2016-03-30 17:53:43 +00:00
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use rustc::lint::*;
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use rustc::hir;
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use syntax::codemap;
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use utils::{snippet, span_lint_and_then};
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/// **What it does:** This lint checks for variable declarations immediately followed by a
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/// conditional affectation.
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///
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/// **Why is this bad?** This is not idiomatic Rust.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust,ignore
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/// let foo;
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///
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/// if bar() {
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/// foo = 42;
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/// } else {
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/// foo = 0;
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/// }
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///
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/// let mut baz = None;
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///
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/// if bar() {
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/// baz = Some(42);
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/// }
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/// ```
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///
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/// should be written
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///
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/// ```rust,ignore
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/// let foo = if bar() {
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/// 42;
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/// } else {
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/// 0;
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/// };
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///
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/// let baz = if bar() {
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/// Some(42);
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/// } else {
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/// None
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/// };
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/// ```
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declare_lint! {
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pub USELESS_LET_IF_SEQ,
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Warn,
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"Checks for unidiomatic `let mut` declaration followed by initialization in `if`"
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}
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#[derive(Copy,Clone)]
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pub struct LetIfSeq;
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impl LintPass for LetIfSeq {
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fn get_lints(&self) -> LintArray {
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lint_array!(USELESS_LET_IF_SEQ)
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}
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}
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impl LateLintPass for LetIfSeq {
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fn check_block(&mut self, cx: &LateContext, block: &hir::Block) {
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let mut it = block.stmts.iter().peekable();
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2016-08-01 14:59:14 +00:00
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while let Some(stmt) = it.next() {
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2016-03-30 17:53:43 +00:00
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if_let_chain! {[
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let Some(expr) = it.peek(),
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let hir::StmtDecl(ref decl, _) = stmt.node,
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let hir::DeclLocal(ref decl) = decl.node,
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2016-05-31 20:07:03 +00:00
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let hir::PatKind::Binding(mode, ref name, None) = decl.pat.node,
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2016-03-30 17:53:43 +00:00
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let Some(def) = cx.tcx.def_map.borrow().get(&decl.pat.id),
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let hir::StmtExpr(ref if_, _) = expr.node,
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let hir::ExprIf(ref cond, ref then, ref else_) = if_.node,
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2016-06-10 17:47:10 +00:00
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!used_in_expr(cx, def.full_def().def_id(), cond),
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let Some(value) = check_assign(cx, def.full_def().def_id(), then),
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!used_in_expr(cx, def.full_def().def_id(), value),
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2016-03-30 17:53:43 +00:00
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], {
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let span = codemap::mk_sp(stmt.span.lo, if_.span.hi);
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let (default_multi_stmts, default) = if let Some(ref else_) = *else_ {
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if let hir::ExprBlock(ref else_) = else_.node {
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2016-06-10 17:47:10 +00:00
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if let Some(default) = check_assign(cx, def.full_def().def_id(), else_) {
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2016-03-30 17:53:43 +00:00
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(else_.stmts.len() > 1, default)
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} else if let Some(ref default) = decl.init {
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(true, &**default)
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} else {
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continue;
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}
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} else {
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continue;
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}
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} else if let Some(ref default) = decl.init {
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(false, &**default)
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} else {
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continue;
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};
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let mutability = match mode {
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hir::BindByRef(hir::MutMutable) | hir::BindByValue(hir::MutMutable) => "<mut> ",
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_ => "",
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};
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// FIXME: this should not suggest `mut` if we can detect that the variable is not
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// use mutably after the `if`
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let sug = format!(
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"let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
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mut=mutability,
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name=name.node,
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cond=snippet(cx, cond.span, "_"),
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then=if then.stmts.len() > 1 { " ..;" } else { "" },
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else=if default_multi_stmts { " ..;" } else { "" },
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value=snippet(cx, value.span, "<value>"),
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default=snippet(cx, default.span, "<default>"),
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);
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span_lint_and_then(cx,
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USELESS_LET_IF_SEQ,
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span,
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"`if _ { .. } else { .. }` is an expression",
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|db| {
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db.span_suggestion(span,
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"it is more idiomatic to write",
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sug);
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if !mutability.is_empty() {
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db.note("you might not need `mut` at all");
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}
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});
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}}
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}
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}
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}
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struct UsedVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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id: hir::def_id::DefId,
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used: bool,
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}
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impl<'a, 'tcx, 'v> hir::intravisit::Visitor<'v> for UsedVisitor<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &'v hir::Expr) {
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if_let_chain! {[
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let hir::ExprPath(None, _) = expr.node,
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let Some(def) = self.cx.tcx.def_map.borrow().get(&expr.id),
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2016-06-10 17:47:10 +00:00
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self.id == def.full_def().def_id(),
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2016-03-30 17:53:43 +00:00
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], {
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self.used = true;
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return;
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}}
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hir::intravisit::walk_expr(self, expr);
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}
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}
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fn check_assign<'e>(cx: &LateContext, decl: hir::def_id::DefId, block: &'e hir::Block) -> Option<&'e hir::Expr> {
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if_let_chain! {[
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2016-06-08 22:22:59 +00:00
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block.expr.is_none(),
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2016-03-30 17:53:43 +00:00
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let Some(expr) = block.stmts.iter().last(),
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let hir::StmtSemi(ref expr, _) = expr.node,
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let hir::ExprAssign(ref var, ref value) = expr.node,
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let hir::ExprPath(None, _) = var.node,
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let Some(def) = cx.tcx.def_map.borrow().get(&var.id),
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2016-06-10 17:47:10 +00:00
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decl == def.full_def().def_id(),
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2016-03-30 17:53:43 +00:00
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], {
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let mut v = UsedVisitor {
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cx: cx,
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id: decl,
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used: false,
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};
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for s in block.stmts.iter().take(block.stmts.len()-1) {
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hir::intravisit::walk_stmt(&mut v, s);
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2016-06-03 17:35:39 +00:00
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if v.used {
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return None;
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}
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2016-03-30 17:53:43 +00:00
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}
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2016-06-03 17:35:39 +00:00
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return Some(value);
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2016-03-30 17:53:43 +00:00
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}}
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None
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}
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2016-06-05 19:38:15 +00:00
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fn used_in_expr(cx: &LateContext, id: hir::def_id::DefId, expr: &hir::Expr) -> bool {
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let mut v = UsedVisitor {
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cx: cx,
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id: id,
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2016-06-05 23:42:39 +00:00
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used: false,
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2016-06-05 19:38:15 +00:00
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};
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hir::intravisit::walk_expr(&mut v, expr);
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v.used
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}
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