1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::source::snippet;
3 use clippy_utils::{path_to_local_id, visitors::is_local_used};
4 use if_chain::if_chain;
5 use rustc_errors::Applicability;
7 use rustc_hir::BindingAnnotation;
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 declare_clippy_lint! {
13 /// Checks for variable declarations immediately followed by a
14 /// conditional affectation.
16 /// ### Why is this bad?
17 /// This is not idiomatic Rust.
29 /// let mut baz = None;
39 /// let foo = if bar() {
45 /// let baz = if bar() {
51 pub USELESS_LET_IF_SEQ,
53 "unidiomatic `let mut` declaration followed by initialization in `if`"
56 declare_lint_pass!(LetIfSeq => [USELESS_LET_IF_SEQ]);
58 impl<'tcx> LateLintPass<'tcx> for LetIfSeq {
59 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
60 let mut it = block.stmts.iter().peekable();
61 while let Some(stmt) = it.next() {
63 if let Some(expr) = it.peek();
64 if let hir::StmtKind::Local(local) = stmt.kind;
65 if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.kind;
66 if let hir::StmtKind::Expr(if_) = expr.kind;
67 if let hir::ExprKind::If(hir::Expr { kind: hir::ExprKind::DropTemps(cond), ..}, then, else_) = if_.kind;
68 if !is_local_used(cx, *cond, canonical_id);
69 if let hir::ExprKind::Block(then, _) = then.kind;
70 if let Some(value) = check_assign(cx, canonical_id, &*then);
71 if !is_local_used(cx, value, canonical_id);
73 let span = stmt.span.to(if_.span);
75 let has_interior_mutability = !cx.typeck_results().node_type(canonical_id).is_freeze(
79 if has_interior_mutability { return; }
81 let (default_multi_stmts, default) = if let Some(else_) = else_ {
82 if let hir::ExprKind::Block(else_, _) = else_.kind {
83 if let Some(default) = check_assign(cx, canonical_id, else_) {
84 (else_.stmts.len() > 1, default)
85 } else if let Some(default) = local.init {
93 } else if let Some(default) = local.init {
99 let mutability = match mode {
100 BindingAnnotation::RefMut | BindingAnnotation::Mutable => "<mut> ",
104 // FIXME: this should not suggest `mut` if we can detect that the variable is not
105 // use mutably after the `if`
108 "let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
111 cond=snippet(cx, cond.span, "_"),
112 then=if then.stmts.len() > 1 { " ..;" } else { "" },
113 else=if default_multi_stmts { " ..;" } else { "" },
114 value=snippet(cx, value.span, "<value>"),
115 default=snippet(cx, default.span, "<default>"),
117 span_lint_and_then(cx,
120 "`if _ { .. } else { .. }` is an expression",
122 diag.span_suggestion(
124 "it is more idiomatic to write",
126 Applicability::HasPlaceholders,
128 if !mutability.is_empty() {
129 diag.note("you might not need `mut` at all");
138 fn check_assign<'tcx>(
139 cx: &LateContext<'tcx>,
141 block: &'tcx hir::Block<'_>,
142 ) -> Option<&'tcx hir::Expr<'tcx>> {
144 if block.expr.is_none();
145 if let Some(expr) = block.stmts.iter().last();
146 if let hir::StmtKind::Semi(expr) = expr.kind;
147 if let hir::ExprKind::Assign(var, value, _) = expr.kind;
148 if path_to_local_id(var, decl);
150 if block.stmts.iter().take(block.stmts.len()-1).any(|stmt| is_local_used(cx, stmt, decl)) {