go/types, types2: panic with cyclic generic type definition

[griesemer]

Compiling

package p

type A[T B[T]] struct{}

type B[T A[T]] = A[T]

leads to a type checkere panic (after CL 711420).

testdata/manual.go:10:6  :  -- checking type A (white, objPath = )
testdata/manual.go:10:11 :  .  -- type B[T]
testdata/manual.go:10:10 :  .  .  -- instantiating type B with [T]
testdata/manual.go:10:10 :  .  .  .  -- type B
testdata/manual.go:12:6  :  .  .  .  .  -- checking type B (white, objPath = A)
testdata/manual.go:12:11 :  .  .  .  .  .  -- type A[T]
testdata/manual.go:12:10 :  .  .  .  .  .  .  -- instantiating type A with [T]
testdata/manual.go:12:10 :  .  .  .  .  .  .  .  -- type A
testdata/manual.go:10:6  :  .  .  .  .  .  .  .  .  ## cycle detected: objPath = A->B->A (len = 2)
testdata/manual.go:10:6  :  .  .  .  .  .  .  .  .  ## cycle contains: generic type in a type parameter list
testdata/manual.go:10:6  :  .  .  .  .  .  .  .  .  => cycle is valid
testdata/manual.go:12:10 :  .  .  .  .  .  .  .  => A[T₁ invalid type] (under = <nil>) // *Named
testdata/manual.go:12:12 :  .  .  .  .  .  .  .  -- type T
testdata/manual.go:12:12 :  .  .  .  .  .  .  .  => T₂ (under = interface{}) // *TypeParam
testdata/manual.go:12:10 :  .  .  .  .  .  .  => A[T₂]
testdata/manual.go:12:11 :  .  .  .  .  .  => A[T₂] (under = <nil>) // *Named
testdata/manual.go:12:19 :  .  .  .  .  .  -- type A[T]
testdata/manual.go:12:18 :  .  .  .  .  .  .  -- instantiating type A with [T]
testdata/manual.go:12:18 :  .  .  .  .  .  .  .  -- type A
testdata/manual.go:10:6  :  .  .  .  .  .  .  .  .  ## cycle detected: objPath = A->B->A (len = 2)
testdata/manual.go:10:6  :  .  .  .  .  .  .  .  .  ## cycle contains: 0 values, 1 type definitions
testdata/manual.go:10:6  :  .  .  .  .  .  .  .  .  => cycle is valid
testdata/manual.go:12:18 :  .  .  .  .  .  .  .  => A[T₁ invalid type] (under = <nil>) // *Named
testdata/manual.go:12:20 :  .  .  .  .  .  .  .  -- type T
testdata/manual.go:12:10 :  .  .  .  .  .  .  .  -- Named.expandUnderlying A[T₂]
testdata/manual.go:12:10 :  .  .  .  .  .  .  .  => A[T₂] (tparams = [], under = <nil>)
testdata/manual.go:12:18 :  .  .  .  .  .  .  => <nil>
testdata/manual.go:12:19 :  .  .  .  .  .  => <nil> // <nil>
testdata/manual.go:12:6  :  .  .  .  .  => type B[T A[T]] = invalid type (black)
testdata/manual.go:10:10 :  .  .  .  => <nil> // <nil>
testdata/manual.go:10:10 :  .  .  => <nil>
testdata/manual.go:10:11 :  .  => <nil> // <nil>
The following panic happened checking types near:
        testdata/manual.go:12:6
        testdata/manual.go:10:6
--- FAIL: TestManual (0.07s)
panic: /Users/gri/goroot/src/cmd/compile/internal/types2/named.go:662: assertion failed [recovered, repanicked]
        panic: nil underlying [recovered, repanicked]

[gabyhelp]

Related Issues

• cmd/compile: panic for cyclic generic interfaces #56045
• go/types: discrepancy in type checking compared to types2 #67436 (closed)
• go/types: recursive type aliases might cause a panic #71284 (closed)
• go/types, types2: cycle to ... panics for a variety of types #74928
• cmd/compile/internal/types2: invalid recursive type not detected and panics #48096 (closed)
• go/types, types2: panic with mutual instantiation #49043 (closed)
• types2, go/types: infinite loop typechecking (invalid) recursive generic struct #48951 (closed)
• go/types: assertion failed error on type declaration cycle #18643 (closed)
• cmd/compile: "panic: assertion failed" when compiling illegal code #47883 (closed)
• go.tools/go/types: cycles not detected for cyclic types used as parameters #7236 (closed)

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