Auto merge of #8297 - Jarcho:if_same_then_else_7579, r=Manishearth

Don't lint `if_same_then_else` with `if let` conditions

fixes #7579

changelog: Don't lint `if_same_then_else` with `if let` conditions

Author: bors

clippy_lints/src/copies.rs

@@ -183,7 +183,7 @@ impl<'tcx> LateLintPass<'tcx> for CopyAndPaste {
                 lint_same_cond(cx, &conds);
                 lint_same_fns_in_if_cond(cx, &conds);
                 // Block duplication
-                lint_same_then_else(cx, &blocks, conds.len() == blocks.len(), expr);
+                lint_same_then_else(cx, &conds, &blocks, conds.len() == blocks.len(), expr);
             }
         }
     }
@@ -192,6 +192,7 @@ impl<'tcx> LateLintPass<'tcx> for CopyAndPaste {
 /// Implementation of `BRANCHES_SHARING_CODE` and `IF_SAME_THEN_ELSE` if the blocks are equal.
 fn lint_same_then_else<'tcx>(
     cx: &LateContext<'tcx>,
+    conds: &[&'tcx Expr<'_>],
     blocks: &[&Block<'tcx>],
     has_conditional_else: bool,
     expr: &'tcx Expr<'_>,
@@ -204,7 +205,7 @@ fn lint_same_then_else<'tcx>(
     // Check if each block has shared code
     let has_expr = blocks[0].expr.is_some();
 
-    let (start_eq, mut end_eq, expr_eq) = if let Some(block_eq) = scan_block_for_eq(cx, blocks) {
+    let (start_eq, mut end_eq, expr_eq) = if let Some(block_eq) = scan_block_for_eq(cx, conds, blocks) {
         (block_eq.start_eq, block_eq.end_eq, block_eq.expr_eq)
     } else {
         return;
@@ -316,14 +317,14 @@ struct BlockEqual {
 
 /// This function can also trigger the `IF_SAME_THEN_ELSE` in which case it'll return `None` to
 /// abort any further processing and avoid duplicate lint triggers.
-fn scan_block_for_eq(cx: &LateContext<'_>, blocks: &[&Block<'_>]) -> Option<BlockEqual> {
+fn scan_block_for_eq(cx: &LateContext<'_>, conds: &[&Expr<'_>], blocks: &[&Block<'_>]) -> Option<BlockEqual> {
     let mut start_eq = usize::MAX;
     let mut end_eq = usize::MAX;
     let mut expr_eq = true;
-    let mut iter = blocks.windows(2);
-    while let Some(&[win0, win1]) = iter.next() {
-        let l_stmts = win0.stmts;
-        let r_stmts = win1.stmts;
+    let mut iter = conds.windows(2).zip(blocks.windows(2));
+    while let Some((&[cond0, cond1], &[block0, block1])) = iter.next() {
+        let l_stmts = block0.stmts;
+        let r_stmts = block1.stmts;
 
         // `SpanlessEq` now keeps track of the locals and is therefore context sensitive clippy#6752.
         // The comparison therefore needs to be done in a way that builds the correct context.
@@ -340,24 +341,26 @@ fn scan_block_for_eq(cx: &LateContext<'_>, blocks: &[&Block<'_>]) -> Option<Bloc
             it1.zip(it2)
                 .fold(0, |acc, (l, r)| if evaluator.eq_stmt(l, r) { acc + 1 } else { 0 })
         };
-        let block_expr_eq = both(&win0.expr, &win1.expr, |l, r| evaluator.eq_expr(l, r));
+        let block_expr_eq = both(&block0.expr, &block1.expr, |l, r| evaluator.eq_expr(l, r));
 
         // IF_SAME_THEN_ELSE
         if_chain! {
             if block_expr_eq;
             if l_stmts.len() == r_stmts.len();
             if l_stmts.len() == current_start_eq;
-            if !is_lint_allowed(cx, IF_SAME_THEN_ELSE, win0.hir_id);
-            if !is_lint_allowed(cx, IF_SAME_THEN_ELSE, win1.hir_id);
+            if !is_lint_allowed(cx, IF_SAME_THEN_ELSE, block0.hir_id);
+            if !is_lint_allowed(cx, IF_SAME_THEN_ELSE, block1.hir_id);
             then {
-                span_lint_and_note(
-                    cx,
-                    IF_SAME_THEN_ELSE,
-                    win0.span,
-                    "this `if` has identical blocks",
-                    Some(win1.span),
-                    "same as this",
-                );
+                if !(matches!(cond0.kind, ExprKind::Let(..)) || !matches!(cond1.kind, ExprKind::Let(..))) {
+                    span_lint_and_note(
+                        cx,
+                        IF_SAME_THEN_ELSE,
+                        block0.span,
+                        "this `if` has identical blocks",
+                        Some(block1.span),
+                        "same as this",
+                    );
+                }
 
                 return None;
             }

tests/ui/if_then_some_else_none.rs

@@ -64,6 +64,23 @@ fn main() {
 
     // Should not issue an error since the `then` block doesn't use `Some` directly.
     let _ = if foo() { into_some("foo") } else { None };
+
+    // Issue #7579
+    let _ = if let Some(0) = None { 0 } else { 0 };
+
+    let _ = if true {
+        0
+    } else if let Some(0) = None {
+        0
+    };
+
+    let _ = if let Some(0) = None {
+        0
+    } else if let None = None {
+        0
+    } else {
+        0
+    };
 }
 
 fn _msrv_1_49() {