Fix branches_sharing_code suggests wrongly when dealing with macros (#14907)

Closes rust-lang/rust-clippy#14873

changelog: [`branches_sharing_code`] fix wrong suggestions when dealing
with macros

Author: dswij

clippy_lints/src/copies.rs

@@ -425,7 +425,9 @@ fn scan_block_for_eq<'tcx>(
             modifies_any_local(cx, stmt, &cond_locals)
                 || !eq_stmts(stmt, blocks, |b| b.stmts.get(i), &mut eq, &mut moved_locals)
         })
-        .map_or(block.stmts.len(), |(i, _)| i);
+        .map_or(block.stmts.len(), |(i, stmt)| {
+            adjust_by_closest_callsite(i, stmt, block.stmts[..i].iter().enumerate().rev())
+        });
 
     if local_needs_ordered_drop {
         return BlockEq {
@@ -467,7 +469,9 @@ fn scan_block_for_eq<'tcx>(
                     .is_none_or(|s| hash != hash_stmt(cx, s))
             })
         })
-        .map_or(block.stmts.len() - start_end_eq, |(i, _)| i);
+        .map_or(block.stmts.len() - start_end_eq, |(i, stmt)| {
+            adjust_by_closest_callsite(i, stmt, (0..i).rev().zip(block.stmts[(block.stmts.len() - i)..].iter()))
+        });
 
     let moved_locals_at_start = moved_locals.len();
     let mut i = end_search_start;
@@ -522,6 +526,49 @@ fn scan_block_for_eq<'tcx>(
     }
 }
 
+/// Adjusts the index for which the statements begin to differ to the closest macro callsite. This
+/// avoids giving suggestions that requires splitting a macro call in half, when only a part of the
+/// macro expansion is equal.
+///
+/// For example, for the following macro:
+/// ```rust,ignore
+/// macro_rules! foo {
+///    ($x:expr) => {
+///        let y = 42;
+///        $x;
+///    };
+/// }
+/// ```
+/// If the macro is called like this:
+/// ```rust,ignore
+/// if false {
+///    let z = 42;
+///    foo!(println!("Hello"));
+/// } else {
+///    let z = 42;
+///    foo!(println!("World"));
+/// }
+/// ```
+/// Although the expanded `let y = 42;` is equal, the macro call should not be included in the
+/// suggestion.
+fn adjust_by_closest_callsite<'tcx>(
+    i: usize,
+    stmt: &'tcx Stmt<'tcx>,
+    mut iter: impl Iterator<Item = (usize, &'tcx Stmt<'tcx>)>,
+) -> usize {
+    let Some((_, first)) = iter.next() else {
+        return 0;
+    };
+
+    // If it is already at the boundary of a macro call, then just return.
+    if first.span.source_callsite() != stmt.span.source_callsite() {
+        return i;
+    }
+
+    iter.find(|(_, stmt)| stmt.span.source_callsite() != first.span.source_callsite())
+        .map_or(0, |(i, _)| i + 1)
+}
+
 fn check_for_warn_of_moved_symbol(cx: &LateContext<'_>, symbols: &[(HirId, Symbol)], if_expr: &Expr<'_>) -> bool {
     get_enclosing_block(cx, if_expr.hir_id).is_some_and(|block| {
         let ignore_span = block.span.shrink_to_lo().to(if_expr.span);

tests/ui/branches_sharing_code/shared_at_bottom.rs

@@ -239,3 +239,40 @@ fn fp_if_let_issue7054() {
 }
 
 fn main() {}
+
+mod issue14873 {
+    fn foo() -> i32 {
+        todo!()
+    }
+
+    macro_rules! qux {
+        ($a:ident, $b:ident, $condition:expr) => {
+            if $condition {
+                "."
+            } else {
+                ""
+            };
+            $a = foo();
+            $b = foo();
+        };
+    }
+
+    fn share_on_bottom() {
+        let mut a = 0;
+        let mut b = 0;
+        if false {
+            qux!(a, b, a == b);
+        } else {
+            qux!(a, b, a != b);
+        };
+
+        if false {
+            qux!(a, b, a == b);
+            let y = 1;
+        } else {
+            qux!(a, b, a != b);
+            let y = 1;
+            //~^ branches_sharing_code
+        }
+    }
+}

tests/ui/branches_sharing_code/shared_at_bottom.stderr

@@ -157,5 +157,20 @@ LL ~     if x == 17 { b = 1; a = 0x99; } else { }
 LL +     a = 0x99;
    |
 
-error: aborting due to 9 previous errors
+error: all if blocks contain the same code at the end
+  --> tests/ui/branches_sharing_code/shared_at_bottom.rs:274:9
+   |
+LL | /             let y = 1;
+LL | |
+LL | |         }
+   | |_________^
+   |
+   = warning: some moved values might need to be renamed to avoid wrong references
+help: consider moving these statements after the if
+   |
+LL ~         }
+LL +         let y = 1;
+   |
+
+error: aborting due to 10 previous errors
 

tests/ui/branches_sharing_code/shared_at_top.rs

@@ -124,3 +124,34 @@ fn pf_local_with_inferred_type_issue7053() {
 }
 
 fn main() {}
+
+mod issue14873 {
+    fn foo() -> i32 {
+        todo!()
+    }
+
+    macro_rules! qux {
+        ($a:ident, $b:ident, $condition:expr) => {
+            let $a: i32 = foo();
+            let $b: i32 = foo();
+            if $condition { "." } else { "" }
+        };
+    }
+
+    fn share_on_top() {
+        if false {
+            qux!(a, b, a == b);
+        } else {
+            qux!(a, b, a != b);
+        };
+
+        if false {
+            //~^ branches_sharing_code
+            let x = 1;
+            qux!(a, b, a == b);
+        } else {
+            let x = 1;
+            qux!(a, b, a != b);
+        }
+    }
+}

tests/ui/branches_sharing_code/shared_at_top.stderr

@@ -125,5 +125,20 @@ note: the lint level is defined here
 LL | #![deny(clippy::branches_sharing_code, clippy::if_same_then_else)]
    |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 7 previous errors
+error: all if blocks contain the same code at the start
+  --> tests/ui/branches_sharing_code/shared_at_top.rs:148:9
+   |
+LL | /         if false {
+LL | |
+LL | |             let x = 1;
+   | |______________________^
+   |
+   = warning: some moved values might need to be renamed to avoid wrong references
+help: consider moving these statements before the if
+   |
+LL ~         let x = 1;
+LL +         if false {
+   |
+
+error: aborting due to 8 previous errors
 

tests/ui/branches_sharing_code/shared_at_top_and_bottom.rs

@@ -128,3 +128,42 @@ fn added_note_for_expression_use() -> u32 {
 }
 
 fn main() {}
+
+mod issue14873 {
+    fn foo() -> i32 {
+        todo!()
+    }
+
+    macro_rules! qux {
+        ($a:ident, $b:ident, $condition:expr) => {
+            let mut $a: i32 = foo();
+            let mut $b: i32 = foo();
+            if $condition {
+                "."
+            } else {
+                ""
+            };
+            $a = foo();
+            $b = foo();
+        };
+    }
+
+    fn share_on_top_and_bottom() {
+        if false {
+            qux!(a, b, a == b);
+        } else {
+            qux!(a, b, a != b);
+        };
+
+        if false {
+            //~^ branches_sharing_code
+            let x = 1;
+            qux!(a, b, a == b);
+            let y = 1;
+        } else {
+            let x = 1;
+            qux!(a, b, a != b);
+            let y = 1;
+        }
+    }
+}

tests/ui/branches_sharing_code/shared_at_top_and_bottom.stderr

@@ -159,5 +159,31 @@ LL ~     }
 LL +     x * 4
    |
 
-error: aborting due to 5 previous errors
+error: all if blocks contain the same code at both the start and the end
+  --> tests/ui/branches_sharing_code/shared_at_top_and_bottom.rs:158:9
+   |
+LL | /         if false {
+LL | |
+LL | |             let x = 1;
+   | |______________________^
+   |
+note: this code is shared at the end
+  --> tests/ui/branches_sharing_code/shared_at_top_and_bottom.rs:166:9
+   |
+LL | /             let y = 1;
+LL | |         }
+   | |_________^
+   = warning: some moved values might need to be renamed to avoid wrong references
+help: consider moving these statements before the if
+   |
+LL ~         let x = 1;
+LL +         if false {
+   |
+help: consider moving these statements after the if
+   |
+LL ~         }
+LL +         let y = 1;
+   |
+
+error: aborting due to 6 previous errors