Use number of issues as exit code

Author: mpeterv

spec/cli_spec.lua

@@ -117,7 +117,7 @@ Checking spec/samples/bad_code.lua                5 warnings
 
 Total: 5 warnings / 0 errors in 1 file
 ]], get_output "spec/samples/bad_code.lua --no-config")
-      assert.equal(1, get_exitcode "spec/samples/bad_code.lua --no-config")
+      assert.equal(5, get_exitcode "spec/samples/bad_code.lua --no-config")
    end)
 
    it("detects whitespace issues", function()
@@ -135,7 +135,7 @@ Checking spec/samples/bad_whitespace.lua          8 warnings
 
 Total: 8 warnings / 0 errors in 1 file
 ]], get_output "spec/samples/bad_whitespace.lua --no-config")
-      assert.equal(1, get_exitcode "spec/samples/bad_whitespace.lua --no-config")
+      assert.equal(8, get_exitcode "spec/samples/bad_whitespace.lua --no-config")
    end)
 
    it("works for incorrect patterns in options", function()
@@ -1216,11 +1216,11 @@ Critical error: Couldn't find configuration file spec/configs/config_404.luachec
 
       describe("overwriting", function()
          it("prioritizes CLI options over config", function()
-            assert.equal(1, get_exitcode "spec/samples/compat.lua --config=spec/configs/cli_override_config.luacheckrc --new-globals foo")
+            assert.is_true(get_exitcode "spec/samples/compat.lua --config=spec/configs/cli_override_config.luacheckrc --new-globals foo" > 0)
          end)
 
          it("prioritizes CLI options over config overrides", function()
-            assert.equal(1, get_exitcode "spec/samples/compat.lua --config=spec/configs/cli_override_file_config.luacheckrc --new-globals foo")
+            assert.is_true(get_exitcode "spec/samples/compat.lua --config=spec/configs/cli_override_file_config.luacheckrc --new-globals foo" > 0)
          end)
 
          it("concats array-like options from config and CLI", function()

src/luacheck/main.lua

@@ -523,16 +523,7 @@ patterns.]])
 
    io.stdout:write(output)
 
-   local exit_code
-
-   if report.fatals > 0 then
-      exit_code = 2
-   elseif report.warnings > 0 or report.errors > 0 then
-      exit_code = 1
-   else
-      exit_code = 0
-   end
-
+   local exit_code = math.min(report.fatals + report.errors + report.warnings, 255)
    os.exit(exit_code)
 end