From 915db7ae6430baef99f186ba40f08e105b7694fe Mon Sep 17 00:00:00 2001
From: Mazdak Farrokhzad <twingoow@gmail.com>
Date: Thu, 9 Jan 2020 23:00:28 +0100
Subject: [PATCH] expect `fn` after `const unsafe` / `const extern`

---
 src/librustc_parse/parser/item.rs              |  2 +-
 ...onst-extern-fns-dont-need-fn-specifier-2.rs |  7 +++++++
 ...-extern-fns-dont-need-fn-specifier-2.stderr |  8 ++++++++
 ...-const-extern-fns-dont-need-fn-specifier.rs |  8 ++++++++
 ...st-extern-fns-dont-need-fn-specifier.stderr | 18 ++++++++++++++++++
 5 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.rs
 create mode 100644 src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.stderr
 create mode 100644 src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.rs
 create mode 100644 src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.stderr

diff --git a/src/librustc_parse/parser/item.rs b/src/librustc_parse/parser/item.rs
index 918e826fc26bf..866bd1ccb55be 100644
--- a/src/librustc_parse/parser/item.rs
+++ b/src/librustc_parse/parser/item.rs
@@ -140,7 +140,7 @@ impl<'a> Parser<'a> {
                     self.sess.gated_spans.gate(sym::const_extern_fn, lo.to(self.token.span));
                 }
                 let ext = self.parse_extern()?;
-                self.bump(); // `fn`
+                self.expect_keyword(kw::Fn)?;
 
                 let header = FnHeader {
                     unsafety,
diff --git a/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.rs b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.rs
new file mode 100644
index 0000000000000..7ced24808bf6e
--- /dev/null
+++ b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.rs
@@ -0,0 +1,7 @@
+fn main() {}
+
+#[cfg(FALSE)]
+fn container() {
+    const unsafe WhereIsFerris Now() {}
+    //~^ ERROR expected one of `extern` or `fn`
+}
diff --git a/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.stderr b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.stderr
new file mode 100644
index 0000000000000..5ec9e2a91f1dc
--- /dev/null
+++ b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier-2.stderr
@@ -0,0 +1,8 @@
+error: expected one of `extern` or `fn`, found `WhereIsFerris`
+  --> $DIR/issue-68062-const-extern-fns-dont-need-fn-specifier-2.rs:5:18
+   |
+LL |     const unsafe WhereIsFerris Now() {}
+   |                  ^^^^^^^^^^^^^ expected one of `extern` or `fn`
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.rs b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.rs
new file mode 100644
index 0000000000000..1886bfccb4e3e
--- /dev/null
+++ b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.rs
@@ -0,0 +1,8 @@
+fn main() {}
+
+#[cfg(FALSE)]
+fn container() {
+    const extern "Rust" PUT_ANYTHING_YOU_WANT_HERE bug() -> usize { 1 }
+    //~^ ERROR expected `fn`
+    //~| ERROR `const extern fn` definitions are unstable
+}
diff --git a/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.stderr b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.stderr
new file mode 100644
index 0000000000000..cf71ed4d59765
--- /dev/null
+++ b/src/test/ui/consts/const-extern-fn/issue-68062-const-extern-fns-dont-need-fn-specifier.stderr
@@ -0,0 +1,18 @@
+error: expected `fn`, found `PUT_ANYTHING_YOU_WANT_HERE`
+  --> $DIR/issue-68062-const-extern-fns-dont-need-fn-specifier.rs:5:25
+   |
+LL |     const extern "Rust" PUT_ANYTHING_YOU_WANT_HERE bug() -> usize { 1 }
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `fn`
+
+error[E0658]: `const extern fn` definitions are unstable
+  --> $DIR/issue-68062-const-extern-fns-dont-need-fn-specifier.rs:5:5
+   |
+LL |     const extern "Rust" PUT_ANYTHING_YOU_WANT_HERE bug() -> usize { 1 }
+   |     ^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/64926
+   = help: add `#![feature(const_extern_fn)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0658`.