cmd/cue: add more test cases for package resolution

This adds some test cases listed in https://cuelang.org/issue/1138
to make their package resolution semantics explicit in the tests.

For #3155.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I935e91658b84f419e040c7d9ee845944e8b542e9
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1195196
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Chief Cueckoo <chief.cueckoo@gmail.com>

cmd/cue/cmd/testdata/script/pkg_resolution_multiple_packages_build_attr.txtar

@@ -0,0 +1,33 @@
+# Test that a wildcard pattern respects build attributes when determining
+# what packages it resolves to.
+
+exec cue eval ./...
+cmp stdout stdout.golden
+
+! exec cue eval -t something ./...
+stderr '^found packages "x" \(x.cue\) and "y" \(y.cue\) in ".*x"$'
+
+-- stdout.golden --
+x: 5
+// ---
+x: 5
+-- cue.mod/module.cue --
+module: "mod.com"
+language: version: "v0.9.0"
+-- root.cue --
+package root
+
+import "mod.com/x"
+
+x
+-- x/x.cue --
+package x
+
+x: 5
+-- x/y.cue --
+
+@if(something)
+
+package y
+
+y: 5

cmd/cue/cmd/testdata/script/pkg_resolution_multiple_packages_no_matching_path_element.txtar

@@ -0,0 +1,44 @@
+# Test that a relative package path functions the same as an absolute package path
+# when there are no packages in the directory with names that match
+# the final element of the import path.
+
+! exec cue eval root.cue
+# TODO: the error for this isn't quite right: it says:
+#	root.cue: package is root, want x
+# but the evaluation should not care about the package in the root directory
+# because we are not trying to evaluate that package.
+cmp stderr import_stderr.golden
+! exec cue eval mod.com/x
+cmp stderr absolute_stderr.golden
+! exec cue eval ./x
+# TODO: it would be nice if the error output was similar for this case as the others.
+stderr 'found packages "y" \(y.cue\) and "z" \(z.cue\) in ".*"'
+
+-- cue.mod/module.cue --
+module: "mod.com"
+language: version: "v0.9.0"
+-- root.cue --
+package root
+
+import "mod.com/x"
+
+x
+-- x/y.cue --
+package y
+
+y: 5
+-- x/z.cue --
+package z
+
+z: 5
+-- import_stderr.golden --
+import failed: build constraints exclude all CUE files in mod.com/x:
+    root.cue: package is root, want x
+    x/y.cue: package is y, want x
+    x/z.cue: package is z, want x:
+    ./root.cue:3:8
+-- absolute_stderr.golden --
+build constraints exclude all CUE files in mod.com/x:
+    root.cue: package is root, want x
+    x/y.cue: package is y, want x
+    x/z.cue: package is z, want x

cmd/cue/cmd/testdata/script/pkg_resolution_multiple_packages_one_matching_path_element.txtar

@@ -0,0 +1,31 @@
+# Test that a relative package path functions the same as an absolute package path
+# when there are multiple packages in the directory where one has a name
+# that does matches the final element of the import path.
+
+exec cue eval root.cue
+cmp stdout stdout.golden
+exec cue eval mod.com/x
+cmp stdout stdout.golden
+# TODO: the following command fails unexpectedly although it should be consistent with the above.
+! exec cue eval ./x
+stderr 'found packages "x" \(x.cue\) and "y" \(y.cue\) in ".*script-pkg_resolution_multiple_packages_one_matching_path_element.*"'
+
+-- stdout.golden --
+x: 5
+-- cue.mod/module.cue --
+module: "mod.com"
+language: version: "v0.9.0"
+-- root.cue --
+package root
+
+import "mod.com/x"
+
+x
+-- x/x.cue --
+package x
+
+x: 5
+-- x/y.cue --
+package y
+
+y: 5

cmd/cue/cmd/testdata/script/pkg_resolution_path_element_invalid_ident.txtar

@@ -0,0 +1,52 @@
+# Test that a package qualifier is always required to import a package where
+# the final element of the import path is not a valid CUE identifier.
+
+# When there's a qualifier, the import is OK.
+exec cue eval ./test1/root.cue
+cmp stdout stdout.golden
+exec cue eval mod.com/1x:x
+cmp stdout stdout.golden
+exec cue eval ./1x:x
+cmp stdout stdout.golden
+
+# Without a qualifier, it's an error because the chosen package is ambiguous
+# (the package clause in CUE has to declare a valid CUE identifier).
+! exec cue eval ./test2/root.cue
+# Note: the errors here could use improvement. Specifically it says:
+#	package is x, want 1x:
+# but it's not possible for a package to be 1x because it's not a valid CUE identifier.
+cmp stderr test2-import-stderr.golden
+! exec cue eval mod.com/1x
+cmp stderr test2-abs-stderr.golden
+
+# TODO: the following succeeds inappropriately
+exec cue eval ./1x
+
+-- cue.mod/module.cue --
+module: "mod.com"
+language: version: "v0.9.0"
+-- test1/root.cue --
+package test1
+
+import "mod.com/1x:x"
+
+x
+-- test2/root.cue --
+package test1
+
+import "mod.com/1x"
+
+x
+-- 1x/x.cue --
+package x
+
+x: 5
+-- stdout.golden --
+x: 5
+-- test2-import-stderr.golden --
+import failed: build constraints exclude all CUE files in mod.com/1x:
+    1x/x.cue: package is x, want 1x:
+    ./test2/root.cue:3:8
+-- test2-abs-stderr.golden --
+build constraints exclude all CUE files in mod.com/1x:
+    1x/x.cue: package is x, want 1x

cmd/cue/cmd/testdata/script/pkg_resolution_single_package_matching_path_element.txtar

@@ -0,0 +1,26 @@
+# Test that a relative package path functions the same as an absolute package path
+# when there is a single package in the directory with a name
+# that matches the final element of the import path.
+
+exec cue eval root.cue
+cmp stdout output.golden
+exec cue eval mod.com/x
+cmp stdout output.golden
+exec cue eval ./x
+cmp stdout output.golden
+
+-- output.golden --
+x: 5
+-- cue.mod/module.cue --
+module: "mod.com"
+language: version: "v0.9.0"
+-- root.cue --
+package root
+
+import "mod.com/x"
+
+x
+-- x/y.cue --
+package x
+
+x: 5

cmd/cue/cmd/testdata/script/pkg_resolution_single_package_not_matching_path_element.txtar

@@ -0,0 +1,38 @@
+# Test that a relative package path functions the same as an absolute package path
+# when there is a single package in the directory with a name
+# that does not match the final element of the import path.
+
+! exec cue eval root.cue
+# TODO: the error for this isn't quite right: it says:
+#	root.cue: package is root, want x
+# but the evaluation should not care about the package in the root directory
+# because we are not trying to evaluate that package.
+cmp stderr import_stderr.golden
+! exec cue eval mod.com/x
+cmp stderr absolute_stderr.golden
+# TODO: the following command succeeds unexpectedly,
+# although it should be consistent with the above.
+exec cue eval ./x
+
+-- cue.mod/module.cue --
+module: "mod.com"
+language: version: "v0.9.0"
+-- root.cue --
+package root
+
+import "mod.com/x"
+
+x
+-- x/y.cue --
+package y
+
+y: 5
+-- import_stderr.golden --
+import failed: build constraints exclude all CUE files in mod.com/x:
+    root.cue: package is root, want x
+    x/y.cue: package is y, want x:
+    ./root.cue:3:8
+-- absolute_stderr.golden --
+build constraints exclude all CUE files in mod.com/x:
+    root.cue: package is root, want x
+    x/y.cue: package is y, want x