feat: allow symlinks in workspaces (#2064)

* e2e-tests: add test for symlinks in workspace

* pkg/build: fix workspace population with files which are symlinks to regular files

This already worked on mac for some reason, which is probably another bug. But it didn't work on linux.

Author: a-crate

e2e-tests/symlinks-in-workspace-build.yaml

@@ -0,0 +1,17 @@
+package:
+  name: symlinks-in-workspace-build
+  description: Test that symlinks are copied into workspaces
+  version: 0.1.0
+  epoch: 0
+
+environment:
+  contents:
+    packages:
+      - busybox
+
+pipeline:
+  - name: Test for symlink presence in workspace
+    runs: |
+      testdata_linked=$(cat testdata-symlink.txt)
+      testdata=$(cat testdata.txt)
+      [ "$testdata" = "$testdata_linked" ]

e2e-tests/test-fixtures/testdata-symlink.txt

@@ -0,0 +1 @@
+testdata.txt

e2e-tests/test-fixtures/testdata.txt

@@ -0,0 +1 @@
+test data is present

pkg/build/build.go

@@ -563,7 +563,25 @@ func (b *Build) populateWorkspace(ctx context.Context, src fs.FS) error {
 
 		mode := fi.Mode()
 		if !mode.IsRegular() {
-			return nil
+			// If this file is a symlink to a regular file, include it.
+			// It would be easier to include all symlinks but that breaks
+			// when the top-level workspace directory is a symlink.
+			if mode&fs.ModeSymlink != 0 {
+				targetPath, err := filepath.EvalSymlinks(filepath.Join(b.SourceDir, path))
+				if err != nil {
+					log.Debugf("path %s eval gives err %v", path, err)
+					return err
+				}
+				target, err := os.Stat(targetPath)
+				if err != nil {
+					return err
+				}
+				if !target.Mode().IsRegular() {
+					return nil
+				}
+			} else {
+				return nil
+			}
 		}
 
 		for _, pat := range ignorePatterns {