Respect namespace in method definitions (#443)

The symbol-lookup in `evaluate_methoddef` was not careful about
avoiding extending methods in Base when the method was unqualified.

Fixes timholy/Revise.jl#579

Author: timholy

src/interpret.jl

@@ -264,13 +264,19 @@ function evaluate_methoddef(frame, node)
     f = node.args[1]
     if isa(f, Symbol)
         mod = moduleof(frame)
-        f = isdefined(mod, f) ? getfield(mod, f) : Core.eval(moduleof(frame), Expr(:function, f))  # create a new function
+        if Base.isbindingresolved(mod, f) && isdefined(mod, f)  # `isdefined` accesses the binding, making it impossible to create a new one
+            f = getfield(mod, f)
+        else
+            f = Core.eval(moduleof(frame), Expr(:function, f))  # create a new function
+        end
+    elseif isa(f, GlobalRef)
+        f = getfield(f.mod, f.name)
     end
     length(node.args) == 1 && return f
     sig = @lookup(frame, node.args[2])::SimpleVector
     body = @lookup(frame, node.args[3])
     ccall(:jl_method_def, Cvoid, (Any, Any, Any), sig, body, moduleof(frame))
-    return nothing
+    return f
 end
 
 function structname(frame, node)

test/toplevel.jl

@@ -235,6 +235,23 @@ module Toplevel end
    @test Toplevel.Testing.Frame === Frame
 end
 
+# Proper handling of namespaces
+# https://github.com/timholy/Revise.jl/issues/579
+module Namespace end
+@testset "Namespace" begin
+    frame = Frame(Namespace, :(sin(::Int) = 10))
+    while true
+        JuliaInterpreter.through_methoddef_or_done!(frame) === nothing && break
+    end
+    @test Namespace.sin(0) == 10
+    if Base.VERSION >= v"1.5"
+        @test Base.sin(0) == 0
+    else
+        @test_broken Base.sin(0) == 0
+        Core.eval(Base, :(sin(x::Int) = sin(float(x))))    # fix the definition of `sin`
+    end
+end
+
 # incremental interpretation solves world-age problems
 # Taken straight from Julia's test/tuple.jl
 module IncTest