From 9ed9d6d0d09a690e81841f1fc2e02f16bc9ee2c5 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Sat, 3 Nov 2018 00:07:56 +0300
Subject: [PATCH] resolve: Filter away macro prelude in modules with
 `#[no_implicit_prelude]` on 2018 edition

---
 src/librustc/session/mod.rs                         |  4 ++++
 src/librustc_resolve/macros.rs                      | 12 ++++++++----
 src/test/ui/hygiene/no_implicit_prelude-2018.rs     | 11 +++++++++++
 src/test/ui/hygiene/no_implicit_prelude-2018.stderr | 10 ++++++++++
 src/test/ui/hygiene/no_implicit_prelude.rs          |  5 ++++-
 5 files changed, 37 insertions(+), 5 deletions(-)
 create mode 100644 src/test/ui/hygiene/no_implicit_prelude-2018.rs
 create mode 100644 src/test/ui/hygiene/no_implicit_prelude-2018.stderr

diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index a17825a877d88..d5513080daf5f 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -963,6 +963,10 @@ impl Session {
         self.opts.debugging_opts.teach && self.diagnostic().must_teach(code)
     }
 
+    pub fn rust_2015(&self) -> bool {
+        self.opts.edition == Edition::Edition2015
+    }
+
     /// Are we allowed to use features from the Rust 2018 edition?
     pub fn rust_2018(&self) -> bool {
         self.opts.edition >= Edition::Edition2018
diff --git a/src/librustc_resolve/macros.rs b/src/librustc_resolve/macros.rs
index d5f344346c2d1..83c32a579ccb4 100644
--- a/src/librustc_resolve/macros.rs
+++ b/src/librustc_resolve/macros.rs
@@ -660,10 +660,13 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                     binding.map(|binding| (binding, Flags::MODULE, Flags::empty()))
                 }
                 WhereToResolve::MacroUsePrelude => {
-                    match self.macro_use_prelude.get(&ident.name).cloned() {
-                        Some(binding) => Ok((binding, Flags::PRELUDE, Flags::empty())),
-                        None => Err(Determinacy::Determined),
+                    let mut result = Err(Determinacy::Determined);
+                    if use_prelude || self.session.rust_2015() {
+                        if let Some(binding) = self.macro_use_prelude.get(&ident.name).cloned() {
+                            result = Ok((binding, Flags::PRELUDE, Flags::empty()));
+                        }
                     }
+                    result
                 }
                 WhereToResolve::BuiltinMacros => {
                     match self.builtin_macros.get(&ident.name).cloned() {
@@ -682,7 +685,8 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                     }
                 }
                 WhereToResolve::LegacyPluginHelpers => {
-                    if self.session.plugin_attributes.borrow().iter()
+                    if (use_prelude || self.session.rust_2015()) &&
+                       self.session.plugin_attributes.borrow().iter()
                                                      .any(|(name, _)| ident.name == &**name) {
                         let binding = (Def::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper),
                                        ty::Visibility::Public, ident.span, Mark::root())
diff --git a/src/test/ui/hygiene/no_implicit_prelude-2018.rs b/src/test/ui/hygiene/no_implicit_prelude-2018.rs
new file mode 100644
index 0000000000000..3ad7435fecf29
--- /dev/null
+++ b/src/test/ui/hygiene/no_implicit_prelude-2018.rs
@@ -0,0 +1,11 @@
+// edition:2018
+
+#[no_implicit_prelude]
+mod bar {
+    fn f() {
+        ::std::print!(""); // OK
+        print!(); //~ ERROR cannot find macro `print!` in this scope
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/hygiene/no_implicit_prelude-2018.stderr b/src/test/ui/hygiene/no_implicit_prelude-2018.stderr
new file mode 100644
index 0000000000000..370fc9784ad4d
--- /dev/null
+++ b/src/test/ui/hygiene/no_implicit_prelude-2018.stderr
@@ -0,0 +1,10 @@
+error: cannot find macro `print!` in this scope
+  --> $DIR/no_implicit_prelude-2018.rs:7:9
+   |
+LL |         print!(); //~ ERROR cannot find macro `print!` in this scope
+   |         ^^^^^
+   |
+   = help: have you added the `#[macro_use]` on the module/import?
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/hygiene/no_implicit_prelude.rs b/src/test/ui/hygiene/no_implicit_prelude.rs
index bf07bc05491cc..5b6041945abea 100644
--- a/src/test/ui/hygiene/no_implicit_prelude.rs
+++ b/src/test/ui/hygiene/no_implicit_prelude.rs
@@ -21,7 +21,10 @@ mod bar {
         Vec::new(); //~ ERROR failed to resolve
         ().clone() //~ ERROR no method named `clone` found
     }
-    fn f() { ::foo::m!(); }
+    fn f() {
+        ::foo::m!();
+        println!(); // OK on 2015 edition (at least for now)
+    }
 }
 
 fn main() {}