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Auto merge of rust-lang#7584 - shepmaster:unnecessary_expect, r=camst…
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…effen

Extend unnecessary_unwrap to look for expect in addition to unwrap

changelog: Extend ``[`unnecessary_unwrap`]`` to also check for `Option::expect` and `Result::expect`. Also give code suggestions in some cases.

Fixes rust-lang#7581
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@bors
bors committed Sep 4, 2021
2 parents a8c2c7b b477543 commit f771927
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Showing 6 changed files with 212 additions and 69 deletions.
133 changes: 111 additions & 22 deletions clippy_lints/src/unwrap.rs
View file
Original file line number Diff line number Diff line change
@@ -1,10 1,11 @@
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::higher;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::{differing_macro_contexts, usage::is_potentially_mutated};
use clippy_utils::{differing_macro_contexts, path_to_local, usage::is_potentially_mutated};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, Path, QPath, UnOp};
use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, PathSegment, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_middle::lint::in_external_macro;
Expand Down Expand Up @@ -74,26 75,61 @@ 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
ident: &'tcx Path<'tcx>,
local_id: HirId,
/// The if itself
if_expr: &'tcx Expr<'tcx>,
/// The check, like `x.is_ok()`
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<'_>,
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 {
is_type_diagnostic_item(cx, ty, sym::option_type) && ["is_some", "is_none"].contains(&method_name)
Expand All @@ -106,18 142,18 @@ fn collect_unwrap_info<'tcx>(
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, left, branch, invert);
unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
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, expr, branch, !invert);
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 ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
if let Some(local_id) = path_to_local(&args[0]);
let ty = cx.typeck_results().expr_ty(&args[0]);
let name = method_name.ident.as_str();
if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
Expand All @@ -129,19 165,42 @@ fn collect_unwrap_info<'tcx>(
_ => unreachable!(),
};
let safe_to_unwrap = unwrappable != invert;
return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
let kind = if is_type_diagnostic_item(cx, ty, sym::option_type) {
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, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
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, cond, branch, else_branch) {
if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
|| is_potentially_mutated(unwrap_info.ident, branch, self.cx)
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;
Expand All @@ -163,32 222,62 @@ impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
}
if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr) {
walk_expr(self, cond);
self.visit_branch(cond, then, false);
self.visit_branch(expr, cond, then, false);
if let Some(else_inner) = r#else {
self.visit_branch(cond, else_inner, true);
self.visit_branch(expr, cond, else_inner, true);
}
} else {
// find `unwrap[_err]()` calls:
if_chain! {
if let ExprKind::MethodCall(method_name, _, args, _) = expr.kind;
if let ExprKind::Path(QPath::Resolved(None, path)) = args[0].kind;
if [sym::unwrap, sym!(unwrap_err)].contains(&method_name.ident.name);
let call_to_unwrap = method_name.ident.name == sym::unwrap;
if let Some(id) = path_to_local(&args[0]);
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.ident.res == path.res);
.find(|u| u.local_id == id);
// Span contexts should not differ with the conditional branch
if !differing_macro_contexts(unwrappable.branch.span, expr.span);
if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
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_and_then(
self.cx,
UNNECESSARY_UNWRAP,
expr.span,
&format!("you checked before that `{}()` cannot fail, \
instead of checking and unwrapping, it's better to use `if let` or `match`",
method_name.ident.name),
|diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
&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_and_then(
Expand Down
11 changes: 3 additions & 8 deletions clippy_utils/src/usage.rs
View file
Original file line number Diff line number Diff line change
@@ -1,10 1,9 @@
use crate as utils;
use rustc_hir as hir;
use rustc_hir::def::Res;
use rustc_hir::intravisit;
use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
use rustc_hir::HirIdSet;
use rustc_hir::{Expr, ExprKind, HirId, Path};
use rustc_hir::{Expr, ExprKind, HirId};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
Expand Down Expand Up @@ -35,12 34,8 @@ pub fn mutated_variables<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) ->
Some(delegate.used_mutably)
}

pub fn is_potentially_mutated<'tcx>(variable: &'tcx Path<'_>, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
if let Res::Local(id) = variable.res {
mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&id))
} else {
true
}
pub fn is_potentially_mutated<'tcx>(variable: HirId, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&variable))
}

struct MutVarsDelegate {
Expand Down
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