cmd/go: make go list error behavior consistent in tests

"go list -test" constructs a package graph, then creates test packages
for the target. If it encounters an error (for example, a syntax error
in a test file or a test function with the wrong signature), it
reports the error and exits without printing the test packages or
their dependencies, even if the -e flag is given. This is a problem
for tools that operate on test files while users are editing them. For
example, autocomplete may not work while the user is typing.

With this change, a new function, load.TestPackagesAndErrors replaces
TestPackagesFor. The new function attaches errors to the returned test
packages instead of returning immediately. "go list -test" calls this
when the -e flag is set. TestPackagesFor now returns the same error as
before, but it returns non-nil packages so that "go list -test"
without -e can print partial results.

Fixes #28491

Change-Id: I141765c4574eae424d872eb9bf7dd63fdfb85efb
Reviewed-on: https://go-review.googlesource.com/c/go/+/164357
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 21 insertions, 24 deletions

diff --git a/src/cmd/go/internal/list/list.go b/src/cmd/go/internal/list/list.go
index e482c393b6..4a6633d9a1 100644
--- a/src/cmd/go/internal/list/list.go
+++ b/src/cmd/go/internal/list/list.go
@@ -447,37 +447,34 @@ func runList(cmd *base.Command, args []string) {
 				continue
 			}
 			if len(p.TestGoFiles)+len(p.XTestGoFiles) > 0 {
-				pmain, ptest, pxtest, err := load.TestPackagesFor(p, nil)
-				if err != nil {
-					if *listE {
-						pkgs = append(pkgs, &load.Package{
-							PackagePublic: load.PackagePublic{
-								ImportPath: p.ImportPath + ".test",
-								Error:      &load.PackageError{Err: err.Error()},
-							},
-						})
-						continue
+				var pmain, ptest, pxtest *load.Package
+				var err error
+				if *listE {
+					pmain, ptest, pxtest = load.TestPackagesAndErrors(p, nil)
+				} else {
+					pmain, ptest, pxtest, err = load.TestPackagesFor(p, nil)
+					if err != nil {
+						base.Errorf("can't load test package: %s", err)
 					}
-					base.Errorf("can't load test package: %s", err)
-					continue
 				}
-				pkgs = append(pkgs, pmain)
-				if ptest != nil {
+				if pmain != nil {
+					pkgs = append(pkgs, pmain)
+					data := *pmain.Internal.TestmainGo
+					h := cache.NewHash("testmain")
+					h.Write([]byte("testmain\n"))
+					h.Write(data)
+					out, _, err := c.Put(h.Sum(), bytes.NewReader(data))
+					if err != nil {
+						base.Fatalf("%s", err)
+					}
+					pmain.GoFiles[0] = c.OutputFile(out)
+				}
+				if ptest != nil && ptest != p {
 					pkgs = append(pkgs, ptest)
 				}
 				if pxtest != nil {
 					pkgs = append(pkgs, pxtest)
 				}
-
-				data := *pmain.Internal.TestmainGo
-				h := cache.NewHash("testmain")
-				h.Write([]byte("testmain\n"))
-				h.Write(data)
-				out, _, err := c.Put(h.Sum(), bytes.NewReader(data))
-				if err != nil {
-					base.Fatalf("%s", err)
-				}
-				pmain.GoFiles[0] = c.OutputFile(out)
 			}
 		}
 	}