cmd/cue: add test cases for embedding files inside symlink dirs

This is different than embedding a symlink itself, as we follow
a symlink as part of traversing a directory to open a regular file
or match a glob resulting in regular files.

For #3299.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I1c02a64a442b2a1c29192a29171b0ad6a903b43e
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1199041
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cmd/cue/cmd/testdata/script/embed_err.txtar

@@ -12,6 +12,7 @@ cmp stderr out/err
 cd symlink
 symlink symlink.json -> test.json
 symlink symlink-parent.json -> ../test.json
+symlink symlink-dir -> y
 exec cue eval .
 cmp stdout out/std
 
@@ -177,8 +178,14 @@ package symlink
 file: _ @embed(file=symlink.json)
 
 glob: _ @embed(glob="*.json")
+
+fileSymlinkDir: _ @embed(file=symlink-dir/test.json)
+
+globSymlinkDir: _ @embed(glob="symlink-dir/*.json")
 -- symlink/test.json --
 { "x": "symlink target file" }
+-- symlink/y/test.json --
+{ "y": "another symlink target file" }
 -- symlink/out/std --
 file: {
     x: "symlink target file"
@@ -194,3 +201,11 @@ glob: {
         x: "symlink target file"
     }
 }
+fileSymlinkDir: {
+    y: "another symlink target file"
+}
+globSymlinkDir: {
+    "symlink-dir/test.json": {
+        y: "another symlink target file"
+    }
+}