This is my attempt to implement P0614R1, a C++20 feature whereby we may now use
an init-statement in a range-based for loop like this:
for (int i = bar (); const auto &x : a)
// ...
The somewhat tricky part was to distinguish a range-based for from an ordinary
for
statement, hence the cp_parser_range_based_for_with_init_p shenanigans. Note
that we must be able to cope with lambdas/statement-expressions in the
initializer as well as with loops such as
for (int i = 0; int j = 0; )
// ...
and the following seems to handle all of it.
What d'ya think?
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2018-05-21 Marek Polacek <pola...@redhat.com>
Implement P0614R1, Range-based for statements with initializer.
* parser.c (cp_parser_range_based_for_with_init_p): New.
(cp_parser_init_statement): Use it. Parse the optional init-statement
for a range-based for loop.
* g++.dg/cpp2a/range-for1.C: New test.
* g++.dg/cpp2a/range-for2.C: New test.
* g++.dg/cpp2a/range-for3.C: New test.
* g++.dg/cpp2a/range-for4.C: New test.
* g++.dg/cpp2a/range-for5.C: New test.
* g++.dg/cpp2a/range-for6.C: New test.
diff --git gcc/cp/parser.c gcc/cp/parser.c
index c0058085ee9..47a825f2da0 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -11255,6 +11255,39 @@ cp_parser_statement_seq_opt (cp_parser* parser, tree
in_statement_expr)
}
}
+/* Return true if this is the C++20 version of range-based-for with
+ init-statement. */
+
+static bool
+cp_parser_range_based_for_with_init_p (cp_parser *parser)
+{
+ bool r = false;
+
+ /* Save tokens so that we can put them back. */
+ cp_lexer_save_tokens (parser->lexer);
+
+ /* There has to be an unnested ; followed by an unnested :. */
+ if (cp_parser_skip_to_closing_parenthesis_1 (parser,
+ /*recovering=*/false,
+ CPP_SEMICOLON,
+ /*consume_paren=*/false) != -1)
+ goto out;
+
+ /* We found the semicolon, eat it now. */
+ cp_lexer_consume_token (parser->lexer);
+ /* Now look for ':' that is not nested in () or {}. */
+ r = (cp_parser_skip_to_closing_parenthesis_1 (parser,
+ /*recovering=*/false,
+ CPP_COLON,
+ /*consume_paren=*/false) == -1);
+
+out:
+ /* Roll back the tokens we skipped. */
+ cp_lexer_rollback_tokens (parser->lexer);
+
+ return r;
+}
+
/* Return true if we're looking at (init; cond), false otherwise. */
static bool
@@ -12242,7 +12275,7 @@ cp_parser_iteration_statement (cp_parser* parser, bool
*if_p, bool ivdep,
simple-declaration */
static bool
-cp_parser_init_statement (cp_parser* parser, tree *decl)
+cp_parser_init_statement (cp_parser *parser, tree *decl)
{
/* If the next token is a `;', then we have an empty
expression-statement. Grammatically, this is also a
@@ -12255,6 +12288,29 @@ cp_parser_init_statement (cp_parser* parser, tree
*decl)
bool is_range_for = false;
bool saved_colon_corrects_to_scope_p = parser->colon_corrects_to_scope_p;
+ /* Try to parse the init-statement. */
+ if (cp_parser_range_based_for_with_init_p (parser))
+ {
+ tree dummy;
+ cp_parser_parse_tentatively (parser);
+ /* Parse the declaration. */
+ cp_parser_simple_declaration (parser,
+ /*function_definition_allowed_p=*/false,
+ &dummy);
+ cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
+ if (!cp_parser_parse_definitely (parser))
+ /* That didn't work, try to parse it as an expression-statement. */
+ cp_parser_expression_statement (parser, NULL_TREE);
+
+ if (cxx_dialect < cxx2a)
+ {
+ pedwarn (cp_lexer_peek_token (parser->lexer)->location, 0,
+ "range-based %<for%> loops with initializer only "
+ "available with -std=c++2a or -std=gnu++2a");
+ *decl = error_mark_node;
+ }
+ }
+
/* A colon is used in range-based for. */
parser->colon_corrects_to_scope_p = false;
@@ -12268,7 +12324,7 @@ cp_parser_init_statement (cp_parser* parser, tree *decl)
parser->colon_corrects_to_scope_p = saved_colon_corrects_to_scope_p;
if (cp_lexer_next_token_is (parser->lexer, CPP_COLON))
{
- /* It is a range-for, consume the ':' */
+ /* It is a range-for, consume the ':'. */
cp_lexer_consume_token (parser->lexer);
is_range_for = true;
if (cxx_dialect < cxx11)
@@ -12280,9 +12336,9 @@ cp_parser_init_statement (cp_parser* parser, tree *decl)
}
}
else
- /* The ';' is not consumed yet because we told
- cp_parser_simple_declaration not to. */
- cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
+ /* The ';' is not consumed yet because we told
+ cp_parser_simple_declaration not to. */
+ cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
if (cp_parser_parse_definitely (parser))
return is_range_for;
diff --git gcc/testsuite/g++.dg/cpp2a/range-for1.C
gcc/testsuite/g++.dg/cpp2a/range-for1.C
index e69de29bb2d..3a5523585a1 100644
--- gcc/testsuite/g++.dg/cpp2a/range-for1.C
+++ gcc/testsuite/g++.dg/cpp2a/range-for1.C
@@ -0,0 +1,16 @@
+// P0614R1
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+void
+fn1 ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+
+ for (int i = 0; auto x : a) // { dg-warning "range-based .for. loops with
initializer only available with" "" { target c++17_down } }
+ ++i;
+
+ int i;
+ for (i = 0; auto x : a) // { dg-warning "range-based .for. loops with
initializer only available with" "" { target c++17_down } }
+ ++i;
+}
diff --git gcc/testsuite/g++.dg/cpp2a/range-for2.C
gcc/testsuite/g++.dg/cpp2a/range-for2.C
index e69de29bb2d..acb16c57d1c 100644
--- gcc/testsuite/g++.dg/cpp2a/range-for2.C
+++ gcc/testsuite/g++.dg/cpp2a/range-for2.C
@@ -0,0 +1,16 @@
+// P0614R1
+// { dg-do compile }
+// { dg-options "-std=c++2a" }
+
+void
+fn1 ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+
+ for (int i = 0; auto x : a)
+ ++i;
+
+ int i;
+ for (i = 0; auto x : a)
+ ++i;
+}
diff --git gcc/testsuite/g++.dg/cpp2a/range-for3.C
gcc/testsuite/g++.dg/cpp2a/range-for3.C
index e69de29bb2d..291e605b92f 100644
--- gcc/testsuite/g++.dg/cpp2a/range-for3.C
+++ gcc/testsuite/g++.dg/cpp2a/range-for3.C
@@ -0,0 +1,26 @@
+// P0614R1
+// { dg-do compile }
+// { dg-options "-std=c++2a" }
+
+static const int a[] = { 1, 2, 3, 4, 5 };
+extern void foo (int);
+extern void bar (int, int);
+
+constexpr int
+baz ()
+{
+ return 6;
+}
+
+void
+fn1 (int i)
+{
+ for ((i += 2); auto x : a)
+ foo (i);
+
+ for (auto j = 0, k = 0; auto x : a)
+ bar (j + k, x);
+
+ for (constexpr int j = baz (); auto x : a)
+ bar (x, j);
+}
diff --git gcc/testsuite/g++.dg/cpp2a/range-for4.C
gcc/testsuite/g++.dg/cpp2a/range-for4.C
index e69de29bb2d..6ba783f46cb 100644
--- gcc/testsuite/g++.dg/cpp2a/range-for4.C
+++ gcc/testsuite/g++.dg/cpp2a/range-for4.C
@@ -0,0 +1,27 @@
+// P0614R1
+// { dg-do run }
+// { dg-options "-std=c++2a" }
+
+int
+main ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+
+ for (int i = 1; auto x : a)
+ if (i++ != x)
+ __builtin_abort ();
+
+ int i;
+ for (i = 1; auto x : a)
+ if (i++ != x)
+ __builtin_abort ();
+
+ i = 0;
+ for (i++; auto x : a)
+ if (i != 1)
+ __builtin_abort ();
+
+ for (int s[] = { 1, 1, 1 }; auto x : s)
+ if (x != 1)
+ __builtin_abort ();
+}
diff --git gcc/testsuite/g++.dg/cpp2a/range-for5.C
gcc/testsuite/g++.dg/cpp2a/range-for5.C
index e69de29bb2d..62f1c2f04e1 100644
--- gcc/testsuite/g++.dg/cpp2a/range-for5.C
+++ gcc/testsuite/g++.dg/cpp2a/range-for5.C
@@ -0,0 +1,46 @@
+// P0614R1
+// { dg-do compile }
+// { dg-options "-std=c++2a" }
+
+void
+fn1 ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+
+ for (int i = 0; auto x : a)
+ ++i;
+
+ i = 0; // { dg-error "not declared" }
+
+ for (int i = 0; auto x : a)
+ {
+ for (int j = 0; auto x : a)
+ {
+ for (int k = 0; auto x : a)
+ k++;
+ k++; // { dg-error "not declared" }
+ }
+ j++; // { dg-error "not declared" }
+ }
+}
+
+void
+fn2 ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+ for (int i = 0; auto x : a)
+ int i = 3; // { dg-error "redeclaration" }
+}
+void
+fn3 ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+
+ for (;:) // { dg-error "expected" }
+ {
+ }
+
+ for (;;:) // { dg-error "expected" }
+ {
+ }
+}
diff --git gcc/testsuite/g++.dg/cpp2a/range-for6.C
gcc/testsuite/g++.dg/cpp2a/range-for6.C
index e69de29bb2d..4cee60a839e 100644
--- gcc/testsuite/g++.dg/cpp2a/range-for6.C
+++ gcc/testsuite/g++.dg/cpp2a/range-for6.C
@@ -0,0 +1,17 @@
+// P0614R1
+// { dg-do run }
+// { dg-options "-std=c++2a" }
+
+int
+main ()
+{
+ int a[] = { 1, 2, 3, 4, 5 };
+
+ for (int i = []{ return 3; }(); auto x : a)
+ if (i != 3)
+ __builtin_abort ();
+
+ for (int i = ({ 3; }); auto x : a)
+ if (i != 3)
+ __builtin_abort ();
+}
