Fix false positive for ifs_same_cond and cfg!

Author: mcarton

Diff for: src/utils/hir.rs

@@ -4,6 +4,7 @@ use rustc_front::hir::*;
 use std::hash::{Hash, Hasher, SipHasher};
 use syntax::ast::Name;
 use syntax::ptr::P;
+use utils::differing_macro_contexts;
 
 /// Type used to check whether two ast are the same. This is different from the operator
 /// `==` on ast types as this operator would compare true equality with ID and span.
@@ -53,6 +54,10 @@ impl<'a, 'tcx: 'a> SpanlessEq<'a, 'tcx> {
     // ok, it’s a big function, but mostly one big match with simples cases
     #[allow(cyclomatic_complexity)]
     pub fn eq_expr(&self, left: &Expr, right: &Expr) -> bool {
+        if self.ignore_fn && differing_macro_contexts(left.span, right.span) {
+            return false;
+        }
+
         if let (Some(l), Some(r)) = (constant(self.cx, left), constant(self.cx, right)) {
             if l == r {
                 return true;

Diff for: tests/compile-fail/copies.rs

@@ -12,7 +12,7 @@ fn foo() -> bool { unimplemented!() }
 
 #[deny(if_same_then_else)]
 #[deny(match_same_arms)]
-fn if_same_then_else() -> &'static str {
+fn if_same_then_else() -> Result<&'static str, ()> {
     if true {
         foo();
     }
@@ -129,17 +129,24 @@ fn if_same_then_else() -> &'static str {
         _ => (),
     }
 
+    if true {
+        try!(Ok("foo"));
+    }
+    else { //~ERROR this `if` has identical blocks
+        try!(Ok("foo"));
+    }
+
     if true {
         let foo = "";
-        return &foo[0..];
+        return Ok(&foo[0..]);
     }
     else if false {
         let foo = "bar";
-        return &foo[0..];
+        return Ok(&foo[0..]);
     }
     else { //~ERROR this `if` has identical blocks
         let foo = "";
-        return &foo[0..];
+        return Ok(&foo[0..]);
     }
 }
 
@@ -168,6 +175,15 @@ fn ifs_same_cond() {
     else if a == 1 {
     }
 
+    // See #659
+    if cfg!(feature = "feature1-659") {
+        1
+    } else if cfg!(feature = "feature2-659") {
+        2
+    } else {
+        3
+    };
+
     let mut v = vec![1];
     if v.pop() == None { // ok, functions
     }