Fix MethodError printing in case of ambiguity

Author: timholy

base/reflection.jl

@@ -181,11 +181,6 @@ function _methods(f::ANY,t::ANY,lim)
     tt = isa(t,Type) ? Tuple{ft, t.parameters...} : Tuple{ft, t...}
     return _methods_by_ftype(tt, lim)
 end
-function methods_including_ambiguous(f::ANY, t::ANY)
-    ft = isa(f,Type) ? Type{f} : typeof(f)
-    tt = isa(t,Type) ? Tuple{ft, t.parameters...} : Tuple{ft, t...}
-    return ccall(:jl_matching_methods, Any, (Any,Cint,Cint), tt, -1, 1)
-end
 function _methods_by_ftype(t::ANY, lim)
     tp = t.parameters::SimpleVector
     nu = 1
@@ -255,6 +250,13 @@ end
 
 methods(f::Builtin) = MethodList(Method[], typeof(f).name.mt)
 
+function methods_including_ambiguous(f::ANY, t::ANY)
+    ft = isa(f,Type) ? Type{f} : typeof(f)
+    tt = isa(t,Type) ? Tuple{ft, t.parameters...} : Tuple{ft, t...}
+    ms = ccall(:jl_matching_methods, Any, (Any,Cint,Cint), tt, -1, 1)::Array{Any,1}
+    return MethodList(Method[m[3] for m in ms], typeof(f).name.mt)
+end
+
 function methods(f::ANY)
     # return all matches
     return methods(f, Tuple{Vararg{Any}})

test/ambiguous.jl

@@ -43,6 +43,20 @@ end
 callambig(x, y) = ambig(x, y)
 @test_throws MethodError callambig(0x03, 4)
 
+# Printing ambiguity errors
+err = try
+    ambig(0x03, 4)
+catch err
+    err
+end
+io = IOBuffer()
+Base.showerror(io, err)
+lines = split(takebuf_string(io), '\n')
+ambig_checkline(str) = startswith(str, "  ambig(x, y::Integer) at") ||
+                       startswith(str, "  ambig(x::Integer, y) at")
+@test ambig_checkline(lines[2])
+@test ambig_checkline(lines[3])
+
 ## Other ways of accessing functions
 # Test that non-ambiguous cases work
 io = IOBuffer()