Merge pull request #21278 from JuliaLang/jb/fix20614

fix #20614, need error for `Vararg` on non-final argument

Author: JeffBezanson

src/method.c

@@ -668,6 +668,12 @@ JL_DLLEXPORT void jl_method_def(jl_svec_t *argdata,
                               jl_symbol_name(m->file),
                               m->line);
         }
+        if (jl_is_vararg_type(elt) && i < na-1)
+            jl_exceptionf(jl_argumenterror_type,
+                          "Vararg on non-final argument in method definition for %s at %s:%d",
+                          jl_symbol_name(name),
+                          jl_symbol_name(m->file),
+                          m->line);
     }
 
     int ishidden = !!strchr(jl_symbol_name(name), '#');

test/parse.jl

@@ -695,6 +695,11 @@ let m_error, error_out, filename = Base.source_path()
     m_error = try @eval method_c6(A; B) = 3; catch e; e; end
     error_out = sprint(showerror, m_error)
     @test error_out == "syntax: keyword argument \"B\" needs a default value"
+
+    # issue #20614
+    m_error = try @eval foo{N}(types::NTuple{N}, values::Vararg{Any,N}, c) = nothing; catch e; e; end
+    error_out = sprint(showerror, m_error)
+    @test startswith(error_out, "ArgumentError: Vararg on non-final argument")
 end
 
 # issue #7272