rust-clippy/clippy_lints/src/unwrap.rs

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use clippy_utils::diagnostics::span_lint_hir_and_then;
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use clippy_utils::higher;
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;
use rustc_errors::Applicability;
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use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, Visitor};
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;
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::Ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for calls of `unwrap[_err]()` that cannot fail.
///
/// ### Why is this bad?
/// Using `if let` or `match` is more idiomatic.
///
/// ### Example
/// ```rust
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/// # let option = Some(0);
/// # fn do_something_with(_x: usize) {}
/// if option.is_some() {
/// do_something_with(option.unwrap())
/// }
/// ```
///
/// Could be written:
///
/// ```rust
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/// # let option = Some(0);
/// # fn do_something_with(_x: usize) {}
/// if let Some(value) = option {
/// do_something_with(value)
/// }
/// ```
#[clippy::version = "pre 1.29.0"]
pub UNNECESSARY_UNWRAP,
complexity,
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"checks for calls of `unwrap[_err]()` that cannot fail"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for calls of `unwrap[_err]()` that will always fail.
///
/// ### Why is this bad?
/// If panicking is desired, an explicit `panic!()` should be used.
///
/// ### Known problems
/// This lint only checks `if` conditions not assignments.
/// So something like `let x: Option<()> = None; x.unwrap();` will not be recognized.
///
/// ### Example
/// ```rust
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/// # let option = Some(0);
/// # fn do_something_with(_x: usize) {}
/// if option.is_none() {
/// do_something_with(option.unwrap())
/// }
/// ```
///
/// This code will always panic. The if condition should probably be inverted.
#[clippy::version = "pre 1.29.0"]
pub PANICKING_UNWRAP,
correctness,
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"checks for calls of `unwrap[_err]()` that will always fail"
}
/// Visitor that keeps track of which variables are unwrappable.
struct UnwrappableVariablesVisitor<'a, 'tcx> {
unwrappables: Vec<UnwrapInfo<'tcx>>,
cx: &'a LateContext<'tcx>,
}
/// What kind of unwrappable this is.
#[derive(Copy, Clone, Debug)]
enum UnwrappableKind {
Option,
Result,
}
impl UnwrappableKind {
fn success_variant_pattern(self) -> &'static str {
match self {
UnwrappableKind::Option => "Some(..)",
UnwrappableKind::Result => "Ok(..)",
}
}
fn error_variant_pattern(self) -> &'static str {
match self {
UnwrappableKind::Option => "None",
UnwrappableKind::Result => "Err(..)",
}
}
}
/// Contains information about whether a variable can be unwrapped.
#[derive(Copy, Clone, Debug)]
struct UnwrapInfo<'tcx> {
/// The variable that is checked
local_id: HirId,
/// The if itself
if_expr: &'tcx Expr<'tcx>,
/// The check, like `x.is_ok()`
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check: &'tcx Expr<'tcx>,
/// The check's name, like `is_ok`
check_name: &'tcx PathSegment<'tcx>,
/// The branch where the check takes place, like `if x.is_ok() { .. }`
branch: &'tcx Expr<'tcx>,
/// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
safe_to_unwrap: bool,
/// What kind of unwrappable this is.
kind: UnwrappableKind,
/// If the check is the entire condition (`if x.is_ok()`) or only a part of it (`foo() &&
/// x.is_ok()`)
is_entire_condition: bool,
}
/// Collects the information about unwrappable variables from an if condition
/// The `invert` argument tells us whether the condition is negated.
fn collect_unwrap_info<'tcx>(
cx: &LateContext<'tcx>,
if_expr: &'tcx Expr<'_>,
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expr: &'tcx Expr<'_>,
branch: &'tcx Expr<'_>,
invert: bool,
is_entire_condition: bool,
) -> Vec<UnwrapInfo<'tcx>> {
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)
}
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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if let ExprKind::Binary(op, left, right) = &expr.kind {
match (invert, op.node) {
(false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
let mut unwrap_info = collect_unwrap_info(cx, if_expr, left, branch, invert, false);
unwrap_info.append(&mut collect_unwrap_info(cx, if_expr, right, branch, invert, false));
return unwrap_info;
},
_ => (),
}
} else if let ExprKind::Unary(UnOp::Not, expr) = &expr.kind {
return collect_unwrap_info(cx, if_expr, expr, branch, !invert, false);
} else {
if_chain! {
if let ExprKind::MethodCall(method_name, args, _) = &expr.kind;
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();
if is_relevant_option_call(cx, ty, name) || is_relevant_result_call(cx, ty, name);
then {
assert!(args.len() == 1);
let unwrappable = match name {
"is_some" | "is_ok" => true,
"is_err" | "is_none" => false,
_ => unreachable!(),
};
let safe_to_unwrap = unwrappable != invert;
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let kind = if is_type_diagnostic_item(cx, ty, sym::Option) {
UnwrappableKind::Option
} else {
UnwrappableKind::Result
};
return vec![
UnwrapInfo {
local_id,
if_expr,
check: expr,
check_name: method_name,
branch,
safe_to_unwrap,
kind,
is_entire_condition,
}
]
}
}
}
Vec::new()
}
impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
fn visit_branch(
&mut self,
if_expr: &'tcx Expr<'_>,
cond: &'tcx Expr<'_>,
branch: &'tcx Expr<'_>,
else_branch: bool,
) {
let prev_len = self.unwrappables.len();
for unwrap_info in collect_unwrap_info(self.cx, if_expr, cond, branch, else_branch, true) {
if is_potentially_mutated(unwrap_info.local_id, cond, self.cx)
|| is_potentially_mutated(unwrap_info.local_id, branch, self.cx)
{
// if the variable is mutated, we don't know whether it can be unwrapped:
continue;
}
self.unwrappables.push(unwrap_info);
}
walk_expr(self, branch);
self.unwrappables.truncate(prev_len);
}
}
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<'_>) {
// Shouldn't lint when `expr` is in macro.
if in_external_macro(self.cx.tcx.sess, expr.span) {
return;
}
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if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr) {
walk_expr(self, cond);
self.visit_branch(expr, cond, then, false);
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if let Some(else_inner) = r#else {
self.visit_branch(expr, cond, else_inner, true);
}
} else {
// find `unwrap[_err]()` calls:
if_chain! {
if let ExprKind::MethodCall(method_name, [self_arg, ..], _) = expr.kind;
if let Some(id) = path_to_local(self_arg);
if [sym::unwrap, sym::expect, sym!(unwrap_err)].contains(&method_name.ident.name);
let call_to_unwrap = [sym::unwrap, sym::expect].contains(&method_name.ident.name);
if let Some(unwrappable) = self.unwrappables.iter()
.find(|u| u.local_id == id);
// Span contexts should not differ with the conditional branch
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let span_ctxt = expr.span.ctxt();
if unwrappable.branch.span.ctxt() == span_ctxt;
if unwrappable.check.span.ctxt() == span_ctxt;
then {
if call_to_unwrap == unwrappable.safe_to_unwrap {
let is_entire_condition = unwrappable.is_entire_condition;
let unwrappable_variable_name = self.cx.tcx.hir().name(unwrappable.local_id);
let suggested_pattern = if call_to_unwrap {
unwrappable.kind.success_variant_pattern()
} else {
unwrappable.kind.error_variant_pattern()
};
span_lint_hir_and_then(
self.cx,
UNNECESSARY_UNWRAP,
expr.hir_id,
expr.span,
&format!(
"called `{}` on `{}` after checking its variant with `{}`",
method_name.ident.name,
unwrappable_variable_name,
unwrappable.check_name.ident.as_str(),
),
|diag| {
if is_entire_condition {
diag.span_suggestion(
unwrappable.check.span.with_lo(unwrappable.if_expr.span.lo()),
"try",
format!(
"if let {} = {}",
suggested_pattern,
unwrappable_variable_name,
),
// We don't track how the unwrapped value is used inside the
// block or suggest deleting the unwrap, so we can't offer a
// fixable solution.
Applicability::Unspecified,
);
} else {
diag.span_label(unwrappable.check.span, "the check is happening here");
diag.help("try using `if let` or `match`");
}
},
);
} else {
span_lint_hir_and_then(
self.cx,
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PANICKING_UNWRAP,
expr.hir_id,
expr.span,
&format!("this call to `{}()` will always panic",
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method_name.ident.name),
|diag| { diag.span_label(unwrappable.check.span, "because of this check"); },
);
}
}
}
walk_expr(self, expr);
}
}
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fn nested_visit_map(&mut self) -> Self::Map {
self.cx.tcx.hir()
}
}
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declare_lint_pass!(Unwrap => [PANICKING_UNWRAP, UNNECESSARY_UNWRAP]);
impl<'tcx> LateLintPass<'tcx> for Unwrap {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
span: Span,
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fn_id: HirId,
) {
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if span.from_expansion() {
return;
}
let mut v = UnwrappableVariablesVisitor {
cx,
unwrappables: Vec::new(),
};
walk_fn(&mut v, kind, decl, body.id(), span, fn_id);
}
}