cue/interpreter/embed: forbid ** via pkg/path.Match

Our pkg/path.Match func mimics Go's own path.Match in that it can be
used as a validator via `Match(pattern, "")`. This is better than a
`strings.Contains(pattern, "**")` not only because we get consistent
error messages, but also because Contains gives false positives
on valid patterns such as `\**`, which escapes the first star,
or `[x**y]`, where the stars are just part of a character set.

Fix the code, and add more tests that demonstrate that embedding
does support a glob with `\**` now.

This brings embed in line with pkg/path.Match and tool/file.Glob
in terms of what pattern matching syntax and features it supports.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I0ed6fcab9426c6392fb18491a3f656f29c56b41e
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1198692
Reviewed-by: Roger Peppe <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

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

@@ -106,7 +106,7 @@ language: version: "v0.9.0"
     ./test.cue:19:15
 @embed: only relative files are allowed:
     ./test.cue:21:12
-@embed: double star not (yet) supported in glob:
+@embed: invalid glob pattern "**/*.json": '**' is not supported in patterns as of yet:
     ./test.cue:23:15
 @embed: streaming not implemented: found more than one value in file:
     ./test.cue:25:11

cmd/cue/cmd/testdata/script/embed_windows.txtar

@@ -0,0 +1,33 @@
+env CUE_EXPERIMENT=embed
+
+[!windows] cp reuse.json 'star/*.json'
+[!windows] exec cue export --out cue
+[!windows] cmp stdout out/export-unix
+
+[windows] exec cue export --out cue
+[windows] cmp stdout out/export-windows
+
+-- test.cue --
+@extern(embed)
+
+package foo
+
+// Unix OSes can have a file containing a star character, and we can match it.
+// Windows can still use these file paths and glob patterns, but they can't match
+// a file containing a star character, as such filenames are not allowed on Windows.
+
+globStar:       _ @embed(glob="star/*.json")
+globEscapeStar: _ @embed(glob="star/\\**", type=json)
+-- reuse.json --
+{"x": "to be reused for more names"}
+-- star/simple.json --
+{"x": "does not contain a star character"}
+-- out/export-unix --
+globStar: {
+	"star/*.json": x:      "to be reused for more names"
+	"star/simple.json": x: "does not contain a star character"
+}
+globEscapeStar: "star/*.json": x: "to be reused for more names"
+-- out/export-windows --
+globStar: "star/simple.json": x: "does not contain a star character"
+globEscapeStar: {}

cue/interpreter/embed/embed.go

@@ -100,6 +100,7 @@ import (
 	"cuelang.org/go/internal/encoding"
 	"cuelang.org/go/internal/filetypes"
 	"cuelang.org/go/internal/value"
+	pkgpath "cuelang.org/go/pkg/path"
 )
 
 // TODO: obtain a fs.FS from load or something similar
@@ -218,8 +219,10 @@ func (c *compiler) processGlob(glob, scope string, schema adt.Value) (adt.Expr,
 		return nil, ce
 	}
 
-	if strings.Contains(glob, "**") {
-		return nil, errors.Newf(c.pos, "double star not (yet) supported in glob")
+	// Validate that the glob pattern is valid per [pkgpath.Match].
+	// Note that we use Unix match semantics because all embed paths are Unix-like.
+	if _, err := pkgpath.Match(glob, "", pkgpath.Unix); err != nil {
+		return nil, errors.Wrapf(err, c.pos, "invalid glob pattern %q", glob)
 	}
 
 	// If we do not have a type, ensure the extension of the base is fully