fix(overlays): skip .git directory when applying file-targeting overlays (#64)

Author: dmcilvaney

internal/app/azldev/core/sources/overlays.go

@@ -438,12 +438,20 @@ func globNonSpecFiles(destFS opctx.FS, pattern string) ([]string, error) {
 		return nil, fmt.Errorf("failed to glob for files using pattern %#q:\n%w", pattern, err)
 	}
 
-	// Filter out .spec files. Paths are already in pseudo-absolute format.
+	// Filter out .spec files and .git directory contents. Paths are already in pseudo-absolute format.
+	// The .git directory is excluded because overlay glob patterns like "**/*" must not match
+	// git internal files (packfiles, objects, etc.) which are read-only and binary.
 	return lo.Filter(candidatePaths, func(path string, _ int) bool {
-		return !isSpecFile(path)
+		return !isSpecFile(path) && !isGitInternalPath(path)
 	}), nil
 }
 
+// isGitInternalPath returns true if the given path is inside a .git directory.
+// Handles both root-level (.git/HEAD) and nested (subdir/.git/objects) paths.
+func isGitInternalPath(path string) bool {
+	return strings.HasPrefix(path, ".git/") || strings.Contains(path, "/.git/")
+}
+
 // newDestFS creates a destination filesystem confined to the given root directory.
 // For real filesystems (OsFs), it uses os.Root via rootfs.RootFs for atomic symlink safety.
 // For test filesystems (MemMapFs), it uses afero.BasePathFs to confine paths.

internal/app/azldev/core/sources/overlays_internal_test.go

@@ -0,0 +1,44 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+package sources
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIsGitInternalPath(t *testing.T) {
+	tests := []struct {
+		path     string
+		expected bool
+	}{
+		// Root-level .git directory contents.
+		{".git/HEAD", true},
+		{".git/config", true},
+		{".git/objects/pack/pack-abc.idx", true},
+
+		// Pseudo-absolute root-level .git paths (/prefix from BasePathFs).
+		{"/.git/HEAD", true},
+		{"/.git/objects/pack/pack-abc.idx", true},
+
+		// Nested .git directories (e.g., submodules).
+		{"subdir/.git/HEAD", true},
+		{"vendor/lib/.git/objects/pack-abc.idx", true},
+
+		// Non-.git paths that should NOT match.
+		{".gitignore", false},
+		{".gitattributes", false},
+		{"foo.spec", false},
+		{"src/main.go", false},
+		{"git/config", false},
+		{"my.gitconfig", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.path, func(t *testing.T) {
+			assert.Equal(t, tt.expected, isGitInternalPath(tt.path))
+		})
+	}
+}