From 51cf0d1be718469cbf48ee97d4b17ab6d0e26ee5 Mon Sep 17 00:00:00 2001
From: Mark McCaskey <mark@wasmer.io>
Date: Mon, 22 Apr 2019 16:03:04 -0700
Subject: [PATCH 1/3] reduce suggested backends to the ones compiled into
 wasmer

---
 src/bin/wasmer.rs | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/bin/wasmer.rs b/src/bin/wasmer.rs
index b9606a225a7..4b190893317 100644
--- a/src/bin/wasmer.rs
+++ b/src/bin/wasmer.rs
@@ -105,7 +105,22 @@ enum Backend {
 
 impl Backend {
     pub fn variants() -> &'static [&'static str] {
-        &["singlepass", "cranelift", "llvm"]
+        #[cfg(all(feature = "backend:singlepass", feature = "backend:llvm"))]
+        {
+            &["cranelift", "singlepass", "llvm"]
+        }
+        #[cfg(all(not(feature = "backend:singlepass"), feature = "backend:llvm"))]
+        {
+            &["cranelift", "llvm"]
+        }
+        #[cfg(all(feature = "backend:singlepass", not(feature = "backend:llvm")))]
+        {
+            &["cranelift", "singlepass"]
+        }
+        #[cfg(all(not(feature = "backend:singlepass"), not(feature = "backend:llvm")))]
+        {
+            &["cranelift"]
+        }
     }
 }
 

From 015bf7895374222d6cd39b51218cf6f1f77980d7 Mon Sep 17 00:00:00 2001
From: Mark McCaskey <mark@wasmer.io>
Date: Mon, 22 Apr 2019 16:06:22 -0700
Subject: [PATCH 2/3] update changelog

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a96a09994e..e66436c7269 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ All PRs to the Wasmer repository must add to this file.
 Blocks of changes will separated by version increments.
 
 ## **[Unreleased]**
+- [#382](https://github.com/wasmerio/wasmer/pull/382) Improve error message on `--backend` flag to only suggest currently enabled backends
 - [#379](https://github.com/wasmerio/wasmer/pull/379) Fix small return types from imported functions.
 - [#371](https://github.com/wasmerio/wasmer/pull/371) Add more Debug impl for WASI types
 - [#368](https://github.com/wasmerio/wasmer/pull/368) Fix issue with write buffering

From e8b2660eb7ddcd89fa3d517ed68d9c5479eff3a9 Mon Sep 17 00:00:00 2001
From: Mark McCaskey <mark@wasmer.io>
Date: Mon, 22 Apr 2019 16:14:12 -0700
Subject: [PATCH 3/3] greatly simplify logic -- thanks Lachlan!

---
 src/bin/wasmer.rs | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/src/bin/wasmer.rs b/src/bin/wasmer.rs
index 4b190893317..4ab0120451a 100644
--- a/src/bin/wasmer.rs
+++ b/src/bin/wasmer.rs
@@ -105,22 +105,13 @@ enum Backend {
 
 impl Backend {
     pub fn variants() -> &'static [&'static str] {
-        #[cfg(all(feature = "backend:singlepass", feature = "backend:llvm"))]
-        {
-            &["cranelift", "singlepass", "llvm"]
-        }
-        #[cfg(all(not(feature = "backend:singlepass"), feature = "backend:llvm"))]
-        {
-            &["cranelift", "llvm"]
-        }
-        #[cfg(all(feature = "backend:singlepass", not(feature = "backend:llvm")))]
-        {
-            &["cranelift", "singlepass"]
-        }
-        #[cfg(all(not(feature = "backend:singlepass"), not(feature = "backend:llvm")))]
-        {
-            &["cranelift"]
-        }
+        &[
+            "cranelift",
+            #[cfg(feature = "backend:singlepass")]
+            "singlepass",
+            #[cfg(feature = "backend:llvm")]
+            "llvm",
+        ]
     }
 }