JuliaLang · JeffBezanson · Aug 14, 2017 · Jul 28, 2017 · Aug 11, 2017 · Aug 11, 2017
diff --git a/Makefile b/Makefile
@@ -218,7 +218,7 @@ define sysimg_builder
 $$(build_private_libdir)/sys$1.o: $$(build_private_libdir)/inference.ji $$(JULIAHOME)/VERSION $$(BASE_SRCS)
 	@$$(call PRINT_JULIA, cd $$(JULIAHOME)/base && \
 	$$(call spawn,$3) $2 -C $$(JULIA_CPU_TARGET) --output-o $$(call cygpath_w,$$@) $$(JULIA_SYSIMG_BUILD_FLAGS) \
-		--startup-file=no --sysimage $$(call cygpath_w,$$<) sysimg.jl $$(RELBUILDROOT) \
+		--startup-file=no --warn-overwrite=yes --sysimage $$(call cygpath_w,$$<) sysimg.jl $$(RELBUILDROOT) \
 		|| { echo '*** This error is usually fixed by running `make clean`. If the error persists$$(COMMA) try `make cleanall`. ***' && false; } )
 .SECONDARY: $(build_private_libdir)/sys$1.o
 endef

diff --git a/NEWS.md b/NEWS.md
@@ -302,6 +302,12 @@ Deprecated or removed
   * `Base.cpad` has been removed; use an appropriate combination of `rpad` and `lpad`
     instead ([#23187]).
 
+Command-line option changes
+---------------------------
+
+  * New option `--warn-overwrite={yes|no}` to control the warning for overwriting method
+    definitions. The default is `no` ([#23002]).
+
 Julia v0.6.0 Release Notes
 ==========================
 

diff --git a/base/loading.jl b/base/loading.jl
@@ -509,7 +509,7 @@ function create_expr_cache(input::String, output::String, concrete_deps::Vector{
         """
     io = open(pipeline(detach(`$(julia_cmd()) -O0
                               --output-ji $output --output-incremental=yes
-                              --startup-file=no --history-file=no
+                              --startup-file=no --history-file=no --warn-overwrite=yes
                               --color=$(have_color ? "yes" : "no")
                               --eval $code_object`), stderr=STDERR),
               "w", STDOUT)

diff --git a/base/options.jl b/base/options.jl
@@ -23,6 +23,7 @@ struct JLOptions
     debug_level::Int8
     check_bounds::Int8
     depwarn::Int8
+    warn_overwrite::Int8
     can_inline::Int8
     polly::Int8
     fast_math::Int8

diff --git a/base/pkg/entry.jl b/base/pkg/entry.jl
@@ -719,6 +719,7 @@ function test!(pkg::AbstractString,
                     --color=$(Base.have_color ? "yes" : "no")
                     --compilecache=$(Bool(Base.JLOptions().use_compilecache) ? "yes" : "no")
                     --check-bounds=yes
+                    --warn-overwrite=yes
                     --startup-file=$(Base.JLOptions().startupfile != 2 ? "yes" : "no")
                     $test_path
                     ```

diff --git a/doc/man/julia.1 b/doc/man/julia.1
@@ -160,6 +160,10 @@ or adhere to declarations in source code
 --depwarn={yes|no|error}
 Enable or disable syntax and method deprecation warnings ('error' turns warnings into errors)
 
+.TP
+--warn-overwrite={yes|no}
+Enable or disable method overwrite warnings
+
 .TP
 --output-o <name>
 Generate an object file (including system image data)

diff --git a/doc/src/manual/getting-started.md b/doc/src/manual/getting-started.md
@@ -127,6 +127,7 @@ julia [switches] -- [programfile] [args...]
  --math-mode={ieee,fast}   Disallow or enable unsafe floating point optimizations (overrides @fastmath declaration)
 
  --depwarn={yes|no|error}  Enable or disable syntax and method deprecation warnings ("error" turns warnings into errors)
+ --warn-overwrite={yes|no} Enable or disable method overwrite warnings
 
  --output-o name           Generate an object file (including system image data)
  --output-ji name          Generate a system image data file (.ji)

diff --git a/src/gf.c b/src/gf.c
@@ -1223,7 +1223,7 @@ static void method_overwrite(jl_typemap_entry_t *newentry, jl_method_t *oldvalue
     jl_method_t *method = (jl_method_t*)newentry->func.method;
     jl_module_t *newmod = method->module;
     jl_module_t *oldmod = oldvalue->module;
-    if (newmod != jl_main_module || oldmod != jl_main_module) {
+    if (jl_options.warn_overwrite == JL_OPTIONS_WARN_OVERWRITE_ON) {
         JL_STREAM *s = JL_STDERR;
         jl_printf(s, "WARNING: Method definition ");
         jl_static_show_func_sig(s, (jl_value_t*)newentry->sig);

diff --git a/src/jloptions.c b/src/jloptions.c
@@ -58,6 +58,7 @@ jl_options_t jl_options = { 0,    // quiet
 #endif
                             JL_OPTIONS_CHECK_BOUNDS_DEFAULT, // check_bounds
                             1,    // deprecation warning
+                            0,    // method overwrite warning
                             1,    // can_inline
                             JL_OPTIONS_POLLY_ON, // polly
                             JL_OPTIONS_FAST_MATH_DEFAULT,
@@ -123,6 +124,7 @@ static const char opts[]  =
 
     // error and warning options
     " --depwarn={yes|no|error}  Enable or disable syntax and method deprecation warnings (\"error\" turns warnings into errors)\n\n"
+    " --warn-overwrite={yes|no} Enable or disable method overwrite warnings"
 
     // compiler output options
     " --output-o name           Generate an object file (including system image data)\n"
@@ -156,6 +158,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
            opt_output_unopt_bc,
            opt_output_bc,
            opt_depwarn,
+           opt_warn_overwrite,
            opt_inline,
            opt_polly,
            opt_math_mode,
@@ -201,6 +204,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
         { "output-ji",       required_argument, 0, opt_output_ji },
         { "output-incremental",required_argument, 0, opt_incremental },
         { "depwarn",         required_argument, 0, opt_depwarn },
+        { "warn-overwrite",  required_argument, 0, opt_warn_overwrite },
         { "inline",          required_argument, 0, opt_inline },
         { "polly",           required_argument, 0, opt_polly },
         { "math-mode",       required_argument, 0, opt_math_mode },
@@ -478,6 +482,14 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
             else
                 jl_errorf("julia: invalid argument to --depwarn={yes|no|error} (%s)", optarg);
             break;
+        case opt_warn_overwrite:
+            if (!strcmp(optarg,"yes"))
+                jl_options.warn_overwrite = JL_OPTIONS_WARN_OVERWRITE_ON;
+            else if (!strcmp(optarg,"no"))
+                jl_options.warn_overwrite = JL_OPTIONS_WARN_OVERWRITE_OFF;
+            else
+                jl_errorf("julia: invalid argument to --warn-overwrite={yes|no|} (%s)", optarg);
+            break;
         case opt_inline:
             if (!strcmp(optarg,"yes"))
                 jl_options.can_inline = 1;

diff --git a/src/julia.h b/src/julia.h
@@ -1692,6 +1692,7 @@ typedef struct {
     int8_t debug_level;
     int8_t check_bounds;
     int8_t depwarn;
+    int8_t warn_overwrite;
     int8_t can_inline;
     int8_t polly;
     int8_t fast_math;
@@ -1752,6 +1753,9 @@ JL_DLLEXPORT int jl_generating_output(void);
 #define JL_OPTIONS_DEPWARN_ON 1
 #define JL_OPTIONS_DEPWARN_ERROR 2
 
+#define JL_OPTIONS_WARN_OVERWRITE_OFF 0
+#define JL_OPTIONS_WARN_OVERWRITE_ON 1
+
 #define JL_OPTIONS_POLLY_ON 1
 #define JL_OPTIONS_POLLY_OFF 0
 

diff --git a/test/cmdlineargs.jl b/test/cmdlineargs.jl
@@ -429,3 +429,30 @@ for precomp in ("yes", "no")
     @test length(lno.captures) == 1
     @test parse(Int, lno.captures[1]) > 0
 end
+
+# PR #23002
+let exename = `$(Base.julia_cmd()) --startup-file=no`
+    for (mac, flag, pfix, msg) in [("@test_nowarn", ``, "_1", ""),
+                                   ("@test_warn",   `--warn-overwrite=yes`, "_2", "\"WARNING: Method definition\"")]
+        str = """
+        using Base.Test
+        try
+            # issue #18725
+            $mac $msg @eval Main begin
+                f18725$(pfix)(x) = 1
+                f18725$(pfix)(x) = 2
+            end
+            @test Main.f18725$(pfix)(0) == 2
+            # PR #23030
+            $mac $msg @eval Main module Module23030$(pfix)
+                f23030$(pfix)(x) = 1
+                f23030$(pfix)(x) = 2
+            end
+        catch
+            exit(-1)
+        end
+        exit(0)
+        """
+        run(`$exename $flag -e $str`)
+    end
+end
diff --git a/test/core.jl b/test/core.jl
@@ -4680,17 +4680,6 @@ end
 @test f14893() == 14893
 @test M14893.f14893() == 14893
 
-# issue #18725
-@test_nowarn @eval Main begin
-    f18725(x) = 1
-    f18725(x) = 2
-end
-@test Main.f18725(0) == 2
-@test_warn "WARNING: Method definition f18725(Any) in module Module18725" @eval Main module Module18725
-    f18725(x) = 1
-    f18725(x) = 2
-end
-
 # issue #19599
 f19599(x::((S)->Vector{S})(T)...) where {T} = 1
 @test f19599([1],[1]) == 1

diff --git a/test/misc.jl b/test/misc.jl
@@ -239,7 +239,7 @@ let
     redir_err = "redirect_stderr(STDOUT)"
     exename = Base.julia_cmd()
     script = "$redir_err; module A; f() = 1; end; A.f() = 1"
-    warning_str = read(`$exename --startup-file=no -e $script`, String)
+    warning_str = read(`$exename --warn-overwrite=yes --startup-file=no -e $script`, String)
     @test contains(warning_str, "f()")
 end