From 0ec6ea7333a8918a96f40110e014f2bbbd72281f Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Sat, 6 Jul 2019 19:45:23 +0300
Subject: [PATCH] resolve: Fix access to extern and stdlib prelude from opaque
 macros

Ok, it's hard to explain what happens, but identifier's hygienic contexts need to be "adjusted" to modules/scopes before they are resolved in them.
To be resolved in all kinds on preludes the identifier needs to be adjusted to the root expansion (aka "no expansion").

Previously this was done for the `macro m() { ::my_crate::foo }` case, but forgotten for all other cases.
---
 src/librustc_resolve/lib.rs                   |  1 +
 src/librustc_resolve/macros.rs                |  1 +
 .../ui/hygiene/auxiliary/stdlib-prelude.rs    |  3 +++
 .../stdlib-prelude-from-opaque-early.rs       | 21 +++++++++++++++++++
 .../stdlib-prelude-from-opaque-late.rs        | 16 ++++++++++++++
 5 files changed, 42 insertions(+)
 create mode 100644 src/test/ui/hygiene/auxiliary/stdlib-prelude.rs
 create mode 100644 src/test/ui/hygiene/stdlib-prelude-from-opaque-early.rs
 create mode 100644 src/test/ui/hygiene/stdlib-prelude-from-opaque-late.rs

diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 795ff3faffa..1216a083700 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -2247,6 +2247,7 @@ impl<'a> Resolver<'a> {
         }
 
         if !module.no_implicit_prelude {
+            ident.span.adjust(Mark::root());
             if ns == TypeNS {
                 if let Some(binding) = self.extern_prelude_get(ident, !record_used) {
                     return Some(LexicalScopeBinding::Item(binding));
diff --git a/src/librustc_resolve/macros.rs b/src/librustc_resolve/macros.rs
index 077c126bdee..7ad54d572f4 100644
--- a/src/librustc_resolve/macros.rs
+++ b/src/librustc_resolve/macros.rs
@@ -856,6 +856,7 @@ impl<'a> Resolver<'a> {
                     match self.hygienic_lexical_parent(module, &mut ident.span) {
                         Some(parent_module) => WhereToResolve::Module(parent_module),
                         None => {
+                            ident.span.adjust(Mark::root());
                             use_prelude = !module.no_implicit_prelude;
                             match ns {
                                 TypeNS => WhereToResolve::ExternPrelude,
diff --git a/src/test/ui/hygiene/auxiliary/stdlib-prelude.rs b/src/test/ui/hygiene/auxiliary/stdlib-prelude.rs
new file mode 100644
index 00000000000..81b0b7faa5b
--- /dev/null
+++ b/src/test/ui/hygiene/auxiliary/stdlib-prelude.rs
@@ -0,0 +1,3 @@
+#![feature(decl_macro)]
+
+pub macro stdlib_macro() {}
diff --git a/src/test/ui/hygiene/stdlib-prelude-from-opaque-early.rs b/src/test/ui/hygiene/stdlib-prelude-from-opaque-early.rs
new file mode 100644
index 00000000000..c8c5c72bf95
--- /dev/null
+++ b/src/test/ui/hygiene/stdlib-prelude-from-opaque-early.rs
@@ -0,0 +1,21 @@
+// check-pass
+// aux-build:stdlib-prelude.rs
+
+#![feature(decl_macro)]
+#![feature(prelude_import)]
+
+extern crate stdlib_prelude;
+
+#[prelude_import]
+use stdlib_prelude::*;
+
+macro mac() {
+    mod m {
+        use std::mem; // OK (extern prelude)
+        stdlib_macro!(); // OK (stdlib prelude)
+    }
+}
+
+mac!();
+
+fn main() {}
diff --git a/src/test/ui/hygiene/stdlib-prelude-from-opaque-late.rs b/src/test/ui/hygiene/stdlib-prelude-from-opaque-late.rs
new file mode 100644
index 00000000000..cf65de2bc23
--- /dev/null
+++ b/src/test/ui/hygiene/stdlib-prelude-from-opaque-late.rs
@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(decl_macro)]
+
+macro mac() {
+    mod m {
+        fn f() {
+            std::mem::drop(0); // OK (extern prelude)
+            drop(0); // OK (stdlib prelude)
+        }
+    }
+}
+
+mac!();
+
+fn main() {}