+$a
+}
+;1
+|, 'format foo { ... } is not allowed';
+
+ok !eval q|
+format =
+@<<<
+}
+;1
+|, 'format = ... } is not allowed';
+
 
 #############################
 ## Section 4