This patch implements P1161R3, Deprecate uses of the comma operator in
subscripting expressions:
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1161r3.html>
which made its way to C++20. New [depr.comma.subscript] shows:
void f(int *a, int b, int c) {
a[b,c]; // deprecated
a[(b,c)]; // OK
}
I've added a new option, -Wcomma-subscript, so that this warning can be
selectively turned off in c++2a, where it is enabled by default, and turned
on in lower standards, to check if your codebase has any occurrences of it,
without needing to change the -std=.
As for implementation, I've extended cp_parser_skip_to_closing_square_bracket_1
so that we can check for a non-nested token inside [ ].
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-08-03 Marek Polacek <pola...@redhat.com>
PR c++/91338 - Implement P1161R3: Deprecate a[b,c].
* c-opts.c (c_common_post_options): Enable -Wcomma-subscript by
default for C++2a.
* c.opt (Wcomma-subscript): New warning.
* parser.c (cp_parser_postfix_open_square_expression): Warn about uses
of a comma operator within a subscripting expression.
(cp_parser_skip_to_closing_square_bracket_1): New function, made out
of...
(cp_parser_skip_to_closing_square_bracket): ...this.
* doc/invoke.texi: Document -Wcomma-subscript.
* g++.dg/cpp2a/comma1.C: New test.
* g++.dg/cpp2a/comma2.C: New test.
* g++.dg/cpp2a/comma3.C: New test.
diff --git gcc/c-family/c-opts.c gcc/c-family/c-opts.c
index e97bbdf5c6f..e43172598f3 100644
--- gcc/c-family/c-opts.c
+++ gcc/c-family/c-opts.c
@@ -916,6 +916,10 @@ c_common_post_options (const char **pfilename)
if (!global_options_set.x_warn_register)
warn_register = cxx_dialect >= cxx17;
+ /* -Wcomma-subscript is enabled by default in C++20. */
+ if (!global_options_set.x_warn_comma_subscript)
+ warn_comma_subscript = cxx_dialect >= cxx2a;
+
/* Declone C++ 'structors if -Os. */
if (flag_declone_ctor_dtor == -1)
flag_declone_ctor_dtor = optimize_size;
diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index 4c8b0026000..257cadfa5f1 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -428,6 +428,10 @@ Wclobbered
C ObjC C++ ObjC++ Var(warn_clobbered) Warning EnabledBy(Wextra)
Warn about variables that might be changed by \"longjmp\" or \"vfork\".
+Wcomma-subscript
+C++ ObjC++ Var(warn_comma_subscript) Warning
+Warn about uses of a comma operator within a subscripting expression.
+
Wcomment
C ObjC C++ ObjC++ CPP(warn_comments) CppReason(CPP_W_COMMENTS)
Var(cpp_warn_comment) Init(0) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
Warn about possibly nested block comments, and C++ comments spanning more than
one physical line.
diff --git gcc/cp/parser.c gcc/cp/parser.c
index ebeffdb775f..1a5ae147b84 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -2669,6 +2669,8 @@ static bool cp_parser_init_statement_p
(cp_parser *);
static bool cp_parser_skip_to_closing_square_bracket
(cp_parser *);
+static int cp_parser_skip_to_closing_square_bracket_1
+ (cp_parser *, enum cpp_ttype);
/* Concept-related syntactic transformations */
@@ -7522,7 +7524,33 @@ cp_parser_postfix_open_square_expression (cp_parser
*parser,
index = cp_parser_braced_list (parser, &expr_nonconst_p);
}
else
- index = cp_parser_expression (parser);
+ {
+ /* [depr.comma.subscript]: A comma expression appearing as
+ the expr-or-braced-init-list of a subscripting expression
+ is deprecated. A parenthesized comma expression is not
+ deprecated. */
+ if (warn_comma_subscript)
+ {
+ /* Save tokens so that we can put them back. */
+ cp_lexer_save_tokens (parser->lexer);
+
+ /* Look for ',' that is not nested in () or {}. */
+ if (cp_parser_skip_to_closing_square_bracket_1 (parser,
+ CPP_COMMA) == -1)
+ {
+ auto_diagnostic_group d;
+ warning_at (cp_lexer_peek_token (parser->lexer)->location,
+ OPT_Wcomma_subscript,
+ "top-level comma expression in array subscript "
+ "is deprecated");
+ }
+
+ /* Roll back the tokens we skipped. */
+ cp_lexer_rollback_tokens (parser->lexer);
+ }
+
+ index = cp_parser_expression (parser);
+ }
}
parser->greater_than_is_operator_p = saved_greater_than_is_operator_p;
@@ -22857,16 +22885,25 @@ cp_parser_braced_list (cp_parser* parser, bool*
non_constant_p)
}
/* Consume tokens up to, and including, the next non-nested closing `]'.
- Returns true iff we found a closing `]'. */
+ Returns 1 iff we found a closing `]'. Returns -1 if OR_TTYPE is not
+ CPP_EOF and we found an unnested token of that type. */
-static bool
-cp_parser_skip_to_closing_square_bracket (cp_parser *parser)
+static int
+cp_parser_skip_to_closing_square_bracket_1 (cp_parser *parser,
+ enum cpp_ttype or_ttype)
{
unsigned square_depth = 0;
+ unsigned paren_depth = 0;
+ unsigned brace_depth = 0;
while (true)
{
- cp_token * token = cp_lexer_peek_token (parser->lexer);
+ cp_token *token = cp_lexer_peek_token (parser->lexer);
+
+ /* Have we found what we're looking for before the closing square? */
+ if (token->type == or_ttype && or_ttype != CPP_EOF
+ && brace_depth == 0 && paren_depth == 0 && square_depth == 0)
+ return -1;
switch (token->type)
{
@@ -22876,20 +22913,38 @@ cp_parser_skip_to_closing_square_bracket (cp_parser
*parser)
/* FALLTHRU */
case CPP_EOF:
/* If we've run out of tokens, then there is no closing `]'. */
- return false;
+ return 0;
case CPP_OPEN_SQUARE:
++square_depth;
break;
case CPP_CLOSE_SQUARE:
- if (!square_depth--)
+ if (square_depth-- == 0)
{
cp_lexer_consume_token (parser->lexer);
- return true;
+ return 1;
}
break;
+ case CPP_OPEN_BRACE:
+ ++brace_depth;
+ break;
+
+ case CPP_CLOSE_BRACE:
+ if (brace_depth-- == 0)
+ return 0;
+ break;
+
+ case CPP_OPEN_PAREN:
+ ++paren_depth;
+ break;
+
+ case CPP_CLOSE_PAREN:
+ if (paren_depth-- == 0)
+ return 0;
+ break;
+
default:
break;
}
@@ -22899,6 +22954,15 @@ cp_parser_skip_to_closing_square_bracket (cp_parser
*parser)
}
}
+/* Consume tokens up to, and including, the next non-nested closing `]'.
+ Returns true iff we found a closing `]'. */
+
+static bool
+cp_parser_skip_to_closing_square_bracket (cp_parser *parser)
+{
+ return cp_parser_skip_to_closing_square_bracket_1 (parser, CPP_EOF) == 1;
+}
+
/* Return true if we are looking at an array-designator, false otherwise. */
static bool
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index 7b3c77b8033..01aab60f895 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -230,7 +230,8 @@ in the following sections.
-fvisibility-inlines-hidden @gol
-fvisibility-ms-compat @gol
-fext-numeric-literals @gol
--Wabi=@var{n} -Wabi-tag -Wconversion-null -Wctor-dtor-privacy @gol
+-Wabi=@var{n} -Wabi-tag -Wcomma-subscript -Wconversion-null @gol
+-Wctor-dtor-privacy @gol
-Wdelete-non-virtual-dtor -Wdeprecated-copy -Wdeprecated-copy-dtor @gol
-Wliteral-suffix @gol
-Wmultiple-inheritance -Wno-init-list-lifetime @gol
@@ -3037,6 +3038,24 @@ Warn when a type with an ABI tag is used in a context
that does not
have that ABI tag. See @ref{C++ Attributes} for more information
about ABI tags.
+@item -Wcomma-subscript @r{(C++ and Objective-C++ only)}
+@opindex Wcomma-subscript
+@opindex Wno-comma-subscript
+Warn about uses of a comma expression within a subscripting expression.
+This usage was deprecated in C++2a. However, a comma expression wrapped
+in @code{( )} is not deprecated. Example:
+
+@smallexample
+@group
+void f(int *a, int b, int c) @{
+ a[b,c]; // deprecated
+ a[(b,c)]; // OK
+@}
+@end group
+@end smallexample
+
+Enabled by default with @option{-std=c++2a}.
+
@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
@opindex Wctor-dtor-privacy
@opindex Wno-ctor-dtor-privacy
diff --git gcc/testsuite/g++.dg/cpp2a/comma1.C
gcc/testsuite/g++.dg/cpp2a/comma1.C
new file mode 100644
index 00000000000..5de48b4cdb9
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/comma1.C
@@ -0,0 +1,26 @@
+// PR c++/91338 - P1161R3: Deprecate a[b,c].
+// { dg-do compile { target c++11 } }
+
+struct S {
+ int operator,(int) { return 42; }
+};
+
+void
+fn (int *a, int b, int c)
+{
+ a[b,c]; // { dg-warning "top-level comma expression in array subscript is
deprecated" "" { target c++2a } }
+ a[(b,c)];
+
+ a[(void) b, c]; // { dg-warning "top-level comma expression in array
subscript is deprecated" "" { target c++2a } }
+ a[((void) b, c)];
+
+ a[(void) b, (void) c, (void) b, b]; // { dg-warning "top-level comma
expression in array subscript is deprecated" "" { target c++2a } }
+ a[((void) b, (void) c, (void) b, b)];
+
+ a[S(), 10]; // { dg-warning "top-level comma expression in array subscript
is deprecated" "" { target c++2a } }
+ a[(S(), 10)];
+
+ a[int{(1,2)}];
+ a[int{(1,2)}, int{}]; // { dg-warning "top-level comma expression in array
subscript is deprecated" "" { target c++2a } }
+ a[(int{(1,2)}, int{})];
+}
diff --git gcc/testsuite/g++.dg/cpp2a/comma2.C
gcc/testsuite/g++.dg/cpp2a/comma2.C
new file mode 100644
index 00000000000..383079ce4f8
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/comma2.C
@@ -0,0 +1,27 @@
+// PR c++/91338 - P1161R3: Deprecate a[b,c].
+// { dg-do compile { target c++2a } }
+// { dg-options "-Wno-comma-subscript" }
+
+struct S {
+ int operator,(int) { return 42; }
+};
+
+void
+fn (int *a, int b, int c)
+{
+ a[b,c]; // { dg-bogus "top-level comma expression in array subscript is
deprecated" }
+ a[(b,c)];
+
+ a[(void) b, c]; // { dg-bogus "top-level comma expression in array subscript
is deprecated" }
+ a[((void) b, c)];
+
+ a[(void) b, (void) c, (void) b, b]; // { dg-bogus "top-level comma
expression in array subscript is deprecated" }
+ a[((void) b, (void) c, (void) b, b)];
+
+ a[S(), 10]; // { dg-bogus "top-level comma expression in array subscript is
deprecated" }
+ a[(S(), 10)];
+
+ a[int{(1,2)}];
+ a[int{(1,2)}, int{}]; // { dg-bogus "top-level comma expression in array
subscript is deprecated" }
+ a[(int{(1,2)}, int{})];
+}
diff --git gcc/testsuite/g++.dg/cpp2a/comma3.C
gcc/testsuite/g++.dg/cpp2a/comma3.C
new file mode 100644
index 00000000000..59a518382d7
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/comma3.C
@@ -0,0 +1,27 @@
+// PR c++/91338 - P1161R3: Deprecate a[b,c].
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wcomma-subscript" }
+
+struct S {
+ int operator,(int) { return 42; }
+};
+
+void
+fn (int *a, int b, int c)
+{
+ a[b,c]; // { dg-warning "top-level comma expression in array subscript is
deprecated" }
+ a[(b,c)];
+
+ a[(void) b, c]; // { dg-warning "top-level comma expression in array
subscript is deprecated" }
+ a[((void) b, c)];
+
+ a[(void) b, (void) c, (void) b, b]; // { dg-warning "top-level comma
expression in array subscript is deprecated" }
+ a[((void) b, (void) c, (void) b, b)];
+
+ a[S(), 10]; // { dg-warning "top-level comma expression in array subscript
is deprecated" }
+ a[(S(), 10)];
+
+ a[int{(1,2)}];
+ a[int{(1,2)}, int{}]; // { dg-warning "top-level comma expression in array
subscript is deprecated" }
+ a[(int{(1,2)}, int{})];
+}
