1 use crate::utils::{snippet, span_lint_and_then};
2 use if_chain::if_chain;
4 use rustc::hir::def::Def;
5 use rustc::hir::BindingAnnotation;
6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
7 use rustc::{declare_tool_lint, lint_array};
8 use rustc_errors::Applicability;
11 /// **What it does:** Checks for variable declarations immediately followed by a
12 /// conditional affectation.
14 /// **Why is this bad?** This is not idiomatic Rust.
16 /// **Known problems:** None.
28 /// let mut baz = None;
38 /// let foo = if bar() {
44 /// let baz = if bar() {
50 declare_clippy_lint! {
51 pub USELESS_LET_IF_SEQ,
53 "unidiomatic `let mut` declaration followed by initialization in `if`"
56 #[derive(Copy, Clone)]
59 impl LintPass for LetIfSeq {
60 fn get_lints(&self) -> LintArray {
61 lint_array!(USELESS_LET_IF_SEQ)
65 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetIfSeq {
66 fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block) {
67 let mut it = block.stmts.iter().peekable();
68 while let Some(stmt) = it.next() {
70 if let Some(expr) = it.peek();
71 if let hir::StmtKind::Local(ref local) = stmt.node;
72 if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.node;
73 if let hir::StmtKind::Expr(ref if_) = expr.node;
74 if let hir::ExprKind::If(ref cond, ref then, ref else_) = if_.node;
75 if !used_in_expr(cx, canonical_id, cond);
76 if let hir::ExprKind::Block(ref then, _) = then.node;
77 if let Some(value) = check_assign(cx, canonical_id, &*then);
78 if !used_in_expr(cx, canonical_id, value);
80 let span = stmt.span.to(if_.span);
82 let (default_multi_stmts, default) = if let Some(ref else_) = *else_ {
83 if let hir::ExprKind::Block(ref else_, _) = else_.node {
84 if let Some(default) = check_assign(cx, canonical_id, else_) {
85 (else_.stmts.len() > 1, default)
86 } else if let Some(ref default) = local.init {
94 } else if let Some(ref default) = local.init {
100 let mutability = match mode {
101 BindingAnnotation::RefMut | BindingAnnotation::Mutable => "<mut> ",
105 // FIXME: this should not suggest `mut` if we can detect that the variable is not
106 // use mutably after the `if`
109 "let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
112 cond=snippet(cx, cond.span, "_"),
113 then=if then.stmts.len() > 1 { " ..;" } else { "" },
114 else=if default_multi_stmts { " ..;" } else { "" },
115 value=snippet(cx, value.span, "<value>"),
116 default=snippet(cx, default.span, "<default>"),
118 span_lint_and_then(cx,
121 "`if _ { .. } else { .. }` is an expression",
123 db.span_suggestion_with_applicability(
125 "it is more idiomatic to write",
127 Applicability::HasPlaceholders,
129 if !mutability.is_empty() {
130 db.note("you might not need `mut` at all");
139 struct UsedVisitor<'a, 'tcx: 'a> {
140 cx: &'a LateContext<'a, 'tcx>,
145 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UsedVisitor<'a, 'tcx> {
146 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
148 if let hir::ExprKind::Path(ref qpath) = expr.node;
149 if let Def::Local(local_id) = self.cx.tables.qpath_def(qpath, expr.hir_id);
150 if self.id == local_id;
156 hir::intravisit::walk_expr(self, expr);
158 fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
159 hir::intravisit::NestedVisitorMap::None
163 fn check_assign<'a, 'tcx>(
164 cx: &LateContext<'a, 'tcx>,
166 block: &'tcx hir::Block,
167 ) -> Option<&'tcx hir::Expr> {
169 if block.expr.is_none();
170 if let Some(expr) = block.stmts.iter().last();
171 if let hir::StmtKind::Semi(ref expr) = expr.node;
172 if let hir::ExprKind::Assign(ref var, ref value) = expr.node;
173 if let hir::ExprKind::Path(ref qpath) = var.node;
174 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, var.hir_id);
177 let mut v = UsedVisitor {
183 for s in block.stmts.iter().take(block.stmts.len()-1) {
184 hir::intravisit::walk_stmt(&mut v, s);
198 fn used_in_expr<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, id: ast::NodeId, expr: &'tcx hir::Expr) -> bool {
199 let mut v = UsedVisitor { cx, id, used: false };
200 hir::intravisit::walk_expr(&mut v, expr);