resolve: Prefer macro_rules definitions to in-module macro definitions in some cases

src/test/ui/imports/macros.rs

@@ -45,7 +45,7 @@ mod m3 {
 mod m4 {
     macro_rules! m { () => {} }
     use two_macros::m;
-    m!(); //~ ERROR ambiguous
+    m!();
 }
 
 fn main() {}

src/test/ui/imports/macros.stderr

@@ -1,20 +1,3 @@
-error[E0659]: `m` is ambiguous
-  --> $DIR/macros.rs:48:5
-   |
-LL |     m!(); //~ ERROR ambiguous
-   |     ^ ambiguous name
-   |
-note: `m` could refer to the name defined here
-  --> $DIR/macros.rs:46:5
-   |
-LL |     macro_rules! m { () => {} }
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: `m` could also refer to the name imported here
-  --> $DIR/macros.rs:47:9
-   |
-LL |     use two_macros::m;
-   |         ^^^^^^^^^^^^^
-
 error[E0659]: `m` is ambiguous
   --> $DIR/macros.rs:26:5
    |
@@ -51,6 +34,6 @@ LL |     use two_macros::m;
    |         ^^^^^^^^^^^^^
    = note: macro-expanded macro imports do not shadow
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0659`.

src/test/ui/macros/ambiguity-legacy-vs-modern.rs

@@ -0,0 +1,46 @@
+// Some non-controversial subset of ambiguities "modern macro name" vs "macro_rules"
+// is disambiguated to mitigate regressions from macro modularization.
+// Scoping for `macro_rules` behaves like scoping for `let` at module level, in general.
+
+#![feature(decl_macro)]
+
+fn same_unnamed_mod() {
+    macro m() { 0 }
+
+    macro_rules! m { () => (()) }
+
+    m!() // OK
+}
+
+fn nested_unnamed_mod() {
+    macro m() { 0 }
+
+    {
+        macro_rules! m { () => (()) }
+
+        m!() // OK
+    }
+}
+
+fn nested_unnamed_mod_fail() {
+    macro_rules! m { () => (()) }
+
+    {
+        macro m() { 0 }
+
+        m!() //~ ERROR `m` is ambiguous
+    }
+}
+
+fn nexted_named_mod_fail() {
+    macro m() { 0 }
+
+    #[macro_use]
+    mod inner {
+        macro_rules! m { () => (()) }
+    }
+
+    m!() //~ ERROR `m` is ambiguous
+}
+
+fn main() {}

src/test/ui/macros/ambiguity-legacy-vs-modern.stderr

@@ -0,0 +1,37 @@
+error[E0659]: `m` is ambiguous
+  --> $DIR/ambiguity-legacy-vs-modern.rs:31:9
+   |
+LL |         m!() //~ ERROR `m` is ambiguous
+   |         ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/ambiguity-legacy-vs-modern.rs:26:5
+   |
+LL |     macro_rules! m { () => (()) }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: `m` could also refer to the name defined here
+  --> $DIR/ambiguity-legacy-vs-modern.rs:29:9
+   |
+LL |         macro m() { 0 }
+   |         ^^^^^^^^^^^^^^^
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/ambiguity-legacy-vs-modern.rs:43:5
+   |
+LL |     m!() //~ ERROR `m` is ambiguous
+   |     ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/ambiguity-legacy-vs-modern.rs:40:9
+   |
+LL |         macro_rules! m { () => (()) }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: `m` could also refer to the name defined here
+  --> $DIR/ambiguity-legacy-vs-modern.rs:36:5
+   |
+LL |     macro m() { 0 }
+   |     ^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0659`.