[dev.typeparams] cmd/compile/internal/types2: avoid endless recursion in Comparable...

Use a map to detect recursive types.
With this we can now typecheck fixedbugs/issue8501.go.

Updates #43088.

Change-Id: I7fad6ccf6c94268473ff72b09a3158e13a7f4cc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/276374
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

diff --git a/src/cmd/compile/internal/types2/issues_test.go b/src/cmd/compile/internal/types2/issues_test.go
index 6d39f99424a216eeac90feff3f9b8b5c190cdb06..f33b7c4396ae8398bbd84bb0bedebb07dcb41cb7 100644 (file)
--- a/src/cmd/compile/internal/types2/issues_test.go
+++ b/src/cmd/compile/internal/types2/issues_test.go
@@ -531,3 +531,28 @@ func TestIssue34921(t *testing.T) {
                pkg = res // res is imported by the next package in this test
        }
 }
+
+func TestIssue43088(t *testing.T) {
+       // type T1 struct {
+       //         x T2
+       // }
+       //
+       // type T2 struct {
+       //         x struct {
+       //                 x T2
+       //         }
+       // }
+       n1 := NewTypeName(syntax.Pos{}, nil, "T1", nil)
+       T1 := NewNamed(n1, nil, nil)
+       n2 := NewTypeName(syntax.Pos{}, nil, "T2", nil)
+       T2 := NewNamed(n2, nil, nil)
+       s1 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", T2, false)}, nil)
+       T1.SetUnderlying(s1)
+       s2 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", T2, false)}, nil)
+       s3 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", s2, false)}, nil)
+       T2.SetUnderlying(s3)
+
+       // These calls must terminate (no endless recursion).
+       Comparable(T1)
+       Comparable(T2)
+}

diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index f3a5818b3f962a7d84a37485c68f241a54a61239..048519471cd3442568cd476e878d02f88e91b167 100644 (file)
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -87,6 +87,11 @@ func IsInterface(typ Type) bool {
 
 // Comparable reports whether values of type T are comparable.
 func Comparable(T Type) bool {
+       return comparable(T, nil)
+}
+
+// comparable should only be called by Comparable.
+func comparable(T Type, seen map[Type]bool) bool {
        // If T is a type parameter not constraint by any type
        // list (i.e., it's underlying type is the top type),
        // T is comparable if it has the == method. Otherwise,
@@ -99,6 +104,14 @@ func Comparable(T Type) bool {
                return t.Bound().IsComparable()
        }
 
+       if seen[T] {
+               return true
+       }
+       if seen == nil {
+               seen = make(map[Type]bool)
+       }
+       seen[T] = true
+
        switch t := optype(T.Under()).(type) {
        case *Basic:
                // assume invalid types to be comparable
@@ -108,13 +121,13 @@ func Comparable(T Type) bool {
                return true
        case *Struct:
                for _, f := range t.fields {
-                       if !Comparable(f.typ) {
+                       if !comparable(f.typ, seen) {
                                return false
                        }
                }
                return true
        case *Array:
-               return Comparable(t.elem)
+               return comparable(t.elem, seen)
        case *Sum:
                return t.is(Comparable)
        case *TypeParam:

diff --git a/test/fixedbugs/issue8507.go b/test/fixedbugs/issue8507.go
index ad6ba8ac68b271f79262de47228d83b090620d03..277b3dc7210247812978e6800ed9caf348f6ade6 100644 (file)
--- a/test/fixedbugs/issue8507.go
+++ b/test/fixedbugs/issue8507.go
@@ -9,7 +9,7 @@
 
 package p
 
-type T struct{ T } // ERROR "invalid recursive type T"
+type T struct{ T } // ERROR "invalid recursive type T|cycle"
 
 func f() {
        println(T{} == T{})

diff --git a/test/run.go b/test/run.go
index a3e2ac5e32969570b34b095939d16278a25f9d06..32c74e8210f9d5696456861c21a68f2cd3c16915 100644 (file)
--- a/test/run.go
+++ b/test/run.go
@@ -2130,6 +2130,4 @@ var excluded = map[string]bool{
        "fixedbugs/issue7525e.go":  true,
        "fixedbugs/issue7742.go":   true, // type-checking doesn't terminate
        "fixedbugs/issue7746.go":   true, // type-checking doesn't terminate
-       "fixedbugs/issue8501.go":   true, // crashes
-       "fixedbugs/issue8507.go":   true, // crashes
 }