Add C example and file extension. (#349)

* Add C example and file extension.

* First class support for C formatting.

* Update starlark docs.

example/src/BUILD.bazel

@@ -78,6 +78,11 @@ cc_binary(
     srcs = ["hello.cpp"],
 )
 
+cc_binary(
+    name = "hello_c",
+    srcs = ["hello.c"],
+)
+
 kt_jvm_library(
     name = "hello_kt",
     srcs = ["hello.kt"],

example/src/hello.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// deliberately bad code to trigger clang-tidy warning
+int string_to_int(const char *num) { return atoi(num); }
+
+// deliberately insecure code to trigger clang-tidy warning
+void ls() { system("ls"); }
+
+static int compare(int x, int y) {
+  if (x < y)
+    ;
+  { x++; }
+  return x;
+}
+
+int main() {
+  printf("Hello, world!\n");
+  compare(3, 4);
+  char *a = NULL;
+  char *b = 0;
+}

example/tools/format/BUILD.bazel

@@ -57,6 +57,7 @@ java_binary(
 
 format_multirun(
     name = "format",
+    c = "@llvm_toolchain_llvm//:bin/clang-format",
     cc = "@llvm_toolchain_llvm//:bin/clang-format",
     css = ":prettier",
     cuda = "@llvm_toolchain_llvm//:bin/clang-format",

format/private/format.sh

@@ -66,6 +66,7 @@ function ls-files {
     # https://github.com/github-linguist/linguist/blob/559a6426942abcae16b6d6b328147476432bf6cb/lib/linguist/languages.yml
     # using the ./mirror_linguist_languages.sh tool to transform to Bash code
     case "$language" in
+      'C') patterns=('*.c' '*.cats' '*.h' '*.idc') ;;
       'C++') patterns=('*.cpp' '*.c++' '*.cc' '*.cp' '*.cppm' '*.cxx' '*.h' '*.h++' '*.hh' '*.hpp' '*.hxx' '*.inc' '*.inl' '*.ino' '*.ipp' '*.ixx' '*.re' '*.tcc' '*.tpp' '*.txx') ;;
       'Cuda') patterns=('*.cu' '*.cuh') ;;
       'CSS') patterns=('*.css') ;;

format/private/formatter_binary.bzl

@@ -21,6 +21,7 @@ TOOLS = {
     "SQL": "prettier",
     "Shell": "shfmt",
     "Protocol Buffer": "buf",
+    "C": "clang-format",
     "C++": "clang-format",
     "Cuda": "clang-format",
     "YAML": "yamlfmt",