cc-mode: extend regexp used by ‘c-or-c++-mode’

* lisp/progmodes/cc-mode (c-or-c++-mode--regexp): Expand the regexp to
match some more C++-only constructs and recognise a few more standard
C++ header files.  Also make sure identifiers start with non-digit.
(c-or-c++-mode): Add ‘(interactive)’ declaration.

* test/lisp/progmodes/cc-mode-tests.el (c-or-c++-mode): Add test case
for the newly recognised constructs.

2 files changed, 25 insertions, 8 deletions

diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index f92d3efdeb7..e3a924efb06 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -2541,13 +2541,21 @@ Key bindings:
 
 (defconst c-or-c++-mode--regexp
   (eval-when-compile
-    (let ((id "[a-zA-Z0-9_]+") (ws "[ \t\r]+") (ws-maybe "[ \t\r]*"))
+    (let ((id "[a-zA-Z_][a-zA-Z0-9_]*") (ws "[ \t\r]+") (ws-maybe "[ \t\r]*")
+          (headers '("string" "string_view" "iostream" "map" "unordered_map"
+                     "set" "unordered_set" "vector" "tuple")))
       (concat "^" ws-maybe "\\(?:"
-                    "using"     ws "\\(?:namespace" ws "std;\\|std::\\)"
-              "\\|" "namespace" "\\(:?" ws id "\\)?" ws-maybe "{"
-              "\\|" "class"     ws id ws-maybe "[:{\n]"
-              "\\|" "template"  ws-maybe "<.*>"
-              "\\|" "#include"  ws-maybe "<\\(?:string\\|iostream\\|map\\)>"
+                    "using"     ws "\\(?:namespace" ws
+                                     "\\|" id "::"
+                                     "\\|" id ws-maybe "=\\)"
+              "\\|" "\\(?:inline" ws "\\)?namespace"
+                    "\\(:?" ws "\\(?:" id "::\\)*" id "\\)?" ws-maybe "{"
+              "\\|" "class"     ws id
+                    "\\(?:" ws "final" "\\)?" ws-maybe "[:{;\n]"
+              "\\|" "struct"     ws id "\\(?:" ws "final" ws-maybe "[:{\n]"
+                                         "\\|" ws-maybe ":\\)"
+              "\\|" "template"  ws-maybe "<.*?>"
+              "\\|" "#include"  ws-maybe "<" (regexp-opt headers) ">"
               "\\)")))
   "A regexp applied to C header files to check if they are really C++.")
 
@@ -2563,6 +2571,7 @@ should be used.
 This function attempts to use file contents to determine whether
 the code is C or C++ and based on that chooses whether to enable
 `c-mode' or `c++-mode'."
+  (interactive)
   (if (save-excursion
         (save-restriction
           (save-match-data
diff --git a/test/lisp/progmodes/cc-mode-tests.el b/test/lisp/progmodes/cc-mode-tests.el
index ad7a52b40d9..64d52a952b6 100644
--- a/test/lisp/progmodes/cc-mode-tests.el
+++ b/test/lisp/progmodes/cc-mode-tests.el
@@ -40,7 +40,7 @@
                         (insert content)
                         (setq mode nil)
                         (c-or-c++-mode)
-                        (unless(eq expected mode)
+                        (unless (eq expected mode)
                           (ert-fail
                            (format "expected %s but got %s when testing '%s'"
                                    expected mode content)))))
@@ -53,11 +53,18 @@
               (funcall do-test (concat " * " content) 'c-mode))
             '("using \t namespace \t std;"
               "using \t std::string;"
+              "using Foo = Bar;"
               "namespace \t {"
               "namespace \t foo \t {"
-              "class \t Blah_42 \t {"
+              "namespace \t foo::bar \t {"
+              "inline namespace \t foo \t {"
+              "inline namespace \t foo::bar \t {"
               "class \t Blah_42 \t \n"
+              "class \t Blah_42;"
+              "class \t Blah_42 \t final {"
+              "struct \t Blah_42 \t final {"
               "class \t _42_Blah:public Foo {"
+              "struct \t _42_Blah:public Foo {"
               "template \t < class T >"
               "template< class T >"
               "#include <string>"
@@ -67,6 +74,7 @@
       (mapc (lambda (content) (funcall do-test content 'c-mode))
             '("struct \t Blah_42 \t {"
               "struct template {"
+              "struct Blah;"
               "#include <string.h>")))))
 
 (ert-deftest c-mode-macro-comment ()