On Wed, 2017-10-11 at 15:51 -0400, Jason Merrill wrote:
> On Tue, Sep 26, 2017 at 3:27 PM, David Malcolm <dmalc...@redhat.com>
> wrote:
> > * cp-tree.h (struct saved_scope): Add "location" field.
>
> saved_scope seems like the wrong place for this; it's only
> interesting
> at parse time, so having it saved during template instantiation
> doesn't seem useful. I'd prefer to put it in cp_parser and have
> maybe_show_extern_c_location look in the_parser.
>
> Jason
Here's an updated version that moves it there.
Other changes in v2:
- handle nested linkage specifications
- put the note on the string-literal, rather than the extern:
note: 'extern "C"' linkage started here
extern "C" {
^~~
Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
OK for trunk?
Thanks
Dave
Blurb from v1:
If the user fails to close an extern "C" linkage specifier, and then
uses templates, they will run into "template with C linkage" errors.
>From personal experience, it can be hard to tell where the
extern "C" began. As of r251026 there will be a message highlighting
the unclosed '{', but this may be hard to spot at the very end of
the errors.
This patch adds a note to the various diagnostics that complain
about C linkage, showing the user where the extern "C" specification
began.
gcc/cp/ChangeLog:
* cp-tree.h (maybe_show_extern_c_location): New decl.
* decl.c (grokfndecl): When complaining about literal operators
with C linkage, issue a note giving the location of the
extern "C".
* parser.c (cp_parser_new): Initialize new field
"innermost_linkage_specification_location".
(cp_parser_linkage_specification): Store the location
of the string-literal token within the cp_parser.
(cp_parser_explicit_specialization): When complaining about
template specializations with C linkage, issue a note giving the
location of the extern "C".
(cp_parser_explicit_template_declaration): Likewise for templates.
(maybe_show_extern_c_location): New function.
* parser.h (struct cp_parser): New field
"innermost_linkage_specification_location".
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/udlit-extern-c.C: New test case.
* g++.dg/diagnostic/unclosed-extern-c.C: Add example of a template
erroneously covered by an unclosed extern "C".
* g++.dg/template/extern-c.C: New test case.
---
gcc/cp/cp-tree.h | 1 +
gcc/cp/decl.c | 1 +
gcc/cp/parser.c | 29 ++++++++++
gcc/cp/parser.h | 4 ++
gcc/testsuite/g++.dg/cpp0x/udlit-extern-c.C | 7 +++
.../g++.dg/diagnostic/unclosed-extern-c.C | 11 +++-
gcc/testsuite/g++.dg/template/extern-c.C | 66 ++++++++++++++++++++++
7 files changed, 118 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/udlit-extern-c.C
create mode 100644 gcc/testsuite/g++.dg/template/extern-c.C
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 82ebc28..df3d198 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -6362,6 +6362,7 @@ extern bool parsing_nsdmi (void);
extern bool parsing_default_capturing_generic_lambda_in_template (void);
extern void inject_this_parameter (tree, cp_cv_quals);
extern location_t defarg_location (tree);
+extern void maybe_show_extern_c_location (void);
/* in pt.c */
extern bool check_template_shadow (tree);
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 99f0af2..51a5305 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -8724,6 +8724,7 @@ grokfndecl (tree ctype,
if (DECL_LANGUAGE (decl) == lang_c)
{
error ("literal operator with C linkage");
+ maybe_show_extern_c_location ();
return NULL_TREE;
}
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 28bc8e4..a556a21 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -3828,6 +3828,9 @@ cp_parser_new (void)
/* Allow constrained-type-specifiers. */
parser->prevent_constrained_type_specifiers = 0;
+ /* We haven't yet seen an 'extern "C"'. */
+ parser->innermost_linkage_specification_location = UNKNOWN_LOCATION;
+
return parser;
}
@@ -13740,6 +13743,7 @@ cp_parser_linkage_specification (cp_parser* parser)
cp_parser_require_keyword (parser, RID_EXTERN, RT_EXTERN);
/* Look for the string-literal. */
+ cp_token *string_token = cp_lexer_peek_token (parser->lexer);
linkage = cp_parser_string_literal (parser, false, false);
/* Transform the literal into an identifier. If the literal is a
@@ -13758,6 +13762,13 @@ cp_parser_linkage_specification (cp_parser* parser)
/* We're now using the new linkage. */
push_lang_context (linkage);
+ /* Preserve the location of the string-literal for the innermost linkage
+ specification, tracking the locations of nested specifications
+ via a local. */
+ location_t saved_location
+ = parser->innermost_linkage_specification_location;
+ parser->innermost_linkage_specification_location = string_token->location;
+
/* If the next token is a `{', then we're using the first
production. */
if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
@@ -13788,6 +13799,9 @@ cp_parser_linkage_specification (cp_parser* parser)
/* We're done with the linkage-specification. */
pop_lang_context ();
+
+ /* Restore location of parent linkage specification, if any. */
+ parser->innermost_linkage_specification_location = saved_location;
}
/* Parse a static_assert-declaration.
@@ -16537,6 +16551,7 @@ cp_parser_explicit_specialization (cp_parser* parser)
if (current_lang_name == lang_name_c)
{
error_at (token->location, "template specialization with C linkage");
+ maybe_show_extern_c_location ();
/* Give it C++ linkage to avoid confusing other parts of the
front end. */
push_lang_context (lang_name_cplusplus);
@@ -26861,6 +26876,7 @@ cp_parser_explicit_template_declaration (cp_parser*
parser, bool member_p)
if (current_lang_name == lang_name_c)
{
error_at (location, "template with C linkage");
+ maybe_show_extern_c_location ();
/* Give it C++ linkage to avoid confusing other parts of the
front end. */
push_lang_context (lang_name_cplusplus);
@@ -39479,4 +39495,17 @@ finish_fully_implicit_template (cp_parser *parser,
tree member_decl_opt)
return member_decl_opt;
}
+/* Helper function for diagnostics that have complained about things
+ being used with 'extern "C"' linkage.
+
+ Attempt to issue a note showing where the 'extern "C"' linkage began. */
+
+void
+maybe_show_extern_c_location (void)
+{
+ if (the_parser->innermost_linkage_specification_location != UNKNOWN_LOCATION)
+ inform (the_parser->innermost_linkage_specification_location,
+ "%<extern \"C\"%> linkage started here");
+}
+
#include "gt-cp-parser.h"
diff --git a/gcc/cp/parser.h b/gcc/cp/parser.h
index 0994e1e..f4f4a01 100644
--- a/gcc/cp/parser.h
+++ b/gcc/cp/parser.h
@@ -412,6 +412,10 @@ struct GTY(()) cp_parser {
context e.g., because they could never be deduced. */
int prevent_constrained_type_specifiers;
+ /* Location of the string-literal token within the current linkage
+ specification, if any, or UNKNOWN_LOCATION otherwise. */
+ location_t innermost_linkage_specification_location;
+
};
/* In parser.c */
diff --git a/gcc/testsuite/g++.dg/cpp0x/udlit-extern-c.C
b/gcc/testsuite/g++.dg/cpp0x/udlit-extern-c.C
new file mode 100644
index 0000000..ea54cba
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/udlit-extern-c.C
@@ -0,0 +1,7 @@
+// { dg-do compile { target c++11 } }
+
+extern "C" { // { dg-message "8: 'extern .C.' linkage started here" }
+
+constexpr double operator"" _deg ( double degrees ); // { dg-error "literal
operator with C linkage" }
+
+}
diff --git a/gcc/testsuite/g++.dg/diagnostic/unclosed-extern-c.C
b/gcc/testsuite/g++.dg/diagnostic/unclosed-extern-c.C
index fda3532..d85a049 100644
--- a/gcc/testsuite/g++.dg/diagnostic/unclosed-extern-c.C
+++ b/gcc/testsuite/g++.dg/diagnostic/unclosed-extern-c.C
@@ -1,3 +1,12 @@
-extern "C" { /* { dg-message "12: to match this '.'" } */
+extern "C" { // { dg-line open_extern_c }
+
+ int foo (void);
+
+/* Missing close-brace for the extern "C" here. */
+
+template <typename T> // { dg-error "template with C linkage" }
+void bar (void);
+// { dg-message "8: 'extern .C.' linkage started here" "" { target *-*-* }
open_extern_c }
void test (void); /* { dg-error "17: expected '.' at end of input" } */
+// { message "12: to match this '.'" "" { target *-*-* } open_extern_c }
diff --git a/gcc/testsuite/g++.dg/template/extern-c.C
b/gcc/testsuite/g++.dg/template/extern-c.C
new file mode 100644
index 0000000..6cbf69f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/extern-c.C
@@ -0,0 +1,66 @@
+template <typename T> void specializable (T);
+
+/* Invalid template: within "extern C". */
+
+extern "C" { // { dg-message "8: 'extern .C.' linkage started here" }
+
+template <typename T> // { dg-error "template with C linkage" }
+void within_extern_c_braces (void);
+
+}
+
+/* Valid template: not within "extern C". */
+
+template <typename T>
+void not_within_extern_c (void);
+
+
+/* Invalid specialization: within "extern C". */
+
+extern "C" { // { dg-message "8: 'extern .C.' linkage started here" }
+
+template <> // { dg-error "template specialization with C linkage" }
+void specializable (int);
+
+}
+
+
+/* Valid specialization: not within "extern C". */
+template <>
+void specializable (char);
+
+
+/* Example of extern C without braces. */
+
+extern "C" template <typename T> // { dg-line open_extern_c_no_braces }
+void within_extern_c_no_braces (void);
+// { dg-error "12: template with C linkage" "" { target *-*-* }
open_extern_c_no_braces }
+// { dg-message "8: 'extern .C.' linkage started here" "" { target *-*-* }
open_extern_c_no_braces }
+
+
+/* Nested extern "C" specifications.
+ We should report within the innermost extern "C" that's still open. */
+
+extern "C" {
+ extern "C" { // { dg-line middle_open_extern_c }
+ extern "C" {
+ }
+
+ template <typename T> // { dg-error "template with C linkage" }
+ void within_nested_extern_c (void);
+ // { dg-message "10: 'extern .C.' linkage started here" "" { target *-*-*
} middle_open_extern_c }
+
+ extern "C++" {
+ /* Valid template: within extern "C++". */
+ template <typename T>
+ void within_nested_extern_cpp (void);
+
+ extern "C" { // { dg-line last_open_extern_c }
+ /* Invalid template: within "extern C". */
+ template <typename T> // { dg-error "template with C linkage" }
+ void within_extern_c_within_extern_cpp (void);
+ // { dg-message "14: 'extern .C.' linkage started here" "" { target
*-*-* } last_open_extern_c }
+ }
+ }
+ }
+}
--
1.8.5.3
