234 lines
8.8 KiB
Rust
234 lines
8.8 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::ty::is_type_diagnostic_item;
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use clippy_utils::{differing_macro_contexts, usage::is_potentially_mutated};
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use if_chain::if_chain;
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use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
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use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, Path, QPath, UnOp};
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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_middle::lint::in_external_macro;
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use rustc_middle::ty::Ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::sym;
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declare_clippy_lint! {
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/// **What it does:** Checks for calls of `unwrap[_err]()` that cannot fail.
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///
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/// **Why is this bad?** Using `if let` or `match` is more idiomatic.
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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
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/// # let option = Some(0);
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/// # fn do_something_with(_x: usize) {}
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/// if option.is_some() {
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/// do_something_with(option.unwrap())
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/// }
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/// ```
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///
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/// Could be written:
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///
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/// ```rust
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/// # let option = Some(0);
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/// # fn do_something_with(_x: usize) {}
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/// if let Some(value) = option {
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/// do_something_with(value)
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/// }
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/// ```
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pub UNNECESSARY_UNWRAP,
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complexity,
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"checks for calls of `unwrap[_err]()` that cannot fail"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for calls of `unwrap[_err]()` that will always fail.
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///
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/// **Why is this bad?** If panicking is desired, an explicit `panic!()` should be used.
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///
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/// **Known problems:** This lint only checks `if` conditions not assignments.
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/// So something like `let x: Option<()> = None; x.unwrap();` will not be recognized.
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///
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/// **Example:**
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/// ```rust
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/// # let option = Some(0);
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/// # fn do_something_with(_x: usize) {}
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/// if option.is_none() {
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/// do_something_with(option.unwrap())
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/// }
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/// ```
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///
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/// This code will always panic. The if condition should probably be inverted.
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pub PANICKING_UNWRAP,
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correctness,
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"checks for calls of `unwrap[_err]()` that will always fail"
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}
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/// Visitor that keeps track of which variables are unwrappable.
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struct UnwrappableVariablesVisitor<'a, 'tcx> {
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unwrappables: Vec<UnwrapInfo<'tcx>>,
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cx: &'a LateContext<'tcx>,
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}
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/// Contains information about whether a variable can be unwrapped.
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#[derive(Copy, Clone, Debug)]
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struct UnwrapInfo<'tcx> {
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/// The variable that is checked
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ident: &'tcx Path<'tcx>,
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/// The check, like `x.is_ok()`
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check: &'tcx Expr<'tcx>,
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/// The branch where the check takes place, like `if x.is_ok() { .. }`
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branch: &'tcx Expr<'tcx>,
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/// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
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safe_to_unwrap: bool,
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}
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/// Collects the information about unwrappable variables from an if condition
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/// The `invert` argument tells us whether the condition is negated.
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fn collect_unwrap_info<'tcx>(
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cx: &LateContext<'tcx>,
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expr: &'tcx Expr<'_>,
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branch: &'tcx Expr<'_>,
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invert: bool,
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) -> Vec<UnwrapInfo<'tcx>> {
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fn is_relevant_option_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
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is_type_diagnostic_item(cx, ty, sym::option_type) && ["is_some", "is_none"].contains(&method_name)
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}
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fn is_relevant_result_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
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is_type_diagnostic_item(cx, ty, sym::result_type) && ["is_ok", "is_err"].contains(&method_name)
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}
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if let ExprKind::Binary(op, left, right) = &expr.kind {
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match (invert, op.node) {
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(false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
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let mut unwrap_info = collect_unwrap_info(cx, left, branch, invert);
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unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
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return unwrap_info;
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},
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_ => (),
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}
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} else if let ExprKind::Unary(UnOp::Not, expr) = &expr.kind {
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return collect_unwrap_info(cx, expr, branch, !invert);
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} else {
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if_chain! {
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if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
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if let ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
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let ty = cx.typeck_results().expr_ty(&args[0]);
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let name = method_name.ident.as_str();
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if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
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then {
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assert!(args.len() == 1);
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let unwrappable = match name.as_ref() {
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"is_some" | "is_ok" => true,
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"is_err" | "is_none" => false,
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_ => unreachable!(),
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};
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let safe_to_unwrap = unwrappable != invert;
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return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
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}
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}
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}
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Vec::new()
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}
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impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
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fn visit_branch(&mut self, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
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let prev_len = self.unwrappables.len();
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for unwrap_info in collect_unwrap_info(self.cx, cond, branch, else_branch) {
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if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
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|| is_potentially_mutated(unwrap_info.ident, branch, self.cx)
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{
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// if the variable is mutated, we don't know whether it can be unwrapped:
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continue;
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}
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self.unwrappables.push(unwrap_info);
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}
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walk_expr(self, branch);
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self.unwrappables.truncate(prev_len);
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
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type Map = Map<'tcx>;
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fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
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// Shouldn't lint when `expr` is in macro.
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if in_external_macro(self.cx.tcx.sess, expr.span) {
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return;
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}
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if let ExprKind::If(cond, then, els) = &expr.kind {
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walk_expr(self, cond);
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self.visit_branch(cond, then, false);
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if let Some(els) = els {
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self.visit_branch(cond, els, true);
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}
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} else {
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// find `unwrap[_err]()` calls:
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if_chain! {
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if let ExprKind::MethodCall(method_name, _, args, _) = expr.kind;
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if let ExprKind::Path(QPath::Resolved(None, path)) = args[0].kind;
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if [sym::unwrap, sym!(unwrap_err)].contains(&method_name.ident.name);
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let call_to_unwrap = method_name.ident.name == sym::unwrap;
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if let Some(unwrappable) = self.unwrappables.iter()
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.find(|u| u.ident.res == path.res);
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// Span contexts should not differ with the conditional branch
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if !differing_macro_contexts(unwrappable.branch.span, expr.span);
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if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
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then {
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if call_to_unwrap == unwrappable.safe_to_unwrap {
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span_lint_and_then(
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self.cx,
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UNNECESSARY_UNWRAP,
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expr.span,
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&format!("you checked before that `{}()` cannot fail, \
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instead of checking and unwrapping, it's better to use `if let` or `match`",
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method_name.ident.name),
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|diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
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);
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} else {
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span_lint_and_then(
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self.cx,
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PANICKING_UNWRAP,
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expr.span,
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&format!("this call to `{}()` will always panic",
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method_name.ident.name),
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|diag| { diag.span_label(unwrappable.check.span, "because of this check"); },
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);
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}
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}
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}
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walk_expr(self, expr);
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}
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}
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
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}
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}
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declare_lint_pass!(Unwrap => [PANICKING_UNWRAP, UNNECESSARY_UNWRAP]);
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impl<'tcx> LateLintPass<'tcx> for Unwrap {
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fn check_fn(
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&mut self,
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cx: &LateContext<'tcx>,
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kind: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
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span: Span,
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fn_id: HirId,
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) {
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if span.from_expansion() {
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return;
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}
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let mut v = UnwrappableVariablesVisitor {
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cx,
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unwrappables: Vec::new(),
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};
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walk_fn(&mut v, kind, decl, body.id(), span, fn_id);
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}
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}
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