Align :method Expr return value between interpreter and codegen

Interpreter/inference think the 3-argument `:method` Expr returns `nothing`.
Codegen thinks it returns the new method. I think the latter makes more
sense, because it lets us write explicit syntax-level dependency links
between method definitions and constants (used e.g. for external abstract
interpreters), which is something that Revise may need in the future.
Adjust the interpreter/inference to properly return the method.

Author: Keno

Compiler/src/abstractinterpretation.jl

@@ -3409,7 +3409,7 @@ function abstract_eval_statement_expr(interp::AbstractInterpreter, e::Expr, ssta
     elseif ehead === :cfunction
         return abstract_eval_cfunction(interp, e, sstate, sv)
     elseif ehead === :method
-        rt = (length(e.args) == 1) ? Any : Nothing
+        rt = (length(e.args) == 1) ? Any : Method
         return RTEffects(rt, Any, EFFECTS_UNKNOWN)
     elseif ehead === :copyast
         return abstract_eval_copyast(interp, e, sstate, sv)

src/interpreter.c

@@ -106,9 +106,9 @@ static jl_value_t *eval_methoddef(jl_expr_t *ex, interpreter_state *s)
     }
     atypes = eval_value(args[1], s);
     meth = eval_value(args[2], s);
-    jl_method_def((jl_svec_t*)atypes, mt, (jl_code_info_t*)meth, s->module);
+    jl_method_t *ret = jl_method_def((jl_svec_t*)atypes, mt, (jl_code_info_t*)meth, s->module);
     JL_GC_POP();
-    return jl_nothing;
+    return (jl_value_t *)ret;
 }
 
 // expression evaluator
@@ -626,7 +626,8 @@ static jl_value_t *eval_body(jl_array_t *stmts, interpreter_state *s, size_t ip,
             }
             else if (toplevel) {
                 if (head == jl_method_sym && jl_expr_nargs(stmt) > 1) {
-                    eval_methoddef((jl_expr_t*)stmt, s);
+                    jl_value_t *res = eval_methoddef((jl_expr_t*)stmt, s);
+                    s->locals[jl_source_nslots(s->src) + s->ip] = res;
                 }
                 else if (head == jl_toplevel_sym) {
                     jl_value_t *res = jl_toplevel_eval(s->module, stmt);

test/syntax.jl

@@ -4315,3 +4315,11 @@ module DoubleImport
     import Random
 end
 @test DoubleImport.Random === Test.Random
+
+# Expr(:method) returns the method
+let ex = @Meta.lower function return_my_method(); 1; end
+    code = ex.args[1].code
+    idx = findfirst(ex->Meta.isexpr(ex, :method) && length(ex.args) > 1, code)
+    code[end] = Core.ReturnNode(Core.SSAValue(idx))
+    @test isa(Core.eval(@__MODULE__, ex), Method)
+end