Add basedir config to reuse cache from different directories

caches/cache.go

@@ -53,7 +53,8 @@ func computeDigestForClangTidyBinary(clangTidyPath string) ([]byte, error) {
 	return computeFileDigest(path)
 }
 
-func ComputeFingerPrint(clangTidyPath string, invocation *clang.TidyInvocation, wd string, args []string) ([]byte, error) {
+func ComputeFingerPrint(clangTidyPath string, baseDir 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)
@@ -68,7 +69,7 @@ func ComputeFingerPrint(clangTidyPath string, invocation *clang.TidyInvocation,
 	}
 
 	// main part of the fingerprint check generate the preprocessed output file and create a SHA256 of it
-	preProcessedDigest, err := clang.EvaluatePreprocessedFile(targetFlags.Directory, compileCommand)
+	preProcessedDigest, err := clang.EvaluatePreprocessedFile(targetFlags.Directory, baseDir, compileCommand)
 	if err != nil {
 		return nil, err
 	}

clang/clangArgumentParser.go

@@ -1,6 +1,7 @@
 package clang
 
 import (
+	"bytes"
 	"crypto/sha256"
 	"errors"
 	"io"
@@ -52,7 +53,7 @@ func ParseClangCommandString(commands string) (*CompilerCommand, error) {
 	return &cmd, nil
 }
 
-func EvaluatePreprocessedFile(buildRoot string, command *CompilerCommand) ([]byte, error) {
+func EvaluatePreprocessedFile(buildRoot string, baseDir string, command *CompilerCommand) ([]byte, error) {
 	// make the temporary file
 	tmpfile, err := ioutil.TempFile("", "ctc-")
 	if err != nil {
@@ -71,7 +72,8 @@ func EvaluatePreprocessedFile(buildRoot string, command *CompilerCommand) ([]byt
 	// build up all of the args
 	args := make([]string, 0, len(command.Arguments)+10)
 	args = append(args, command.Arguments...)
-	args = append(args, "-E", "-o", filename, command.InputPath)
+	// the -P flag drops linemarkers which contain absolute paths to headers
+	args = append(args, "-E", "-P", "-o", filename, command.InputPath)
 
 	// run the preprocessor
 	cmd := exec.Command(command.Compiler, args...)
@@ -82,15 +84,23 @@ func EvaluatePreprocessedFile(buildRoot string, command *CompilerCommand) ([]byt
 	}
 
 	// read the contents of the file am hash it
-	f, err := os.Open(filename)
-	if err != nil {
-		return nil, err
-	}
-	defer f.Close()
-
 	hasher := sha256.New()
-	if _, err := io.Copy(hasher, f); err != nil {
-		return nil, err
+	if len(baseDir) == 0 {
+		f, err := os.Open(filename)
+		if err != nil {
+			return nil, err
+		}
+		defer f.Close()
+
+		if _, err := io.Copy(hasher, f); err != nil {
+			return nil, err
+		}
+	} else {
+		data, err := ioutil.ReadFile(filename)
+		if err != nil {
+			return nil, err
+		}
+		hasher.Write(bytes.ReplaceAll(data, []byte(baseDir), []byte(".")))
 	}
 
 	// compute the final digest

main.go

@@ -11,12 +11,14 @@ import (
 	"os/exec"
 	"os/user"
 	"path"
+	"path/filepath"
 )
 
 const VERSION = "0.3.0"
 
 type Configuration struct {
 	ClangTidyPath string                   `json:"clang_tidy_path"`
+	BaseDir       string                   `json:"base_dir"`
 	GcsConfig     *caches.GcsConfiguration `json:"gcs,omitempty"`
 }
 
@@ -61,6 +63,9 @@ func readConfigEnv(cfg *Configuration) {
 	if envPath := os.Getenv("CLANG_TIDY_CACHE_BINARY"); len(envPath) > 0 {
 		cfg.ClangTidyPath = envPath
 	}
+	if envBaseDir := os.Getenv("CLANG_TIDY_CACHE_BASEDIR"); len(envBaseDir) > 0 {
+		cfg.BaseDir = filepath.Clean(envBaseDir)
+	}
 }
 
 func loadConfiguration() (*Configuration, error) {
@@ -152,7 +157,7 @@ func evaluateTidyCommand(cfg *Configuration, wd string, args []string, cache cac
 		invocation = other
 
 		// compute the finger print for the file
-		computedFingerPrint, err := caches.ComputeFingerPrint(cfg.ClangTidyPath, invocation, wd, args)
+		computedFingerPrint, err := caches.ComputeFingerPrint(cfg.ClangTidyPath, cfg.BaseDir, invocation, wd, args)
 		if err != nil {
 			return err
 		}