[release-branch.go1.11] go/types: avoid certain problems with recursive alias type...

It is possible to create certain recursive type declarations involving
alias types which cause the type-checker to produce an (invalid) type
for the alias because it is not yet available. By type-checking alias
declarations in a 2nd phase, the problem is mitigated a bit since it
requires more convoluted alias declarations for the problem to appear.

Also re-enable testing of fixedbugs/issue27232.go again (which was the
original cause for this change).

Updates #28576.
Fixes #28972.

Change-Id: If6f9656a95262e6575b01c4a003094d41551564b
Reviewed-on: https://go-review.googlesource.com/c/147597
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-on: https://go-review.googlesource.com/c/151500
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>

diff --git a/src/go/types/resolver.go b/src/go/types/resolver.go
index 5cbaba187b964b4b56d6424de63adeaf068ad666..6646711e7fa4d99cc437fd356d1a52abb56a7647 100644 (file)
--- a/src/go/types/resolver.go
+++ b/src/go/types/resolver.go
@@ -538,7 +538,25 @@ func (check *Checker) packageObjects() {
        // pre-allocate space for type declaration paths so that the underlying array is reused
        typePath := make([]*TypeName, 0, 8)
 
+       // We process non-alias declarations first, in order to avoid situations where
+       // the type of an alias declaration is needed before it is available. In general
+       // this is still not enough, as it is possible to create sufficiently convoluted
+       // recursive type definitions that will cause a type alias to be needed before it
+       // is available (see issue #25838 for examples).
+       // As an aside, the cmd/compiler suffers from the same problem (#25838).
+       var aliasList []*TypeName
+       // phase 1
        for _, obj := range objList {
+               // If we have a type alias, collect it for the 2nd phase.
+               if tname, _ := obj.(*TypeName); tname != nil && check.objMap[tname].alias {
+                       aliasList = append(aliasList, tname)
+                       continue
+               }
+
+               check.objDecl(obj, nil, typePath)
+       }
+       // phase 2
+       for _, obj := range aliasList {
                check.objDecl(obj, nil, typePath)
        }