Add option for additional definitions for Clang [#207]

doc/flycheck.texi

@@ -588,6 +588,10 @@ describe-variable} on the variable name for detailed help):
 Include search path for @code{c/c++-clang}.
 @end defopt
 
+@defopt flycheck-clang-definitions
+Additional preprocessor definitions for @code{c/c++-clang}.
+@end defopt
+
 @defopt flycheck-clang-language-standard
 The language standard for @code{c/c++-clang}.
 @end defopt
@@ -2808,6 +2812,9 @@ completion systems for @code{flycheck-select-checker} at @kbd{C-c ! s}
 @item
 @ghissue{207, Add @code{flycheck-clang-language-standard} to choose the
 language standard for C/C++ syntax checking}
+@item
+@ghissue{207, Add @code{flycheck-clang-definitions} to set additional
+definitions for C/C++ syntax checking}
 @end itemize
 
 @end itemize

flycheck.el

@@ -3224,6 +3224,16 @@ Relative paths are relative to the file being checked."
   :safe #'flycheck-string-list-p
   :package-version '(flycheck . "0.14"))
 
+(flycheck-def-option-var flycheck-clang-definitions nil c/c++-clang
+  "Additional preprocessor definitions for Clang.
+
+The value of this variable is a list of strings, where each
+string is an additional definition to pass to Clang, via the `-D'
+option."
+  :type '(repeat (string :tag "Definition"))
+  :safe #'flycheck-string-list-p
+  :package-version '(flycheck . "0.15"))
+
 (flycheck-def-option-var flycheck-clang-language-standard nil c/c++-clang
   "The language standard to use in Clang.
 
@@ -3265,6 +3275,7 @@ See URL `http://clang.llvm.org/'."
                                         ; warning group
             (option "-std=" flycheck-clang-language-standard)
             (option-list "-W" flycheck-clang-warnings s-prepend)
+            (option-list "-D" flycheck-clang-definitions s-prepend)
             (option-list "-I" flycheck-clang-include-path)
             "-x" (eval
                   (cl-case major-mode

test/builtin-checkers-test.el

@@ -105,17 +105,26 @@
   :expected-result (flycheck-testsuite-fail-unless-checker 'c/c++-clang)
   (flycheck-testsuite-should-syntax-check
    "checkers/c_c++-clang-error.cpp" 'c++-mode nil
-   '(5 18 "implicit instantiation of undefined template 'test<false>'" error)
-   '(6 17 "'nullptr' is a keyword in C++11" warning)
-   '(6 17 "use of undeclared identifier 'nullptr'" error)))
+   '(6 17 "implicit instantiation of undefined template 'test<false>'" error)
+   '(8 16 "'nullptr' is a keyword in C++11" warning)
+   '(8 16 "use of undeclared identifier 'nullptr'" error)))
 
 (ert-deftest checker-c/c++-clang-error-language-standard ()
   :expected-result (flycheck-testsuite-fail-unless-checker 'c/c++-clang)
   (flycheck-testsuite-with-hook c++-mode-hook
       (setq flycheck-clang-language-standard "c++11")
     (flycheck-testsuite-should-syntax-check
      "checkers/c_c++-clang-error.cpp" 'c++-mode nil
-     '(5 18 "implicit instantiation of undefined template 'test<false>'" error))))
+     '(6 17 "implicit instantiation of undefined template 'test<false>'" error))))
+
+(ert-deftest checker-c/c++-clang-error-definitions ()
+  :expected-result (flycheck-testsuite-fail-unless-checker 'c/c++-clang)
+  (flycheck-testsuite-with-hook c++-mode-hook
+      (setq flycheck-clang-definitions '("FOO" "BAR"))
+    (flycheck-testsuite-should-syntax-check
+     "checkers/c_c++-clang-error.cpp" 'c++-mode nil
+     '(8 16 "'nullptr' is a keyword in C++11" warning)
+     '(8 16 "use of undeclared identifier 'nullptr'" error))))
 
 (ert-deftest checker-c/c++-cppcheck-error ()
   :expected-result (flycheck-testsuite-fail-unless-checker 'c/c++-cppcheck)

test/resources/checkers/c_c++-clang-error.cpp

@@ -2,7 +2,9 @@ template<bool> struct test;
 template<> struct test<true> {};
 
 int main(void) {
-     test<false> t;
-     int *foo = nullptr;
-     return 0;
+#if !(defined(FOO) && defined(BAR))
+    test<false> t;
+#endif
+    int *foo = nullptr;
+    return 0;
 }