cue/load: make MultiplePackageError support relative dir paths

cue/errors already knew how to adjust Error.Msg arguments
of type token.Pos so that their filenames are relative.
However, cue/load.MultiplePackageError reported the directory argument
as simply a string, which we cannot safely know is a filename.

Shove the directory name as a token.Position filename,
which ends up working as the line and column numbers are omitted
when left empty. This is mild abuse of the type, hence the note.
However, being able to point to directory "positions" seems useful.

Then teach cue/errors to make both token.Pos and token.Position
argument filenames relative.

Fixes #3703.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I500b343a4f2b2c681a4649d73c3668d09fc2ecf0
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1214888
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cmd/cue/cmd/testdata/script/load_pkg.txtar

@@ -16,7 +16,7 @@ cmp stdout stdout-pkg
 
 # don't allow mixing two differently named packages
 ! exec cue eval kube.cue foo/kube2.cue
-cmpenv stderr different-packages.stderr
+cmp stderr different-packages.stderr
 
 # When passing multiple CUE files in different directories,
 # cue/load will sort the filenames so that children come later.
@@ -35,7 +35,7 @@ cmp stdout stdout-sort
 cd ..
 
 -- different-packages.stderr --
-found packages "kube" (kube.cue) and "kube2" (kube2.cue) in "${WORK@R}"
+found packages "kube" (kube.cue) and "kube2" (kube2.cue) in "."
 -- data.cue --
 foo:3
 -- t.cue --

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

@@ -5,7 +5,7 @@ exec cue eval ./...
 cmp stdout eval-all.golden
 
 ! exec cue eval -t something ./...
-stderr '^found packages "x" \(x.cue\) and "y" \(y.cue\) in ".*x"$'
+stderr '^found packages "x" \(x.cue\) and "y" \(y.cue\) in "x"$'
 
 # Test that a non-wildcard pattern similarly respects
 # build attributes.

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

@@ -8,7 +8,7 @@ cmp stderr import_stderr.golden
 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 ".*"'
+stderr 'found packages "y" \(y.cue\) and "z" \(z.cue\) in "x"'
 
 -- cue.mod/module.cue --
 module: "mod.com"

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

@@ -8,7 +8,7 @@ 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.*"'
+stderr 'found packages "x" \(x.cue\) and "y" \(y.cue\) in "\./x"'
 
 -- stdout.golden --
 x: 5

cue/errors/errors.go

@@ -543,15 +543,21 @@ func writeErr(w io.Writer, err Error, cfg *Config) {
 		// so we make a copy if we need to replace any arguments.
 		didCopy := false
 		for i, arg := range args {
-			if arg, ok := arg.(token.Pos); ok {
-				if !didCopy {
-					args = slices.Clone(args)
-					didCopy = true
-				}
-				pos := arg.Position()
-				pos.Filename = relPath(pos.Filename, cfg)
-				args[i] = pos
+			var pos token.Position
+			switch arg := arg.(type) {
+			case token.Pos:
+				pos = arg.Position()
+			case token.Position:
+				pos = arg
+			default:
+				continue
 			}
+			if !didCopy {
+				args = slices.Clone(args)
+				didCopy = true
+			}
+			pos.Filename = relPath(pos.Filename, cfg)
+			args[i] = pos
 		}
 
 		n, _ := fmt.Fprintf(w, msg, args...)

cue/load/errors.go

@@ -131,7 +131,9 @@ func (e *MultiplePackageError) Msg() (string, []interface{}) {
 		e.Files[0],
 		e.Packages[1],
 		e.Files[1],
-		e.Dir,
+		// To make sure [cue/errors] prints this directory name as relative,
+		// use a [token.Position] even though it's really only meant for regular source files.
+		token.Position{Filename: e.Dir},
 	}
 }