From 22e7a6263b457aa6b3402aaebbf98f47da92c03d Mon Sep 17 00:00:00 2001
From: Justus K <justus.k@protonmail.com>
Date: Thu, 9 Jul 2020 13:16:38 +0200
Subject: [PATCH 1/3] Early exit if program doesn't contain a main fn

---
 src/bin/miri.rs | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/bin/miri.rs b/src/bin/miri.rs
index f22f19845c6c..73e52af4ec51 100644
--- a/src/bin/miri.rs
+++ b/src/bin/miri.rs
@@ -5,6 +5,7 @@ extern crate rustc_driver;
 extern crate rustc_hir;
 extern crate rustc_interface;
 extern crate rustc_session;
+extern crate rustc_errors;
 
 use std::convert::TryFrom;
 use std::env;
@@ -13,7 +14,8 @@ use std::str::FromStr;
 use hex::FromHexError;
 use log::debug;
 
-use rustc_session::CtfeBacktrace;
+use rustc_session::{CtfeBacktrace, config::ErrorOutputType};
+use rustc_errors::emitter::{HumanReadableErrorType, ColorConfig};
 use rustc_driver::Compilation;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::ty::TyCtxt;
@@ -32,7 +34,12 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
 
         queries.global_ctxt().unwrap().peek_mut().enter(|tcx| {
             init_late_loggers(tcx);
-            let (entry_def_id, _) = tcx.entry_fn(LOCAL_CRATE).expect("no main function found!");
+            let (entry_def_id, _) = if let Some((entry_def, x)) = tcx.entry_fn(LOCAL_CRATE) {
+                (entry_def, x)
+            } else {
+                let output_ty = ErrorOutputType::HumanReadable(HumanReadableErrorType::Default(ColorConfig::Auto));
+                rustc_session::early_error(output_ty, "miri can only run programs that have a main function");
+            };
             let mut config = self.miri_config.clone();
 
             // Add filename to `miri` arguments.

From c93fc933bd54be1f5237c5411bc70cbc0176cf39 Mon Sep 17 00:00:00 2001
From: Justus K <justus.k@protonmail.com>
Date: Thu, 9 Jul 2020 14:08:45 +0200
Subject: [PATCH 2/3] Add ui test for early exiting if no main

---
 tests/run-pass/no_main.rs     | 1 +
 tests/run-pass/no_main.stderr | 2 ++
 2 files changed, 3 insertions(+)
 create mode 100644 tests/run-pass/no_main.rs
 create mode 100644 tests/run-pass/no_main.stderr

diff --git a/tests/run-pass/no_main.rs b/tests/run-pass/no_main.rs
new file mode 100644
index 000000000000..1ae9a6a35c25
--- /dev/null
+++ b/tests/run-pass/no_main.rs
@@ -0,0 +1 @@
+#![no_main]
diff --git a/tests/run-pass/no_main.stderr b/tests/run-pass/no_main.stderr
new file mode 100644
index 000000000000..52591a8d6da3
--- /dev/null
+++ b/tests/run-pass/no_main.stderr
@@ -0,0 +1,2 @@
+error: miri can only run programs that have a main function
+

From d23e245f38f556e833ca7fc4f616b78e791b923b Mon Sep 17 00:00:00 2001
From: Justus K <justus.k@protonmail.com>
Date: Thu, 9 Jul 2020 17:21:09 +0200
Subject: [PATCH 3/3] Move no_main test to compile-fail

---
 tests/compile-fail/no_main.rs | 2 ++
 tests/run-pass/no_main.rs     | 1 -
 tests/run-pass/no_main.stderr | 2 --
 3 files changed, 2 insertions(+), 3 deletions(-)
 create mode 100644 tests/compile-fail/no_main.rs
 delete mode 100644 tests/run-pass/no_main.rs
 delete mode 100644 tests/run-pass/no_main.stderr

diff --git a/tests/compile-fail/no_main.rs b/tests/compile-fail/no_main.rs
new file mode 100644
index 000000000000..a9e8e816828c
--- /dev/null
+++ b/tests/compile-fail/no_main.rs
@@ -0,0 +1,2 @@
+// error-pattern: miri can only run programs that have a main function
+#![no_main]
diff --git a/tests/run-pass/no_main.rs b/tests/run-pass/no_main.rs
deleted file mode 100644
index 1ae9a6a35c25..000000000000
--- a/tests/run-pass/no_main.rs
+++ /dev/null
@@ -1 +0,0 @@
-#![no_main]
diff --git a/tests/run-pass/no_main.stderr b/tests/run-pass/no_main.stderr
deleted file mode 100644
index 52591a8d6da3..000000000000
--- a/tests/run-pass/no_main.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-error: miri can only run programs that have a main function
-