4 use utils::{snippet, span_lint_and_then};
6 /// **What it does:** Checks for variable declarations immediately followed by a
7 /// conditional affectation.
9 /// **Why is this bad?** This is not idiomatic Rust.
11 /// **Known problems:** None.
23 /// let mut baz = None;
33 /// let foo = if bar() {
39 /// let baz = if bar() {
46 pub USELESS_LET_IF_SEQ,
48 "unidiomatic `let mut` declaration followed by initialization in `if`"
54 impl LintPass for LetIfSeq {
55 fn get_lints(&self) -> LintArray {
56 lint_array!(USELESS_LET_IF_SEQ)
60 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetIfSeq {
61 fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block) {
62 let mut it = block.stmts.iter().peekable();
63 while let Some(stmt) = it.next() {
65 let Some(expr) = it.peek(),
66 let hir::StmtDecl(ref decl, _) = stmt.node,
67 let hir::DeclLocal(ref decl) = decl.node,
68 let hir::PatKind::Binding(mode, def_id, ref name, None) = decl.pat.node,
69 let hir::StmtExpr(ref if_, _) = expr.node,
70 let hir::ExprIf(ref cond, ref then, ref else_) = if_.node,
71 !used_in_expr(cx, def_id, cond),
72 let Some(value) = check_assign(cx, def_id, then),
73 !used_in_expr(cx, def_id, value),
75 let span = codemap::mk_sp(stmt.span.lo, if_.span.hi);
77 let (default_multi_stmts, default) = if let Some(ref else_) = *else_ {
78 if let hir::ExprBlock(ref else_) = else_.node {
79 if let Some(default) = check_assign(cx, def_id, else_) {
80 (else_.stmts.len() > 1, default)
81 } else if let Some(ref default) = decl.init {
89 } else if let Some(ref default) = decl.init {
95 let mutability = match mode {
96 hir::BindByRef(hir::MutMutable) | hir::BindByValue(hir::MutMutable) => "<mut> ",
100 // FIXME: this should not suggest `mut` if we can detect that the variable is not
101 // use mutably after the `if`
104 "let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
107 cond=snippet(cx, cond.span, "_"),
108 then=if then.stmts.len() > 1 { " ..;" } else { "" },
109 else=if default_multi_stmts { " ..;" } else { "" },
110 value=snippet(cx, value.span, "<value>"),
111 default=snippet(cx, default.span, "<default>"),
113 span_lint_and_then(cx,
116 "`if _ { .. } else { .. }` is an expression",
118 db.span_suggestion(span,
119 "it is more idiomatic to write",
121 if !mutability.is_empty() {
122 db.note("you might not need `mut` at all");
130 struct UsedVisitor<'a, 'tcx: 'a> {
131 cx: &'a LateContext<'a, 'tcx>,
132 id: hir::def_id::DefId,
136 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UsedVisitor<'a, 'tcx> {
137 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
139 let hir::ExprPath(ref qpath) = expr.node,
140 self.id == self.cx.tcx.tables().qpath_def(qpath, expr.id).def_id(),
145 hir::intravisit::walk_expr(self, expr);
147 fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
148 hir::intravisit::NestedVisitorMap::All(&self.cx.tcx.map)
152 fn check_assign<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, decl: hir::def_id::DefId, block: &'tcx hir::Block)
153 -> Option<&'tcx hir::Expr> {
155 block.expr.is_none(),
156 let Some(expr) = block.stmts.iter().last(),
157 let hir::StmtSemi(ref expr, _) = expr.node,
158 let hir::ExprAssign(ref var, ref value) = expr.node,
159 let hir::ExprPath(ref qpath) = var.node,
160 decl == cx.tcx.tables().qpath_def(qpath, var.id).def_id(),
162 let mut v = UsedVisitor {
168 for s in block.stmts.iter().take(block.stmts.len()-1) {
169 hir::intravisit::walk_stmt(&mut v, s);
182 fn used_in_expr<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, id: hir::def_id::DefId, expr: &'tcx hir::Expr) -> bool {
183 let mut v = UsedVisitor {
188 hir::intravisit::walk_expr(&mut v, expr);