compiler: add regression test for generic methods in interfaces

Add compiler/testdata/go1.27.go, gated behind Go >= 1.27 (the version
that promoted generic methods out of the GenericMethods experiment),
covering both fixes from the previous two commits:

  - genericMethod has a regular method and a generic method (its own
    type parameter); boxing it into an interface must only include the
    regular method in the runtime method set instead of panicking in
    getTypeCodeName.
  - onlyGenericMethod's sole method is generic, so its type code must
    have hasMethodSet == false and no methodSet field at all, not an
    empty one.

Verified this test panics on the pre-fix compiler/interface.go and
passes after it.

compiler/compiler_test.go

@@ -60,6 +60,9 @@ func TestCompiler(t *testing.T) {
 	if goMinor >= 21 {
 		tests = append(tests, testCase{"go1.21.go", "", ""})
 	}
+	if goMinor >= 27 {
+		tests = append(tests, testCase{"go1.27.go", "", ""})
+	}
 
 	for _, tc := range tests {
 		name := tc.file

compiler/testdata/go1.27.go

@@ -0,0 +1,24 @@
+package main
+
+// genericMethod has both a regular method and a "generic method": a method
+// with its own type parameter, independent of any type parameter on the
+// receiver. This is a Go 1.27 feature (see math/rand/v2.Rand.N for a
+// real-world example). Boxing such a value into an interface must not try to
+// encode the generic method's type-parameterized signature into a type code.
+type genericMethod struct{}
+
+func (t genericMethod) Regular(n int) int { return n }
+
+func (t genericMethod) GenericParam[X int | int64](n X) X { return n }
+
+// onlyGenericMethod's only method is generic, so its runtime type must have
+// an empty method set (hasMethodSet must become false, not just numMethods).
+type onlyGenericMethod struct{}
+
+func (t onlyGenericMethod) GenericParam[X int | int64](n X) X { return n }
+
+func useGenericMethods() (any, any) {
+	var g genericMethod
+	var o onlyGenericMethod
+	return any(g), any(o)
+}

compiler/testdata/go1.27.ll

@@ -0,0 +1,67 @@
+; ModuleID = 'go1.27.go'
+source_filename = "go1.27.go"
+target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-i128:128-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-wasi"
+
+%runtime.structField = type { ptr, ptr }
+%runtime._interface = type { ptr, ptr }
+
+@"reflect/types.signature:Regular:func:{basic:int}{basic:int}" = linkonce_odr constant i8 0, align 1
+@"reflect/types.type:named:main.genericMethod" = linkonce_odr constant { ptr, i8, i16, ptr, ptr, ptr, { i32, [1 x ptr] }, [19 x i8] } { ptr @"named:main.genericMethod$methodset", i8 122, i16 -32767, ptr getelementptr ({ ptr, i8, i16, ptr, { i32, [1 x ptr] } }, ptr @"reflect/types.type:pointer:named:main.genericMethod", i32 0, i32 1), ptr @"reflect/types.type:struct:{}", ptr @"reflect/types.type.pkgpath:main", { i32, [1 x ptr] } { i32 1, [1 x ptr] [ptr @"reflect/types.signature:Regular:func:{basic:int}{basic:int}"] }, [19 x i8] c"main.genericMethod\00" }, align 4
+@"reflect/types.type.pkgpath:main" = linkonce_odr unnamed_addr constant [5 x i8] c"main\00", align 1
+@"reflect/types.type:pointer:named:main.genericMethod" = linkonce_odr constant { ptr, i8, i16, ptr, { i32, [1 x ptr] } } { ptr @"pointer:named:main.genericMethod$methodset", i8 -43, i16 -32767, ptr getelementptr ({ ptr, i8, i16, ptr, ptr, ptr, { i32, [1 x ptr] }, [19 x i8] }, ptr @"reflect/types.type:named:main.genericMethod", i32 0, i32 1), { i32, [1 x ptr] } { i32 1, [1 x ptr] [ptr @"reflect/types.signature:Regular:func:{basic:int}{basic:int}"] } }, align 4
+@"reflect/methods.Regular:func:{basic:int}{basic:int}" = linkonce_odr constant i8 0, align 1
+@"main$string" = internal unnamed_addr constant [18 x i8] c"main.genericMethod", align 1
+@"main$string.1" = internal unnamed_addr constant [7 x i8] c"Regular", align 1
+@"pointer:named:main.genericMethod$methodset" = linkonce_odr unnamed_addr constant { i32, [1 x ptr], { ptr } } { i32 1, [1 x ptr] [ptr @"reflect/methods.Regular:func:{basic:int}{basic:int}"], { ptr } { ptr @"(*main.genericMethod).Regular" } }
+@"reflect/types.type:struct:{}" = linkonce_odr constant { i8, i16, ptr, ptr, i32, i16, [0 x %runtime.structField] } { i8 90, i16 0, ptr @"reflect/types.type:pointer:struct:{}", ptr @"reflect/types.type.pkgpath.empty", i32 0, i16 0, [0 x %runtime.structField] zeroinitializer }, align 4
+@"reflect/types.type.pkgpath.empty" = linkonce_odr unnamed_addr constant [1 x i8] zeroinitializer, align 1
+@"reflect/types.type:pointer:struct:{}" = linkonce_odr constant { i8, i16, ptr } { i8 -43, i16 0, ptr @"reflect/types.type:struct:{}" }, align 4
+@"named:main.genericMethod$methodset" = linkonce_odr unnamed_addr constant { i32, [1 x ptr], { ptr } } { i32 1, [1 x ptr] [ptr @"reflect/methods.Regular:func:{basic:int}{basic:int}"], { ptr } { ptr @"(main.genericMethod).Regular$invoke" } }
+@"reflect/types.type:named:main.onlyGenericMethod" = linkonce_odr constant { i8, i16, ptr, ptr, ptr, [23 x i8] } { i8 122, i16 0, ptr @"reflect/types.type:pointer:named:main.onlyGenericMethod", ptr @"reflect/types.type:struct:{}", ptr @"reflect/types.type.pkgpath:main", [23 x i8] c"main.onlyGenericMethod\00" }, align 4
+@"reflect/types.type:pointer:named:main.onlyGenericMethod" = linkonce_odr constant { i8, i16, ptr } { i8 -43, i16 0, ptr @"reflect/types.type:named:main.onlyGenericMethod" }, align 4
+
+declare void @runtime.trackPointer(ptr nocapture readonly, ptr, ptr) #0
+
+; Function Attrs: nounwind
+define hidden void @main.init(ptr %context) unnamed_addr #1 {
+entry:
+  ret void
+}
+
+; Function Attrs: nounwind
+define hidden i32 @"(main.genericMethod).Regular"(i32 %n, ptr %context) unnamed_addr #1 {
+entry:
+  ret i32 %n
+}
+
+; Function Attrs: nounwind
+define hidden { %runtime._interface, %runtime._interface } @main.useGenericMethods(ptr %context) unnamed_addr #1 {
+entry:
+  %stackalloc = alloca i8, align 1
+  call void @runtime.trackPointer(ptr nonnull getelementptr inbounds nuw (i8, ptr @"reflect/types.type:named:main.genericMethod", i32 4), ptr nonnull %stackalloc, ptr undef) #2
+  call void @runtime.trackPointer(ptr null, ptr nonnull %stackalloc, ptr undef) #2
+  call void @runtime.trackPointer(ptr nonnull @"reflect/types.type:named:main.onlyGenericMethod", ptr nonnull %stackalloc, ptr undef) #2
+  call void @runtime.trackPointer(ptr null, ptr nonnull %stackalloc, ptr undef) #2
+  ret { %runtime._interface, %runtime._interface } { %runtime._interface { ptr getelementptr ({ ptr, i8, i16, ptr, ptr, ptr, { i32, [1 x ptr] }, [19 x i8] }, ptr @"reflect/types.type:named:main.genericMethod", i32 0, i32 1), ptr null }, %runtime._interface { ptr @"reflect/types.type:named:main.onlyGenericMethod", ptr null } }
+}
+
+; Function Attrs: nounwind
+define linkonce_odr hidden i32 @"(*main.genericMethod).Regular"(ptr %t, i32 %n, ptr %context) unnamed_addr #1 {
+entry:
+  %stackalloc = alloca i8, align 1
+  call void @runtime.trackPointer(ptr %t, ptr nonnull %stackalloc, ptr undef) #2
+  %0 = call i32 @"(main.genericMethod).Regular"(i32 %n, ptr undef)
+  ret i32 %0
+}
+
+; Function Attrs: nounwind
+define linkonce_odr i32 @"(main.genericMethod).Regular$invoke"(ptr %0, i32 %1, ptr %2) unnamed_addr #1 {
+entry:
+  %ret = call i32 @"(main.genericMethod).Regular"(i32 %1, ptr %2)
+  ret i32 %ret
+}
+
+attributes #0 = { "target-features"="+bulk-memory,+bulk-memory-opt,+call-indirect-overlong,+mutable-globals,+nontrapping-fptoint,+sign-ext,-multivalue,-reference-types" }
+attributes #1 = { nounwind "target-features"="+bulk-memory,+bulk-memory-opt,+call-indirect-overlong,+mutable-globals,+nontrapping-fptoint,+sign-ext,-multivalue,-reference-types" }
+attributes #2 = { nounwind }