From 97833204f8f2b9cf84fd2785bbc8c6114acfa06d Mon Sep 17 00:00:00 2001
From: Paul Scheduikat <lu4p@pm.me>
Date: Sun, 19 Jan 2025 03:52:35 +0100
Subject: [PATCH] skip all type parameters in recordType

We only did this for Container in the type switch, but not for Struct.
The added test case panics otherwise.
Just like in the previous case, we still don't need to recurse
into type parameters for fieldToStruct to be filled correctly.

Fixes #899
---
 main.go                          | 20 +++++++++++---------
 testdata/script/typeparams.txtar |  8 ++++++--
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/main.go b/main.go
index a321208..00eea79 100644
--- a/main.go
+++ b/main.go
@@ -1683,21 +1683,23 @@ func computeFieldToStruct(info *types.Info) map[*types.Var]*types.Struct {
 // Since types can be recursive, we need a map to avoid cycles.
 // We only need to track named types as done, as all cycles must use them.
 func recordType(used, origin types.Type, done map[*types.Named]bool, fieldToStruct map[*types.Var]*types.Struct) {
+	used = types.Unalias(used)
 	if origin == nil {
 		origin = used
-	}
-	origin = types.Unalias(origin)
-	used = types.Unalias(used)
-	type Container interface{ Elem() types.Type }
-	switch used := used.(type) {
-	case Container:
-		// origin may be a *types.TypeParam, which is not a Container.
+	} else {
+		origin = types.Unalias(origin)
+		// origin may be a [*types.TypeParam].
 		// For now, we haven't found a need to recurse in that case.
 		// We can edit this code in the future if we find an example,
 		// because we panic if a field is not in fieldToStruct.
-		if origin, ok := origin.(Container); ok {
-			recordType(used.Elem(), origin.Elem(), done, fieldToStruct)
+		if _, ok := origin.(*types.TypeParam); ok {
+			return
 		}
+	}
+	type Container interface{ Elem() types.Type }
+	switch used := used.(type) {
+	case Container:
+		recordType(used.Elem(), origin.(Container).Elem(), done, fieldToStruct)
 	case *types.Named:
 		if done[used] {
 			return
diff --git a/testdata/script/typeparams.txtar b/testdata/script/typeparams.txtar
index cb17824..0c6156a 100644
--- a/testdata/script/typeparams.txtar
+++ b/testdata/script/typeparams.txtar
@@ -24,7 +24,7 @@ type GenericVector[GenericParamT any] []GenericParamT
 
 type GenericGraph[T any] struct {
 	Content T
-	Edges []GenericGraph[T]
+	Edges   []GenericGraph[T]
 }
 
 type PredeclaredSignedInteger interface {
@@ -40,7 +40,7 @@ type StringableSignedInteger interface {
 type CombineEmbeds interface {
 	string | int
 
-	interface { EmbeddedMethod() }
+	interface{ EmbeddedMethod() }
 	RegularMethod()
 }
 
@@ -49,3 +49,7 @@ type Slice[T any] []T
 func sliceOfPointer() Slice[*any] {
 	return []*any{}
 }
+
+type Map[K, V comparable] map[K]V
+
+var _ = Map[string, struct{}]{}