Fix FindChangedFiles

tools/flakeguard/utils/git.go

@@ -5,29 +5,64 @@ import (
 	"fmt"
 	"os/exec"
 	"strings"
+	"syscall"
 )
 
 // FindChangedFiles executes a git diff against a specified base reference and pipes the output through a user-defined grep command or sequence.
 // The baseRef parameter specifies the base git reference for comparison (e.g., "main", "develop").
-// The grepCmd parameter should include the full command to be executed after git diff, such as "grep '_test.go$'" or "grep -v '_test.go$' | sort".
-func FindChangedFiles(repoPath, baseRef, grepCmd string) ([]string, error) {
-	cmdString := fmt.Sprintf("git diff --name-only --diff-filter=AM %s...HEAD | %s", baseRef, grepCmd)
-	cmd := exec.Command("bash", "-c", cmdString)
-	cmd.Dir = repoPath
+// The filterCmd parameter should include the full command to be executed after git diff, such as "grep '_test.go$'" or "grep -v '_test.go$' | sort".
+func FindChangedFiles(repoPath, baseRef, filterCmd string) ([]string, error) {
+	// First command to list files changed between the baseRef and HEAD
+	diffCmdStr := fmt.Sprintf("git diff --name-only --diff-filter=AM %s...HEAD", baseRef)
+	diffCmd := exec.Command("bash", "-c", diffCmdStr)
+	diffCmd.Dir = repoPath
 
-	// Using a buffer to capture both stdout and stderr
+	// Using a buffer to capture stdout and a separate buffer for stderr
 	var out bytes.Buffer
-	cmd.Stdout = &out
-	cmd.Stderr = &out // Capturing stderr in the same buffer as stdout
+	var errBuf bytes.Buffer
+	diffCmd.Stdout = &out
+	diffCmd.Stderr = &errBuf
 
-	// Running the command
-	if err := cmd.Run(); err != nil {
-		return nil, fmt.Errorf("error executing command: %w; output: %s", err, out.String())
+	// Running the diff command
+	if err := diffCmd.Run(); err != nil {
+		return nil, fmt.Errorf("error executing git diff command: %s; error: %w; stderr: %s", diffCmdStr, err, errBuf.String())
 	}
 
+	// Check if there are any files listed, if not, return an empty slice
+	diffOutput := strings.TrimSpace(out.String())
+	if diffOutput == "" {
+		return []string{}, nil
+	}
+
+	// Second command to filter files using grepCmd
+	grepCmdStr := fmt.Sprintf("echo '%s' | %s", diffOutput, filterCmd)
+	grepCmd := exec.Command("bash", "-c", grepCmdStr)
+	grepCmd.Dir = repoPath
+
+	// Reset buffers for reuse
+	out.Reset()
+	errBuf.Reset()
+	grepCmd.Stdout = &out
+	grepCmd.Stderr = &errBuf
+
+	// Running the grep command
+	if err := grepCmd.Run(); err != nil {
+		if exiterr, ok := err.(*exec.ExitError); ok {
+			if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
+				if status.ExitStatus() == 1 {
+					// Exit status 1 for grep means no lines matched, which is not an error in this context
+					return []string{}, nil
+				}
+			}
+		}
+		return nil, fmt.Errorf("error executing grep command: %s; error: %w; stderr: %s", grepCmdStr, err, errBuf.String())
+	}
+
+	// Preparing the final list of files
 	files := strings.Split(strings.TrimSpace(out.String()), "\n")
 	if len(files) == 1 && files[0] == "" {
 		return []string{}, nil
 	}
+
 	return files, nil
 }