cue/interpreter/embed: error when embed is not in a module

The embed proposal is designed for CUE files within a module. Standalone
CUE files should not be able to read arbitrary files inside the current
directory unless they are being interpreted in the context of a module.

We also need to fix the `encoding/jsonschema/internal/externaltest`
package because it was using `ModuleRoot` inappropriately. When it's a
relative path, that field is treated relative to `Dir`, but we were
using it as if it were relative to the current directory.

We also need to fix a few tests that were using embedding with
CUE code that wasn't inside a module.

Fixes #3530

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I2f06be29e6a3b15182c1b9c4a849e9e0c35ba0ff
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1203264
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

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

@@ -12,6 +12,10 @@ cmp stdout out/export
 exec cue vet
 cmp stdout out/vet
 
+-- cue.mod/module.cue --
+module: "cue.example"
+language: version: "v0.11.0"
+
 -- test.cue --
 @extern(embed)
 

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

@@ -16,6 +16,10 @@ symlink symlink-dir -> y
 exec cue eval .
 cmp stdout out/std
 
+-- cue.mod/module.cue --
+module: "cue.example"
+language: version: "v0.11.0"
+
 -- test.cue --
 @extern(embed)
 

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

@@ -7,6 +7,10 @@ env CUE_EXPERIMENT=embed
 [windows] exec cue export --out cue
 [windows] cmp stdout out/export-windows
 
+-- cue.mod/module.cue --
+module: "cue.test"
+language: version: "v0.11.0"
+
 -- test.cue --
 @extern(embed)
 

cue/embed_test.go

@@ -16,6 +16,5 @@ func TestEmbedFailsWhenNotInModule(t *testing.T) {
 package foo
 x: _ 	@embed(file="testdata/readme.md",type=text)
 `)
-	qt.Assert(t, qt.IsNil(v.Err()))
-	// TODO qt.Assert(t, qt.ErrorMatches(v.Err(), `xxx`))
+	qt.Assert(t, qt.ErrorMatches(v.Err(), `cannot embed files when not in a module`))
 }

cue/interpreter/embed/embed.go

@@ -125,6 +125,12 @@ func (i *interpreter) Kind() string {
 // NewCompiler returns a compiler that can decode and embed files that exist
 // within a CUE module.
 func (i *interpreter) NewCompiler(b *build.Instance, r *runtime.Runtime) (runtime.Compiler, errors.Error) {
+	if b.Module == "" {
+		return nil, errors.Newf(token.Pos{}, "cannot embed files when not in a module")
+	}
+	if b.Root == "" {
+		return nil, errors.Newf(token.Pos{}, "cannot embed files: no module root found")
+	}
 	return &compiler{
 		b:       b,
 		runtime: (*cue.Context)(r),

encoding/jsonschema/internal/externaltest/tests.go

@@ -93,7 +93,7 @@ func ReadTestDir(dir string) (tests map[string][]*Schema, err error) {
 		Dir: dir,
 		// Just like in the cue/load tests, prevent Go tests from walking up to the root
 		// directory of the git repository, as that almost always causes test cache misses.
-		ModuleRoot: dir,
+		ModuleRoot: ".",
 	})[0]
 	if err := inst.Err; err != nil {
 		return nil, err

encoding/jsonschema/testdata/external/cue.mod/module.cue

@@ -0,0 +1,4 @@
+module: "cue.example"
+language: {
+	version: "v0.11.0"
+}