go/types: don't update package-external types when checking validity

The recently added type-validity check uses a new field of Named
types for marking (to detect cycles). That field was modified even
if the type was not part of the current package or belonged to the
Universe scope (error type). This led to race conditions if the
package's type was imported by multiple, concurrently type-checked
packages.

A test would be nice but it's a bit cumbersome to set one up.
Verified manually that package-external types are left alone.

Fixes #35049.

Change-Id: I51686bef47fcca48b99b91ecb1b2e9d58e135ea6
Reviewed-on: https://go-review.googlesource.com/c/go/+/202483
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 83d40939a87a91cb1eda8c91c30834002107e809..5c0e611c519eb36b29d64d2aa2cff95bc5ae70ac 100644 (file)
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -311,19 +311,29 @@ func (check *Checker) validType(typ Type, path []Object) typeInfo {
                }
 
        case *Named:
+               // don't touch the type if it is from a different package or the Universe scope
+               // (doing so would lead to a race condition - was issue #35049)
+               if t.obj.pkg != check.pkg {
+                       return valid
+               }
+
                // don't report a 2nd error if we already know the type is invalid
                // (e.g., if a cycle was detected earlier, via Checker.underlying).
                if t.underlying == Typ[Invalid] {
                        t.info = invalid
                        return invalid
                }
+
                switch t.info {
                case unknown:
                        t.info = marked
-                       t.info = check.validType(t.orig, append(path, t.obj))
+                       t.info = check.validType(t.orig, append(path, t.obj)) // only types of current package added to path
                case marked:
                        // cycle detected
                        for i, tn := range path {
+                               if t.obj.pkg != check.pkg {
+                                       panic("internal error: type cycle via package-external type")
+                               }
                                if tn == t.obj {
                                        check.cycleError(path[i:])
                                        t.info = invalid