Fixes #2426 (if_same_then_else false positive)

clippy_lints/src/copies.rs

@@ -134,15 +134,9 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CopyAndPaste {
 
 /// Implementation of `IF_SAME_THEN_ELSE`.
 fn lint_same_then_else(cx: &LateContext, blocks: &[&Block]) {
-    let hash: &Fn(&&Block) -> u64 = &|block| -> u64 {
-        let mut h = SpanlessHash::new(cx);
-        h.hash_block(block);
-        h.finish()
-    };
-
     let eq: &Fn(&&Block, &&Block) -> bool = &|&lhs, &rhs| -> bool { SpanlessEq::new(cx).eq_block(lhs, rhs) };
 
-    if let Some((i, j)) = search_same(blocks, hash, eq) {
+    if let Some((i, j)) = search_same_sequenced(blocks, eq) {
         span_note_and_lint(
             cx,
             IF_SAME_THEN_ELSE,
@@ -309,6 +303,19 @@ fn bindings<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, pat: &Pat) -> HashMap<Interned
     result
 }
 
+
+fn search_same_sequenced<T, Eq>(exprs: &[T], eq: Eq) -> Option<(&T, &T)>
+where
+    Eq: Fn(&T, &T) -> bool,
+{
+    for win in exprs.windows(2) {
+        if eq(&win[0], &win[1]) {
+            return Some((&win[0], &win[1]));
+        }
+    }
+    None
+}
+
 fn search_same<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Option<(&T, &T)>
 where
     Hash: Fn(&T) -> u64,

tests/run-pass/if_same_then_else.rs

@@ -0,0 +1,13 @@
+#![deny(if_same_then_else)]
+
+fn main() {}
+
+pub fn foo(a: i32, b: i32) -> Option<&'static str> {
+    if a == b {
+        None
+    } else if a > b {
+        Some("a pfeil b")
+    } else {
+        None
+    }
+}

tests/ui/copies.rs

@@ -160,7 +160,7 @@ fn if_same_then_else() -> Result<&'static str, ()> {
     else if false {
         foo();
     }
-    else if foo() { //~ ERROR same body as `if` block
+    else if foo() {
         let _ = match 42 {
             42 => 1,
             a if a > 0 => 2,
@@ -336,7 +336,7 @@ fn if_same_then_else() -> Result<&'static str, ()> {
         let foo = "bar";
         return Ok(&foo[0..]);
     }
-    else { //~ ERROR same body as `if` block
+    else {
         let foo = "";
         return Ok(&foo[0..]);
     }

tests/ui/copies.stderr

@@ -151,32 +151,6 @@ note: same as this
 139 | |     }
     | |_____^
 
-error: this `if` has identical blocks
-   --> $DIR/copies.rs:163:19
-    |
-163 |       else if foo() { //~ ERROR same body as `if` block
-    |  ___________________^
-164 | |         let _ = match 42 {
-165 | |             42 => 1,
-166 | |             a if a > 0 => 2,
-...   |
-169 | |         };
-170 | |     }
-    | |_____^
-    |
-note: same as this
-   --> $DIR/copies.rs:152:13
-    |
-152 |       if true {
-    |  _____________^
-153 | |         let _ = match 42 {
-154 | |             42 => 1,
-155 | |             a if a > 0 => 2,
-...   |
-158 | |         };
-159 | |     }
-    | |_____^
-
 error: this `if` has identical blocks
    --> $DIR/copies.rs:175:10
     |
@@ -370,26 +344,6 @@ note: same as this
 326 | |     }
     | |_____^
 
-error: this `if` has identical blocks
-   --> $DIR/copies.rs:339:10
-    |
-339 |       else { //~ ERROR same body as `if` block
-    |  __________^
-340 | |         let foo = "";
-341 | |         return Ok(&foo[0..]);
-342 | |     }
-    | |_____^
-    |
-note: same as this
-   --> $DIR/copies.rs:331:13
-    |
-331 |       if true {
-    |  _____________^
-332 | |         let foo = "";
-333 | |         return Ok(&foo[0..]);
-334 | |     }
-    | |_____^
-
 error: this `if` has the same condition as a previous if
    --> $DIR/copies.rs:353:13
     |
@@ -427,5 +381,5 @@ note: same as this
 361 |     if 2*a == 1 {
     |        ^^^^^^^^
 
-error: aborting due to 22 previous errors
+error: aborting due to 20 previous errors