From 1e8a7f68e9c8dea677390b84fa72476ddb4bf1ca Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Tue, 25 Jul 2017 00:33:15 +0300
Subject: [PATCH] Avoid duplicated errors for generic arguments in macro paths

---
 src/librustc_resolve/macros.rs          | 19 ++++++++---
 src/libsyntax/ext/base.rs               |  2 +-
 src/test/ui/span/macro-ty-params.stderr | 44 +------------------------
 3 files changed, 16 insertions(+), 49 deletions(-)

diff --git a/src/librustc_resolve/macros.rs b/src/librustc_resolve/macros.rs
index f8f9b27f148..4d4f6aadce4 100644
--- a/src/librustc_resolve/macros.rs
+++ b/src/librustc_resolve/macros.rs
@@ -385,12 +385,21 @@ impl<'a> Resolver<'a> {
 
     fn resolve_macro_to_def(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
                             -> Result<Def, Determinacy> {
-        let ast::Path { ref segments, span } = *path;
-        segments.iter().find(|segment| segment.parameters.is_some()).map(|segment| {
-            self.session.span_err(segment.parameters.as_ref().unwrap().span(),
-                                  "generic arguments in macro path");
-        });
+        let def = self.resolve_macro_to_def_inner(scope, path, kind, force);
+        if def != Err(Determinacy::Undetermined) {
+            // Do not report duplicated errors on every undetermined resolution.
+            path.segments.iter().find(|segment| segment.parameters.is_some()).map(|segment| {
+                self.session.span_err(segment.parameters.as_ref().unwrap().span(),
+                                      "generic arguments in macro path");
+            });
+        }
+        def
+    }
 
+    fn resolve_macro_to_def_inner(&mut self, scope: Mark, path: &ast::Path,
+                                  kind: MacroKind, force: bool)
+                                  -> Result<Def, Determinacy> {
+        let ast::Path { ref segments, span } = *path;
         let path: Vec<_> = segments.iter().map(|seg| respan(seg.span, seg.identifier)).collect();
         let invocation = self.invocations[&scope];
         self.current_module = invocation.module.get();
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 4881170c1d1..7eeafa72c68 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -608,7 +608,7 @@ pub trait Resolver {
     fn check_unused_macros(&self);
 }
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 pub enum Determinacy {
     Determined,
     Undetermined,
diff --git a/src/test/ui/span/macro-ty-params.stderr b/src/test/ui/span/macro-ty-params.stderr
index ff3847ce1fa..f7115a04826 100644
--- a/src/test/ui/span/macro-ty-params.stderr
+++ b/src/test/ui/span/macro-ty-params.stderr
@@ -16,47 +16,5 @@ error: generic arguments in macro path
 26 |     m!(MyTrait<>);
    |               ^^
 
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:26:15
-   |
-26 |     m!(MyTrait<>);
-   |               ^^
-
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:26:15
-   |
-26 |     m!(MyTrait<>);
-   |               ^^
-
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:22:8
-   |
-22 |     foo::<>!();
-   |        ^^^^
-
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:18:8
-   |
-18 |     foo::<T>!();
-   |        ^^^^^
-
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:18:8
-   |
-18 |     foo::<T>!();
-   |        ^^^^^
-
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:22:8
-   |
-22 |     foo::<>!();
-   |        ^^^^
-
-error: generic arguments in macro path
-  --> $DIR/macro-ty-params.rs:26:15
-   |
-26 |     m!(MyTrait<>);
-   |               ^^
-
-error: aborting due to 10 previous errors
+error: aborting due to 3 previous errors