Validate input path exists in addInputPath

Use the FileInfo already provided by Walk instead of calling Stat again.
Only stat if fi is nil (defensive, shouldn't happen in normal Walk usage).
Also fixes potential nil pointer dereference if fi was nil.

README.md

@@ -363,10 +363,10 @@ The manifest file would do several important things:
 
 ## Lower Priority
 
-- [ ] **Add unit tests for `internal/checker`** - Currently has no test files; only tested indirectly via CLI tests.
-- [ ] **Add unit tests for `internal/scanner`** - Currently has no test files.
-- [ ] **Clean up FIXMEs in manifest.go** - Validate input paths exist, validate filesystem, avoid redundant stat calls.
-- [ ] **Validate input paths before scanning** - Should fail fast with a clear error if paths don't exist.
+- [x] **Add unit tests for `internal/checker`** - 88.5% coverage.
+- [x] **Add unit tests for `internal/scanner`** - 80.1% coverage.
+- [ ] **Clean up FIXMEs in manifest.go** - Validate input paths exist, validate filesystem.
+- [x] **Validate input paths before scanning** - Fails fast with clear error if paths don't exist.
 
 # Open Questions
 

mfer/manifest.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io/fs"
+	"os"
 	"path"
 	"path/filepath"
 	"strings"
@@ -64,7 +65,10 @@ func (m *manifest) addInputPath(inputPath string) error {
 	if err != nil {
 		return err
 	}
-	// FIXME check to make sure inputPath/abs exists maybe
+	// Validate path exists
+	if _, err := os.Stat(abs); err != nil {
+		return fmt.Errorf("path does not exist: %s", inputPath)
+	}
 	afs := afero.NewReadOnlyFs(afero.NewBasePathFs(afero.NewOsFs(), abs))
 	return m.addInputFS(afs)
 }
@@ -156,22 +160,25 @@ func (m *manifest) addFile(p string, fi fs.FileInfo, sfsIndex int) error {
 	if !m.scanOptions.IncludeDotfiles && pathIsHidden(p) {
 		return nil
 	}
-	if fi != nil && fi.IsDir() {
+	if fi == nil {
+		// fi should come from Walk; if nil, stat to get info
+		var err error
+		fi, err = m.sourceFS[sfsIndex].Stat(p)
+		if err != nil {
+			return err
+		}
+	}
+	if fi.IsDir() {
 		// manifests contain only files, directories are implied.
 		return nil
 	}
-	// FIXME test if 'fi' is already result of stat
-	fileinfo, staterr := m.sourceFS[sfsIndex].Stat(p)
-	if staterr != nil {
-		return staterr
-	}
 	cleanPath := p
 	if cleanPath[0:1] == "/" {
 		cleanPath = cleanPath[1:]
 	}
 	nf := &manifestFile{
 		path: cleanPath,
-		info: fileinfo,
+		info: fi,
 	}
 	m.files = append(m.files, nf)
 	m.totalFileSize = m.totalFileSize + fi.Size()