From a367cec6e355a0b17d611acba5577ee72c228971 Mon Sep 17 00:00:00 2001
From: Andy Russell <arussell123@gmail.com>
Date: Mon, 3 Dec 2018 20:45:25 -0500
Subject: [PATCH] emit error with span for empty asserts

Fixes #55547.
---
 src/libsyntax_ext/assert.rs      |  8 ++++++++
 src/test/ui/macros/assert.rs     |  4 ++++
 src/test/ui/macros/assert.stderr | 16 ++++++++++++++++
 3 files changed, 28 insertions(+)
 create mode 100644 src/test/ui/macros/assert.rs
 create mode 100644 src/test/ui/macros/assert.stderr

diff --git a/src/libsyntax_ext/assert.rs b/src/libsyntax_ext/assert.rs
index e3bd2ca01310b..a2384b59048d5 100644
--- a/src/libsyntax_ext/assert.rs
+++ b/src/libsyntax_ext/assert.rs
@@ -24,6 +24,14 @@ pub fn expand_assert<'cx>(
     tts: &[TokenTree],
 ) -> Box<dyn MacResult + 'cx> {
     let mut parser = cx.new_parser_from_tts(tts);
+
+    if parser.token == token::Eof {
+        cx.struct_span_err(sp, "macro requires a boolean expression as an argument")
+            .span_label(sp, "boolean expression required")
+            .emit();
+        return DummyResult::expr(sp);
+    }
+
     let cond_expr = panictry!(parser.parse_expr());
     let custom_msg_args = if parser.eat(&token::Comma) {
         let ts = parser.parse_tokens();
diff --git a/src/test/ui/macros/assert.rs b/src/test/ui/macros/assert.rs
new file mode 100644
index 0000000000000..8732cb58d74a6
--- /dev/null
+++ b/src/test/ui/macros/assert.rs
@@ -0,0 +1,4 @@
+fn main() {
+    assert!();  //~ ERROR requires a boolean expression
+    debug_assert!(); //~ ERROR requires a boolean expression
+}
diff --git a/src/test/ui/macros/assert.stderr b/src/test/ui/macros/assert.stderr
new file mode 100644
index 0000000000000..89faba0cf63dd
--- /dev/null
+++ b/src/test/ui/macros/assert.stderr
@@ -0,0 +1,16 @@
+error: macro requires a boolean expression as an argument
+  --> $DIR/assert.rs:2:5
+   |
+LL |     assert!();  //~ ERROR requires a boolean expression
+   |     ^^^^^^^^^^ boolean expression required
+
+error: macro requires a boolean expression as an argument
+  --> $DIR/assert.rs:3:5
+   |
+LL |     debug_assert!(); //~ ERROR requires a boolean expression
+   |     ^^^^^^^^^^^^^^^^ boolean expression required
+   |
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
+