autofix for redundant_else lint (#13936)

changelog: [`redundant_else`]: autofix for some cases

`redundant_else` can be fixed automatically.

clippy_lints/src/redundant_else.rs

@@ -1,9 +1,13 @@
-use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::{indent_of, reindent_multiline, snippet};
 use rustc_ast::ast::{Block, Expr, ExprKind, Stmt, StmtKind};
 use rustc_ast::visit::{Visitor, walk_expr};
+use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+use std::borrow::Cow;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -76,13 +80,27 @@ impl EarlyLintPass for RedundantElse {
                 _ => break,
             }
         }
-        span_lint_and_help(
+
+        let mut app = Applicability::MachineApplicable;
+        if let ExprKind::Block(block, _) = &els.kind {
+            for stmt in &block.stmts {
+                // If the `else` block contains a local binding or a macro invocation, Clippy shouldn't auto-fix it
+                if matches!(&stmt.kind, StmtKind::Let(_) | StmtKind::MacCall(_)) {
+                    app = Applicability::Unspecified;
+                    break;
+                }
+            }
+        }
+
+        // FIXME: The indentation of the suggestion would be the same as the one of the macro invocation in this implementation, see https://github.com/rust-lang/rust-clippy/pull/13936#issuecomment-2569548202
+        span_lint_and_sugg(
             cx,
             REDUNDANT_ELSE,
-            els.span,
+            els.span.with_lo(then.span.hi()),
             "redundant else block",
-            None,
             "remove the `else` block and move the contents out",
+            make_sugg(cx, els.span, "..", Some(expr.span)).to_string(),
+            app,
         );
     }
 }
@@ -137,3 +155,23 @@ impl BreakVisitor {
         self.check(stmt, Self::visit_stmt)
     }
 }
+
+// Extract the inner contents of an `else` block str
+// e.g. `{ foo(); bar(); }` -> `foo(); bar();`
+fn extract_else_block(mut block: &str) -> String {
+    block = block.strip_prefix("{").unwrap_or(block);
+    block = block.strip_suffix("}").unwrap_or(block);
+    block.trim_end().to_string()
+}
+
+fn make_sugg<'a>(
+    cx: &EarlyContext<'_>,
+    els_span: Span,
+    default: &'a str,
+    indent_relative_to: Option<Span>,
+) -> Cow<'a, str> {
+    let extracted = extract_else_block(&snippet(cx, els_span, default));
+    let indent = indent_relative_to.and_then(|s| indent_of(cx, s));
+
+    reindent_multiline(extracted.into(), false, indent)
+}

tests/ui/redundant_else.fixed

@@ -0,0 +1,154 @@
+#![warn(clippy::redundant_else)]
+#![allow(clippy::needless_return, clippy::if_same_then_else, clippy::needless_late_init)]
+
+fn main() {
+    loop {
+        // break
+        if foo() {
+            println!("Love your neighbor;");
+            break;
+        }
+        //~^ ERROR: redundant else block
+        println!("yet don't pull down your hedge.");
+        // continue
+        if foo() {
+            println!("He that lies down with Dogs,");
+            continue;
+        }
+        //~^ ERROR: redundant else block
+        println!("shall rise up with fleas.");
+        // match block
+        if foo() {
+            match foo() {
+                1 => break,
+                _ => return,
+            }
+        }
+        //~^ ERROR: redundant else block
+        println!("You may delay, but time will not.");
+    }
+    // else if
+    if foo() {
+        return;
+    } else if foo() {
+        return;
+    }
+    //~^ ERROR: redundant else block
+    println!("A fat kitchen makes a lean will.");
+    // let binding outside of block
+    let _ = {
+        if foo() {
+            return;
+        }
+        //~^ ERROR: redundant else block
+        1
+    };
+    // else if with let binding outside of block
+    let _ = {
+        if foo() {
+            return;
+        } else if foo() {
+            return;
+        }
+        //~^ ERROR: redundant else block
+        2
+    };
+    // inside if let
+    let _ = if let Some(1) = foo() {
+        let _ = 1;
+        if foo() {
+            return;
+        }
+        //~^ ERROR: redundant else block
+        1
+    } else {
+        1
+    };
+
+    //
+    // non-lint cases
+    //
+
+    // sanity check
+    if foo() {
+        let _ = 1;
+    } else {
+        println!("Who is wise? He that learns from every one.");
+    }
+    // else if without else
+    if foo() {
+        return;
+    } else if foo() {
+        foo()
+    };
+    // nested if return
+    if foo() {
+        if foo() {
+            return;
+        }
+    } else {
+        foo()
+    };
+    // match with non-breaking branch
+    if foo() {
+        match foo() {
+            1 => foo(),
+            _ => return,
+        }
+    } else {
+        println!("Three may keep a secret, if two of them are dead.");
+    }
+    // let binding
+    let _ = if foo() {
+        return;
+    } else {
+        1
+    };
+    // assign
+    let mut a;
+    a = if foo() {
+        return;
+    } else {
+        1
+    };
+    // assign-op
+    a += if foo() {
+        return;
+    } else {
+        1
+    };
+    // if return else if else
+    if foo() {
+        return;
+    } else if foo() {
+        1
+    } else {
+        2
+    };
+    // if else if return else
+    if foo() {
+        1
+    } else if foo() {
+        return;
+    } else {
+        2
+    };
+    // else if with let binding
+    let _ = if foo() {
+        return;
+    } else if foo() {
+        return;
+    } else {
+        2
+    };
+    // inside function call
+    Box::new(if foo() {
+        return;
+    } else {
+        1
+    });
+}
+
+fn foo<T>() -> T {
+    unimplemented!("I'm not Santa Claus")
+}

tests/ui/redundant_else.stderr

@@ -1,88 +1,123 @@
 error: redundant else block
-  --> tests/ui/redundant_else.rs:10:16
+  --> tests/ui/redundant_else.rs:10:10
    |
 LL |           } else {
-   |  ________________^
+   |  __________^
 LL | |
 LL | |             println!("yet don't pull down your hedge.");
 LL | |         }
    | |_________^
    |
-   = help: remove the `else` block and move the contents out
    = note: `-D clippy::redundant-else` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::redundant_else)]`
+help: remove the `else` block and move the contents out
+   |
+LL ~         }
+LL +
+LL +         println!("yet don't pull down your hedge.");
+   |
 
 error: redundant else block
-  --> tests/ui/redundant_else.rs:18:16
+  --> tests/ui/redundant_else.rs:18:10
    |
 LL |           } else {
-   |  ________________^
+   |  __________^
 LL | |
 LL | |             println!("shall rise up with fleas.");
 LL | |         }
    | |_________^
    |
-   = help: remove the `else` block and move the contents out
+help: remove the `else` block and move the contents out
+   |
+LL ~         }
+LL +
+LL +         println!("shall rise up with fleas.");
+   |
 
 error: redundant else block
-  --> tests/ui/redundant_else.rs:28:16
+  --> tests/ui/redundant_else.rs:28:10
    |
 LL |           } else {
-   |  ________________^
+   |  __________^
 LL | |
 LL | |             println!("You may delay, but time will not.");
 LL | |         }
    | |_________^
    |
-   = help: remove the `else` block and move the contents out
+help: remove the `else` block and move the contents out
+   |
+LL ~         }
+LL +
+LL +         println!("You may delay, but time will not.");
+   |
 
 error: redundant else block
-  --> tests/ui/redundant_else.rs:38:12
+  --> tests/ui/redundant_else.rs:38:6
    |
 LL |       } else {
-   |  ____________^
+   |  ______^
 LL | |
 LL | |         println!("A fat kitchen makes a lean will.");
 LL | |     }
    | |_____^
    |
-   = help: remove the `else` block and move the contents out
+help: remove the `else` block and move the contents out
+   |
+LL ~     }
+LL +
+LL +     println!("A fat kitchen makes a lean will.");
+   |
 
 error: redundant else block
-  --> tests/ui/redundant_else.rs:46:16
+  --> tests/ui/redundant_else.rs:46:10
    |
 LL |           } else {
-   |  ________________^
+   |  __________^
 LL | |
 LL | |             1
 LL | |         }
    | |_________^
    |
-   = help: remove the `else` block and move the contents out
+help: remove the `else` block and move the contents out
+   |
+LL ~         }
+LL +
+LL +         1
+   |
 
 error: redundant else block
-  --> tests/ui/redundant_else.rs:57:16
+  --> tests/ui/redundant_else.rs:57:10
    |
 LL |           } else {
-   |  ________________^
+   |  __________^
 LL | |
 LL | |             2
 LL | |         }
    | |_________^
    |
-   = help: remove the `else` block and move the contents out
+help: remove the `else` block and move the contents out
+   |
+LL ~         }
+LL +
+LL +         2
+   |
 
 error: redundant else block
-  --> tests/ui/redundant_else.rs:67:16
+  --> tests/ui/redundant_else.rs:67:10
    |
 LL |           } else {
-   |  ________________^
+   |  __________^
 LL | |
 LL | |             1
 LL | |         }
    | |_________^
    |
-   = help: remove the `else` block and move the contents out
+help: remove the `else` block and move the contents out
+   |
+LL ~         }
+LL +
+LL +         1
+   |
 
 error: aborting due to 7 previous errors