Fix ICE in suspicious_else_formatting

clippy_lints/src/formatting.rs

@@ -1,5 +1,5 @@
 use crate::utils::{differing_macro_contexts, in_macro, snippet_opt, span_note_and_lint};
-use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
+use rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintPass};
 use rustc::{declare_tool_lint, lint_array};
 use syntax::ast;
 use syntax::ptr::P;
@@ -150,6 +150,7 @@ fn check_else(cx: &EarlyContext<'_>, expr: &ast::Expr) {
         if (is_block(else_) || unsugar_if(else_).is_some())
             && !differing_macro_contexts(then.span, else_.span)
             && !in_macro(then.span)
+            && !in_external_macro(cx.sess, expr.span)
         {
             // workaround for rust-lang/rust#43081
             if expr.span.lo().0 == 0 && expr.span.hi().0 == 0 {

tests/ui/crashes/auxiliary/proc_macro_crash.rs

@@ -0,0 +1,34 @@
+// force-host
+// no-prefer-dynamic
+
+#![feature(repr128)]
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+
+use proc_macro::{Delimiter, Group, Ident, Span, TokenStream, TokenTree};
+use std::iter::FromIterator;
+
+#[proc_macro]
+pub fn macro_test(input_stream: TokenStream) -> TokenStream {
+    let first_token = input_stream.into_iter().next().unwrap();
+    let span = first_token.span();
+
+    TokenStream::from_iter(vec![
+        TokenTree::Ident(Ident::new("fn", Span::call_site())),
+        TokenTree::Ident(Ident::new("code", Span::call_site())),
+        TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
+        TokenTree::Group(Group::new(Delimiter::Brace, {
+            let mut clause = Group::new(Delimiter::Brace, TokenStream::new());
+            clause.set_span(span);
+
+            TokenStream::from_iter(vec![
+                TokenTree::Ident(Ident::new("if", Span::call_site())),
+                TokenTree::Ident(Ident::new("true", Span::call_site())),
+                TokenTree::Group(clause.clone()),
+                TokenTree::Ident(Ident::new("else", Span::call_site())),
+                TokenTree::Group(clause.clone()),
+            ])
+        })),
+    ])
+}

tests/ui/crashes/ice-3741.rs

@@ -0,0 +1,12 @@
+// aux-build:proc_macro_crash.rs
+// run-pass
+
+#![feature(proc_macro_hygiene)]
+#![warn(clippy::suspicious_else_formatting)]
+
+extern crate proc_macro_crash;
+use proc_macro_crash::macro_test;
+
+fn main() {
+    macro_test!(2);
+}