Add debug mode (#95)

Why:
We want to provide useful debug messages to users without cluttering the
default output.

What:
Added a new tag `"debug"`, which, if set allows calls of the `warning`
function to print debug messages.

Addresses:
fixes: #94

Author: furtib

src/codechecker.bzl

@@ -14,6 +14,10 @@ load(
     "per_file.bzl",
     "per_file_test",
 )
+load(
+    "tools.bzl",
+    "warning"
+)
 
 def get_platform_alias(platform):
     """

src/per_file.bzl

@@ -3,6 +3,7 @@
 
 load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "ACTION_NAMES")
 load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain")
+load("@bazel_codechecker//src:tools.bzl", "warning")
 
 def _run_code_checker(
         ctx,
@@ -182,8 +183,7 @@ def _compile_info_aspect_impl(target, ctx):
         elif src.extension.lower() in ["cc", "cpp", "cxx", "c++"]:
             flags = cxx_flags
         else:
-            # FIXME: Create verbose mode, show warning only if thats enabled
-            print(
+            warning(
                 "Unknown file extension for {} defaulting to c++ compile flags".
                 format(src.short_path)
                 )

src/tools.bzl

@@ -98,3 +98,10 @@ default_codechecker_tools = repository_rule(
 
 def register_default_codechecker():
     default_codechecker_tools(name = "default_codechecker_tools")
+
+def warning(ctx, msg):
+    """
+    Prints message if the debug tag is enabled.
+    """
+    if "debug" in ctx.attr.tags:
+        print(msg)