330 lines
12 KiB
Rust
330 lines
12 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::higher;
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use clippy_utils::ty::is_type_diagnostic_item;
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use clippy_utils::{path_to_local, usage::is_potentially_mutated};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, Visitor};
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use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, PathSegment, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::hir::nested_filter;
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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
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/// Checks for calls of `unwrap[_err]()` that cannot fail.
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///
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/// ### Why is this bad?
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/// Using `if let` or `match` is more idiomatic.
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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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#[clippy::version = "pre 1.29.0"]
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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
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/// Checks for calls of `unwrap[_err]()` that will always fail.
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///
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/// ### Why is this bad?
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/// If panicking is desired, an explicit `panic!()` should be used.
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///
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/// ### Known problems
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/// 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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#[clippy::version = "pre 1.29.0"]
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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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/// What kind of unwrappable this is.
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#[derive(Copy, Clone, Debug)]
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enum UnwrappableKind {
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Option,
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Result,
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}
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impl UnwrappableKind {
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fn success_variant_pattern(self) -> &'static str {
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match self {
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UnwrappableKind::Option => "Some(..)",
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UnwrappableKind::Result => "Ok(..)",
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}
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}
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fn error_variant_pattern(self) -> &'static str {
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match self {
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UnwrappableKind::Option => "None",
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UnwrappableKind::Result => "Err(..)",
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}
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}
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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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local_id: HirId,
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/// The if itself
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if_expr: &'tcx Expr<'tcx>,
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/// The check, like `x.is_ok()`
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check: &'tcx Expr<'tcx>,
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/// The check's name, like `is_ok`
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check_name: &'tcx PathSegment<'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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/// What kind of unwrappable this is.
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kind: UnwrappableKind,
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/// If the check is the entire condition (`if x.is_ok()`) or only a part of it (`foo() &&
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/// x.is_ok()`)
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is_entire_condition: 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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if_expr: &'tcx Expr<'_>,
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expr: &'tcx Expr<'_>,
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branch: &'tcx Expr<'_>,
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invert: bool,
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is_entire_condition: 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) && ["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) && ["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, if_expr, left, branch, invert, false);
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unwrap_info.append(&mut collect_unwrap_info(cx, if_expr, right, branch, invert, false));
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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, if_expr, expr, branch, !invert, false);
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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 Some(local_id) = path_to_local(&args[0]);
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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 {
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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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let kind = if is_type_diagnostic_item(cx, ty, sym::Option) {
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UnwrappableKind::Option
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} else {
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UnwrappableKind::Result
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};
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return vec![
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UnwrapInfo {
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local_id,
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if_expr,
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check: expr,
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check_name: method_name,
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branch,
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safe_to_unwrap,
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kind,
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is_entire_condition,
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}
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]
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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(
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&mut self,
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if_expr: &'tcx Expr<'_>,
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cond: &'tcx Expr<'_>,
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branch: &'tcx Expr<'_>,
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else_branch: bool,
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) {
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let prev_len = self.unwrappables.len();
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for unwrap_info in collect_unwrap_info(self.cx, if_expr, cond, branch, else_branch, true) {
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if is_potentially_mutated(unwrap_info.local_id, cond, self.cx)
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|| is_potentially_mutated(unwrap_info.local_id, 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 NestedFilter = nested_filter::OnlyBodies;
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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 Some(higher::If { cond, then, r#else }) = higher::If::hir(expr) {
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walk_expr(self, cond);
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self.visit_branch(expr, cond, then, false);
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if let Some(else_inner) = r#else {
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self.visit_branch(expr, cond, else_inner, 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, [self_arg, ..], _) = expr.kind;
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if let Some(id) = path_to_local(self_arg);
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if [sym::unwrap, sym::expect, sym!(unwrap_err)].contains(&method_name.ident.name);
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let call_to_unwrap = [sym::unwrap, sym::expect].contains(&method_name.ident.name);
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if let Some(unwrappable) = self.unwrappables.iter()
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.find(|u| u.local_id == id);
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// Span contexts should not differ with the conditional branch
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let span_ctxt = expr.span.ctxt();
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if unwrappable.branch.span.ctxt() == span_ctxt;
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if unwrappable.check.span.ctxt() == span_ctxt;
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then {
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if call_to_unwrap == unwrappable.safe_to_unwrap {
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let is_entire_condition = unwrappable.is_entire_condition;
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let unwrappable_variable_name = self.cx.tcx.hir().name(unwrappable.local_id);
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let suggested_pattern = if call_to_unwrap {
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unwrappable.kind.success_variant_pattern()
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} else {
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unwrappable.kind.error_variant_pattern()
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};
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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!(
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"called `{}` on `{}` after checking its variant with `{}`",
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method_name.ident.name,
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unwrappable_variable_name,
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unwrappable.check_name.ident.as_str(),
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),
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|diag| {
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if is_entire_condition {
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diag.span_suggestion(
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unwrappable.check.span.with_lo(unwrappable.if_expr.span.lo()),
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"try",
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format!(
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"if let {} = {}",
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suggested_pattern,
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unwrappable_variable_name,
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),
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// We don't track how the unwrapped value is used inside the
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// block or suggest deleting the unwrap, so we can't offer a
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// fixable solution.
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Applicability::Unspecified,
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);
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} else {
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diag.span_label(unwrappable.check.span, "the check is happening here");
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diag.help("try using `if let` or `match`");
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}
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},
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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) -> Self::Map {
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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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