cue/load: fix loading when Config.Package does not match default package

When a caller of `cue/load.Instances`, specifies an explicit package
to load by setting `Config.Package`, it should be essentially the
same as specifying an explicit package qualifier in all package arguments
that don't already have one. That's not the case currently. This change
fixes that.

Fixes #3213.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I740a16911340e083776303fb0e454b4533e66f2f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196178
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196232
Reviewed-by: Paul Jolly <paul@myitcv.io>

cue/load/instances.go

@@ -58,7 +58,6 @@ func Instances(args []string, c *Config) []*build.Instance {
 	if len(args) == 0 {
 		args = []string{"."}
 	}
-
 	// TODO: This requires packages to be placed before files. At some point this
 	// could be relaxed.
 	i := 0
@@ -75,6 +74,25 @@ func Instances(args []string, c *Config) []*build.Instance {
 			return []*build.Instance{c.newErrInstance(err)}
 		}
 	}
+	if c.Package != "" && c.Package != "_" && c.Package != "*" {
+		// The caller has specified an explicit package to load.
+		// This is essentially the same as passing an explicit package
+		// qualifier to all package arguments that don't already have
+		// one. We add that qualifier here so that there's a distinction
+		// between package paths specified as arguments, which
+		// have the qualifier added, and package paths that are dependencies
+		// of those, which don't.
+		pkgArgs1 := make([]string, 0, len(pkgArgs))
+		for _, p := range pkgArgs {
+			if ip := module.ParseImportPath(p); !ip.ExplicitQualifier {
+				ip.Qualifier = c.Package
+				p = ip.String()
+			}
+			pkgArgs1 = append(pkgArgs1, p)
+		}
+		pkgArgs = pkgArgs1
+	}
+
 	synCache := newSyntaxCache(c)
 	tg := newTagger(c)
 	// Pass all arguments that look like packages to loadPackages

cue/load/loader_test.go

@@ -433,40 +433,44 @@ display:""`}, {
 			Package: "main",
 		},
 		args: []string{"."},
-		want: `err:    found packages "main" (file.cue) and "test_package" (file_appengine.cue) in "multi"
-path:   ""
+		want: `path:   mod.test/test/multi@v0:main
 module: mod.test/test@v0
 root:   $CWD/testdata/testmod
-dir:    ""
-display:""`}, {
+dir:    $CWD/testdata/testmod/multi
+display:.
+files:
+    $CWD/testdata/testmod/multi/file.cue`}, {
 		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
+		want: `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`}, {
+    $CWD/testdata/testmod/multi2/other.cue
+imports:
+    mod.test/test/sub: $CWD/testdata/testmod/sub/sub.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:   ""
+		want: `path:   mod.test/test/multi3@v0:other
 module: mod.test/test@v0
 root:   $CWD/testdata/testmod
-dir:    ""
-display:""`}}
+dir:    $CWD/testdata/testmod/multi3
+display:.
+files:
+    $CWD/testdata/testmod/multi3/other.cue
+imports:
+    mod.test/test/sub: $CWD/testdata/testmod/sub/sub.cue`}}
 	tdtest.Run(t, testCases, func(t *tdtest.T, tc *loadTest) {
 		pkgs := Instances(tc.args, tc.cfg)