From 15f7a4692667ce38eed325a9567f5ef492a5ce07 Mon Sep 17 00:00:00 2001 From: David Malcolm Date: Fri, 13 Oct 2017 12:42:39 +0000 Subject: [PATCH] C++: show location of unclosed extern "C" specifications 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 linkage specification 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. From-SVN: r253726 --- gcc/cp/ChangeLog | 18 +++++ gcc/cp/cp-tree.h | 1 + gcc/cp/decl.c | 1 + gcc/cp/parser.c | 39 ++++++++++- gcc/cp/parser.h | 4 ++ gcc/testsuite/ChangeLog | 7 ++ 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 +++++++++++++++++++ 9 files changed, 152 insertions(+), 2 deletions(-) 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/ChangeLog b/gcc/cp/ChangeLog index 3abf79440cc..c22583554e5 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,3 +1,21 @@ +2017-10-13 David Malcolm + + * 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 linkage specification 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". + 2017-10-12 Nathan Sidwell * cp-tree.h (cp_expr): Add const operator * and operator-> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index dc98dd881c5..b74b6d9d950 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -6356,6 +6356,7 @@ 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 f251a9043d4..a3cc80cf7a3 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -8729,6 +8729,7 @@ 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 810e2b7f72e..2337be52c38 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -3937,6 +3937,9 @@ 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; } @@ -13848,9 +13851,11 @@ cp_parser_linkage_specification (cp_parser* parser) tree linkage; /* Look for the `extern' keyword. */ - cp_parser_require_keyword (parser, RID_EXTERN, RT_EXTERN); + cp_token *extern_token + = 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 @@ -13869,6 +13874,20 @@ cp_parser_linkage_specification (cp_parser* parser) /* We're now using the new linkage. */ push_lang_context (linkage); + /* Preserve the location of the the innermost linkage specification, + tracking the locations of nested specifications via a local. */ + location_t saved_location + = parser->innermost_linkage_specification_location; + /* Construct a location ranging from the start of the "extern" to + the end of the string-literal, with the caret at the start, e.g.: + extern "C" { + ^~~~~~~~~~ + */ + parser->innermost_linkage_specification_location + = make_location (extern_token->location, + extern_token->location, + get_finish (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)) @@ -13899,6 +13918,9 @@ 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. @@ -16643,6 +16665,7 @@ 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); @@ -26979,6 +27002,7 @@ 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); @@ -39552,4 +39576,17 @@ 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, + "% linkage started here"); +} + #include "gt-cp-parser.h" diff --git a/gcc/cp/parser.h b/gcc/cp/parser.h index 0994e1e7f4f..f4f4a010964 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/ChangeLog b/gcc/testsuite/ChangeLog index 90a7f722111..6bb877ea387 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,10 @@ +2017-10-13 David Malcolm + + * 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. + 2017-10-13 Richard Biener * gcc.dg/graphite/pr35356-3.c: XFAIL again. 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 00000000000..d47a49c3fa8 --- /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 "1: '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 fda3532266d..44f538e33ec 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 // { dg-error "template with C linkage" } +void bar (void); +// { dg-message "1: '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 00000000000..c0dd7cb66d5 --- /dev/null +++ b/gcc/testsuite/g++.dg/template/extern-c.C @@ -0,0 +1,66 @@ +template void specializable (T); + +/* Invalid template: within "extern C". */ + +extern "C" { // { dg-message "1: 'extern .C.' linkage started here" } + +template // { dg-error "template with C linkage" } +void within_extern_c_braces (void); + +} + +/* Valid template: not within "extern C". */ + +template +void not_within_extern_c (void); + + +/* Invalid specialization: within "extern C". */ + +extern "C" { // { dg-message "1: '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 // { 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 "1: '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 // { dg-error "template with C linkage" } + void within_nested_extern_c (void); + // { dg-message "3: 'extern .C.' linkage started here" "" { target *-*-* } middle_open_extern_c } + + extern "C++" { + /* Valid template: within extern "C++". */ + template + void within_nested_extern_cpp (void); + + extern "C" { // { dg-line last_open_extern_c } + /* Invalid template: within "extern C". */ + template // { dg-error "template with C linkage" } + void within_extern_c_within_extern_cpp (void); + // { dg-message "7: 'extern .C.' linkage started here" "" { target *-*-* } last_open_extern_c } + } + } + } +} -- 2.30.2