Add --resolve-symlinks flag to build and push artifact commands

This adds a --resolve-symlinks flag to the flux build artifact and flux push artifact
commands. When enabled, symlinks in the source directory are resolved (copied as regular
files/directories) before building the artifact. This includes:

- Recursive symlink resolution with cycle detection
- File permission preservation
- Proper handling of both single-file and directory symlink targets
- Comprehensive test coverage

Fixes #5055

Signed-off-by: Rohan Sood <56945243+rohansood10@users.noreply.github.com>

cmd/flux/build_artifact_test.go

@@ -18,6 +18,7 @@ package main
 
 import (
 	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -68,3 +69,113 @@ data:
 
 	}
 }
+
+func Test_resolveSymlinks(t *testing.T) {
+	g := NewWithT(t)
+
+	// Create source directory with a real file
+	srcDir := t.TempDir()
+	realFile := filepath.Join(srcDir, "real.yaml")
+	g.Expect(os.WriteFile(realFile, []byte("apiVersion: v1\nkind: Namespace\nmetadata:\n  name: test\n"), 0o644)).To(Succeed())
+
+	// Create a directory with symlinks pointing to files outside it
+	symlinkDir := t.TempDir()
+	symlinkFile := filepath.Join(symlinkDir, "linked.yaml")
+	g.Expect(os.Symlink(realFile, symlinkFile)).To(Succeed())
+
+	// Also add a regular file in the symlink dir
+	regularFile := filepath.Join(symlinkDir, "regular.yaml")
+	g.Expect(os.WriteFile(regularFile, []byte("apiVersion: v1\nkind: ConfigMap\n"), 0o644)).To(Succeed())
+
+	// Create a symlinked subdirectory
+	subDir := filepath.Join(srcDir, "subdir")
+	g.Expect(os.MkdirAll(subDir, 0o755)).To(Succeed())
+	g.Expect(os.WriteFile(filepath.Join(subDir, "nested.yaml"), []byte("nested"), 0o644)).To(Succeed())
+	g.Expect(os.Symlink(subDir, filepath.Join(symlinkDir, "linkeddir"))).To(Succeed())
+
+	// Resolve symlinks
+	resolved, cleanupDir, err := resolveSymlinks(symlinkDir)
+	g.Expect(err).To(BeNil())
+	t.Cleanup(func() { os.RemoveAll(cleanupDir) })
+
+	// Verify the regular file was copied
+	content, err := os.ReadFile(filepath.Join(resolved, "regular.yaml"))
+	g.Expect(err).To(BeNil())
+	g.Expect(string(content)).To(Equal("apiVersion: v1\nkind: ConfigMap\n"))
+
+	// Verify the symlinked file was resolved and copied
+	content, err = os.ReadFile(filepath.Join(resolved, "linked.yaml"))
+	g.Expect(err).To(BeNil())
+	g.Expect(string(content)).To(ContainSubstring("kind: Namespace"))
+
+	// Verify that the resolved file is a regular file, not a symlink
+	info, err := os.Lstat(filepath.Join(resolved, "linked.yaml"))
+	g.Expect(err).To(BeNil())
+	g.Expect(info.Mode().IsRegular()).To(BeTrue())
+
+	// Verify that the symlinked directory was resolved and its contents were copied
+	content, err = os.ReadFile(filepath.Join(resolved, "linkeddir", "nested.yaml"))
+	g.Expect(err).To(BeNil())
+	g.Expect(string(content)).To(Equal("nested"))
+
+	// Verify that the file inside the symlinked directory is a regular file
+	info, err = os.Lstat(filepath.Join(resolved, "linkeddir", "nested.yaml"))
+	g.Expect(err).To(BeNil())
+	g.Expect(info.Mode().IsRegular()).To(BeTrue())
+}
+
+func Test_resolveSymlinks_singleFile(t *testing.T) {
+	g := NewWithT(t)
+
+	// Create a real file
+	srcDir := t.TempDir()
+	realFile := filepath.Join(srcDir, "manifest.yaml")
+	g.Expect(os.WriteFile(realFile, []byte("kind: ConfigMap"), 0o644)).To(Succeed())
+
+	// Create a symlink to the real file
+	linkDir := t.TempDir()
+	linkFile := filepath.Join(linkDir, "link.yaml")
+	g.Expect(os.Symlink(realFile, linkFile)).To(Succeed())
+
+	// Resolve the single symlinked file
+	resolved, cleanupDir, err := resolveSymlinks(linkFile)
+	g.Expect(err).To(BeNil())
+	t.Cleanup(func() { os.RemoveAll(cleanupDir) })
+
+	// The returned path should be a file, not a directory
+	info, err := os.Stat(resolved)
+	g.Expect(err).To(BeNil())
+	g.Expect(info.IsDir()).To(BeFalse())
+
+	// Verify contents
+	content, err := os.ReadFile(resolved)
+	g.Expect(err).To(BeNil())
+	g.Expect(string(content)).To(Equal("kind: ConfigMap"))
+}
+
+func Test_resolveSymlinks_cycle(t *testing.T) {
+	g := NewWithT(t)
+
+	// Create a directory with a symlink cycle: dir/link -> dir
+	dir := t.TempDir()
+	g.Expect(os.WriteFile(filepath.Join(dir, "file.yaml"), []byte("data"), 0o644)).To(Succeed())
+	g.Expect(os.Symlink(dir, filepath.Join(dir, "cycle"))).To(Succeed())
+
+	// resolveSymlinks should not infinite-loop
+	resolved, cleanupDir, err := resolveSymlinks(dir)
+	g.Expect(err).To(BeNil())
+	t.Cleanup(func() { os.RemoveAll(cleanupDir) })
+
+	// The file should be copied
+	content, err := os.ReadFile(filepath.Join(resolved, "file.yaml"))
+	g.Expect(err).To(BeNil())
+	g.Expect(string(content)).To(Equal("data"))
+
+	// The cycle directory should exist but not cause infinite nesting
+	_, err = os.Stat(filepath.Join(resolved, "cycle"))
+	g.Expect(err).To(BeNil())
+
+	// There should NOT be deeply nested cycle/cycle/cycle/... paths
+	_, err = os.Stat(filepath.Join(resolved, "cycle", "cycle", "cycle"))
+	g.Expect(os.IsNotExist(err)).To(BeTrue())
+}