205 lines
7.1 KiB
Rust
205 lines
7.1 KiB
Rust
use crate::utils::{higher, qpath_res, snippet, span_lint_and_then};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir as hir;
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use rustc_hir::def::Res;
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use rustc_hir::intravisit;
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use rustc_hir::BindingAnnotation;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::hir::map::Map;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// **What it does:** 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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pub USELESS_LET_IF_SEQ,
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nursery,
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"unidiomatic `let mut` declaration followed by initialization in `if`"
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}
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declare_lint_pass!(LetIfSeq => [USELESS_LET_IF_SEQ]);
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impl<'tcx> LateLintPass<'tcx> for LetIfSeq {
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fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
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let mut it = block.stmts.iter().peekable();
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while let Some(stmt) = it.next() {
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if_chain! {
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if let Some(expr) = it.peek();
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if let hir::StmtKind::Local(ref local) = stmt.kind;
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if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.kind;
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if let hir::StmtKind::Expr(ref if_) = expr.kind;
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if let Some((ref cond, ref then, ref else_)) = higher::if_block(&if_);
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if !used_in_expr(cx, canonical_id, cond);
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if let hir::ExprKind::Block(ref then, _) = then.kind;
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if let Some(value) = check_assign(cx, canonical_id, &*then);
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if !used_in_expr(cx, canonical_id, value);
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then {
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let span = stmt.span.to(if_.span);
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let has_interior_mutability = !cx.tables().node_type(canonical_id).is_freeze(
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cx.tcx.at(span),
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cx.param_env,
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);
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if has_interior_mutability { return; }
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let (default_multi_stmts, default) = if let Some(ref else_) = *else_ {
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if let hir::ExprKind::Block(ref else_, _) = else_.kind {
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if let Some(default) = check_assign(cx, canonical_id, else_) {
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(else_.stmts.len() > 1, default)
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} else if let Some(ref default) = local.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) = local.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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BindingAnnotation::RefMut | BindingAnnotation::Mutable => "<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=ident.name,
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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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|diag| {
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diag.span_suggestion(
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span,
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"it is more idiomatic to write",
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sug,
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Applicability::HasPlaceholders,
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);
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if !mutability.is_empty() {
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diag.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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}
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struct UsedVisitor<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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id: hir::HirId,
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used: bool,
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}
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impl<'a, 'tcx> intravisit::Visitor<'tcx> for UsedVisitor<'a, 'tcx> {
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type Map = Map<'tcx>;
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fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
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if_chain! {
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if let hir::ExprKind::Path(ref qpath) = expr.kind;
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if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id);
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if self.id == local_id;
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then {
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self.used = true;
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return;
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}
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}
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intravisit::walk_expr(self, expr);
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}
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fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
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intravisit::NestedVisitorMap::None
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}
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}
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fn check_assign<'tcx>(
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cx: &LateContext<'tcx>,
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decl: hir::HirId,
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block: &'tcx hir::Block<'_>,
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) -> Option<&'tcx hir::Expr<'tcx>> {
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if_chain! {
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if block.expr.is_none();
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if let Some(expr) = block.stmts.iter().last();
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if let hir::StmtKind::Semi(ref expr) = expr.kind;
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if let hir::ExprKind::Assign(ref var, ref value, _) = expr.kind;
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if let hir::ExprKind::Path(ref qpath) = var.kind;
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if let Res::Local(local_id) = qpath_res(cx, qpath, var.hir_id);
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if decl == local_id;
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then {
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let mut v = UsedVisitor {
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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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intravisit::walk_stmt(&mut v, s);
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if v.used {
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return None;
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}
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}
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return Some(value);
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}
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}
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None
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}
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fn used_in_expr<'tcx>(cx: &LateContext<'tcx>, id: hir::HirId, expr: &'tcx hir::Expr<'_>) -> bool {
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let mut v = UsedVisitor { cx, id, used: false };
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intravisit::walk_expr(&mut v, expr);
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v.used
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}
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