cue/interpreter/embed: fix handling of dir matching glob

Currently, the MVP embed implementation sees @embed(glob=dir/*) and
tries to embed dir/subdir. However '*' should only match files, and so
subdir should be skipped.

This CL fixes the implementation.

Per the design in https://cuelang.org/discussion/3264, we will likely
add support for '**' to match 0 or more path elements later. For now the
use of '**' results in an error, but we also update that error message
to indicate that we don't "yet" support '**'.

Fixes #3267.

Signed-off-by: Paul Jolly <[email protected]>
Change-Id: I6e17aaf4e39b1b794951a9e934b7dd47e052ad4c
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1197338
Reviewed-by: Marcel van Lohuizen <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

cmd/cue/cmd/testdata/script/embed.txtar

@@ -23,15 +23,14 @@ b: _ @embed(file="input.yaml")
 
 c: _ @embed(file="test.json", type=text)
 
-d: _ @embed(glob="y/*.*", type=yaml)
+d: _ @embed(glob="y/*", type=yaml)
 
 d: _ @embed(glob="x/*.yaml") // merge into the same map
 
 f: _ @embed(file="openapi.json", type=openapi)
 
 g: _ @embed(file="openapi.json") // test no auto mode!
 
-
 special: {
 	// These are all valid.
 	underscoreFile: _ @embed(file="y/_test.json")
@@ -61,6 +60,8 @@ a1: 2
 { "z": 47 }
 -- .y/test.json --
 { "z": 48 }
+-- y/subdir/another.json --
+{ "z": 49 }
 -- _z/test.json --
 -- x/input.yaml --
 a1: 2

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

@@ -86,15 +86,13 @@ x: 5
     ./test.cue:11:8
 @embed: open y/test.json: no such file or directory:
     ./test.cue:13:13
-@embed: cannot embed directories:
-    ./test.cue:15:8
 @embed: path not normalized, use "x" instead:
     ./test.cue:17:13
 @embed: cannot refer to parent directory:
     ./test.cue:19:15
 @embed: only relative files are allowed:
     ./test.cue:21:12
-@embed: double star not supported in glob:
+@embed: double star not (yet) supported in glob:
     ./test.cue:23:15
 @embed: streaming not implemented: found more than one value in file:
     ./test.cue:25:11

cue/interpreter/embed/embed.go

@@ -139,7 +139,7 @@ type compiler struct {
 
 	// file system cache
 	dir string
-	fs  fs.FS
+	fs  fs.StatFS
 	pos token.Pos
 }
 
@@ -178,7 +178,7 @@ func (c *compiler) Compile(funcName string, scope adt.Value, a *internal.Attr) (
 	// TODO: obtain a fs.FS from load or something similar.
 	dir := filepath.Dir(pos.File().Name())
 	if c.dir != dir {
-		c.fs = os.DirFS(dir)
+		c.fs = os.DirFS(dir).(fs.StatFS) // Documented as implementing fs.StatFS
 		c.dir = dir
 	}
 
@@ -213,7 +213,7 @@ func (c *compiler) processGlob(glob, scope string, schema adt.Value) (adt.Expr,
 	}
 
 	if strings.Contains(glob, "**") {
-		return nil, errors.Newf(c.pos, "double star not supported in glob")
+		return nil, errors.Newf(c.pos, "double star not (yet) supported in glob")
 	}
 
 	m := &adt.StructLit{}
@@ -224,6 +224,15 @@ func (c *compiler) processGlob(glob, scope string, schema adt.Value) (adt.Expr,
 	}
 
 	for _, f := range matches {
+		// TODO: lots of stat calls happening in this MVP so another won't hurt.
+		// We don't support '**' initially, and '*' only matches files, so skip
+		// any directories.
+		if fi, err := c.fs.Stat(f); err != nil {
+			return nil, errors.Newf(c.pos, "failed to stat %s: %v", f, err)
+		} else if fi.IsDir() {
+			continue
+		}
+
 		expr, err := c.decodeFile(f, scope, schema)
 		if err != nil {
 			return nil, err