cue/load: add tests for issue 3213

Issue #3213 exposed a shortcoming in the modules
logic when there is a Package field explicitly specified
in the cue/load.Config struct. This CL adds some tests
to expose existing behavior in this respect
before a subsequent CL will apply a fix.

For #3213.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: If101f7b6729acdc87a9ae62ebd932044fb276e51
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196177
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

cue/load/loader_test.go

@@ -426,6 +426,46 @@ path:   ""
 module: mod.test/wrong
 root:   ""
 dir:    ""
+display:""`}, {
+		name: "ExplicitPackageWithUnqualifiedImportPath#1",
+		cfg: &Config{
+			Dir:     filepath.Join(testdataDir, "multi"),
+			Package: "main",
+		},
+		args: []string{"."},
+		want: `err:    found packages "main" (file.cue) and "test_package" (file_appengine.cue) in "multi"
+path:   ""
+module: mod.test/test@v0
+root:   $CWD/testdata/testmod
+dir:    ""
+display:""`}, {
+		name: "ExplicitPackageWithUnqualifiedImportPath#2",
+		// This test replicates the failure reported in https://cuelang.org/issue/3213
+		cfg: &Config{
+			Dir:     filepath.Join(testdataDir, "multi2"),
+			Package: "other",
+		},
+		args: []string{"."},
+		want: `err:    mod.test/test/multi2@v0:other: import failed: no dependency found for package "mod.test/test/sub":
+    $CWD/testdata/testmod/multi2/other.cue:3:8
+path:   mod.test/test/multi2@v0:other
+module: mod.test/test@v0
+root:   $CWD/testdata/testmod
+dir:    $CWD/testdata/testmod/multi2
+display:.
+files:
+    $CWD/testdata/testmod/multi2/other.cue`}, {
+		name: "ExplicitPackageWithUnqualifiedImportPath#3",
+		cfg: &Config{
+			Dir:     filepath.Join(testdataDir, "multi3"),
+			Package: "other",
+		},
+		args: []string{"."},
+		want: `err:    found packages "multi3" (multi3.cue) and "other" (other.cue) in "multi3"
+path:   ""
+module: mod.test/test@v0
+root:   $CWD/testdata/testmod
+dir:    ""
 display:""`}}
 	tdtest.Run(t, testCases, func(t *tdtest.T, tc *loadTest) {
 		pkgs := Instances(tc.args, tc.cfg)

cue/load/testdata/testmod/multi2/anon.cue

@@ -0,0 +1 @@
+

cue/load/testdata/testmod/multi2/other.cue

@@ -0,0 +1,7 @@
+package other
+
+import "mod.test/test/sub"
+
+// This is a non-default package for the directory.
+
+x: sub

cue/load/testdata/testmod/multi3/multi3.cue

@@ -0,0 +1,3 @@
+package multi3
+
+// This is the default package for the directory.

cue/load/testdata/testmod/multi3/other.cue

@@ -0,0 +1,7 @@
+package other
+
+import "mod.test/test/sub"
+
+// This is a non-default package for the directory.
+
+x: sub