Include clang-tidy binary in the cache fingerprint

README.md

@@ -4,7 +4,7 @@ A fairly simple wrapper application around the clang-tidy executable. It will at
 
 ## Configuration
 
-In order to keep the wrapper reasonably clean, the user will have to write a configuration file at the following location:
+By default, the wrapper will look for the `clang-tidy` executable on the path. This can be changed by setting the `CLANG_TIDY_CACHE_BINARY` environment variable, or by writing a configuration file at the following location:
 
 `~/.ctcache/config.json`
 

caches/cache.go

@@ -6,6 +6,7 @@ import (
 	"github.com/ejfitzgerald/clang-tidy-cache/utils"
 	"io"
 	"os"
+	"os/exec"
 )
 
 type Cacher interface {
@@ -15,15 +16,8 @@ type Cacher interface {
 	SaveEntry(digest []byte, content []byte) error
 }
 
-func computeDigestForConfigFile(projectRoot string) ([]byte, error) {
-	configFilePath, err := utils.FindInParents(projectRoot, ".clang-tidy")
-	if err != nil {
-		return nil, err
-	}
-
-	// compute the SHA of the configuration file
-	// read the contents of the file am hash it
-	f, err := os.Open(configFilePath)
+func computeFileDigest(path string) ([]byte, error) {
+	f, err := os.Open(path)
 	if err != nil {
 		return nil, err
 	}
@@ -40,7 +34,26 @@ func computeDigestForConfigFile(projectRoot string) ([]byte, error) {
 	return digest, nil
 }
 
-func ComputeFingerPrint(invocation *clang.TidyInvocation, wd string, args []string) ([]byte, error) {
+func computeDigestForConfigFile(projectRoot string) ([]byte, error) {
+	configFilePath, err := utils.FindInParents(projectRoot, ".clang-tidy")
+	if err != nil {
+		return nil, err
+	}
+
+	return computeFileDigest(configFilePath)
+}
+
+func computeDigestForClangTidyBinary(clangTidyPath string) ([]byte, error) {
+	// resolve to a full path: e.g. `clang-tidy` -> `/usr/local/bin/clang-tidy`
+	path, err := exec.LookPath(clangTidyPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return computeFileDigest(path)
+}
+
+func ComputeFingerPrint(clangTidyPath string, invocation *clang.TidyInvocation, wd string, args []string) ([]byte, error) {
 
 	// extract the compilation target command flags from the database
 	targetFlags, err := clang.ExtractCompilationTarget(invocation.DatabaseRoot, invocation.TargetPath)
@@ -66,10 +79,17 @@ func ComputeFingerPrint(invocation *clang.TidyInvocation, wd string, args []stri
 		return nil, err
 	}
 
+	// we also need to include the clang-tidy binary since different version have different output
+	binaryDigest, err := computeDigestForClangTidyBinary(clangTidyPath)
+	if err != nil {
+		return nil, err
+	}
+
 	// combine all the digests to generate a unique fingerprint
 	hasher := sha256.New()
 	hasher.Write(preProcessedDigest)
 	hasher.Write(configDigest)
+	hasher.Write(binaryDigest)
 	fingerPrint := hasher.Sum(nil)
 
 	return fingerPrint, nil

main.go

@@ -20,33 +20,62 @@ type Configuration struct {
 	GcsConfig     *caches.GcsConfiguration `json:"gcs,omitempty"`
 }
 
-func loadConfiguration() (*Configuration, error) {
+func readConfigFile(cfg *Configuration) error {
 	usr, err := user.Current()
 	if err != nil {
-		return nil, err
+		return err
 	}
 
 	// define the configuration path
 	configPath := path.Join(usr.HomeDir, ".ctcache", "config.json")
 
+	// missing config file is fine: we simply use the defaults or env vars
+	if _, err := os.Stat(configPath); os.IsNotExist(err) {
+		return nil
+	}
+
 	// open the configuration file
 	jsonFile, err := os.Open(configPath)
 	if err != nil {
-		return nil, err
+		return err
 	}
 
 	// defer the closing of our jsonFile so that we can parse it later on
 	defer jsonFile.Close()
 
 	// read the contents
 	bytes, err := ioutil.ReadAll(jsonFile)
+	if err != nil {
+		return err
+	}
 
-	var cfg Configuration
-	err = json.Unmarshal(bytes, &cfg)
+	err = json.Unmarshal(bytes, cfg)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func readConfigEnv(cfg *Configuration) {
+	if envPath := os.Getenv("CLANG_TIDY_CACHE_BINARY"); len(envPath) > 0 {
+		cfg.ClangTidyPath = envPath
+	}
+}
+
+func loadConfiguration() (*Configuration, error) {
+	// lowest priority: built-in defaults
+	cfg := Configuration{ClangTidyPath: "clang-tidy"}
+
+	// higher priority: config file
+	err := readConfigFile(&cfg)
 	if err != nil {
 		return nil, err
 	}
 
+	// highest priority: environment variables
+	readConfigEnv(&cfg)
+
 	return &cfg, nil
 }
 
@@ -123,7 +152,7 @@ func evaluateTidyCommand(cfg *Configuration, wd string, args []string, cache cac
 		invocation = other
 
 		// compute the finger print for the file
-		computedFingerPrint, err := caches.ComputeFingerPrint(invocation, wd, args)
+		computedFingerPrint, err := caches.ComputeFingerPrint(cfg.ClangTidyPath, invocation, wd, args)
 		if err != nil {
 			return err
 		}