rust/clippy_lints/src/unnecessary_wraps.rs

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use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet;
use clippy_utils::{contains_return, in_macro, is_lang_ctor, return_ty, visitors::find_all_ret_expressions};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::FnKind;
use rustc_hir::LangItem::{OptionSome, ResultOk};
use rustc_hir::{Body, ExprKind, FnDecl, HirId, Impl, ItemKind, Node};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::symbol::sym;
use rustc_span::Span;
declare_clippy_lint! {
/// **What it does:** Checks for private functions that only return `Ok` or `Some`.
///
/// **Why is this bad?** It is not meaningful to wrap values when no `None` or `Err` is returned.
///
/// **Known problems:** There can be false positives if the function signature is designed to
/// fit some external requirement.
///
/// **Example:**
///
/// ```rust
/// fn get_cool_number(a: bool, b: bool) -> Option<i32> {
/// if a && b {
/// return Some(50);
/// }
/// if a {
/// Some(0)
/// } else {
/// Some(10)
/// }
/// }
/// ```
/// Use instead:
/// ```rust
/// fn get_cool_number(a: bool, b: bool) -> i32 {
/// if a && b {
/// return 50;
/// }
/// if a {
/// 0
/// } else {
/// 10
/// }
/// }
/// ```
pub UNNECESSARY_WRAPS,
pedantic,
"functions that only return `Ok` or `Some`"
}
declare_lint_pass!(UnnecessaryWraps => [UNNECESSARY_WRAPS]);
impl<'tcx> LateLintPass<'tcx> for UnnecessaryWraps {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
fn_kind: FnKind<'tcx>,
fn_decl: &FnDecl<'tcx>,
body: &Body<'tcx>,
span: Span,
hir_id: HirId,
) {
// Abort if public function/method or closure.
match fn_kind {
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FnKind::ItemFn(.., visibility) | FnKind::Method(.., Some(visibility)) => {
if visibility.node.is_pub() {
return;
}
},
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FnKind::Closure => return,
FnKind::Method(..) => (),
}
// Abort if the method is implementing a trait or of it a trait method.
if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
if matches!(
item.kind,
ItemKind::Impl(Impl { of_trait: Some(_), .. }) | ItemKind::Trait(..)
) {
return;
}
}
// Get the wrapper and inner types, if can't, abort.
let (return_type_label, lang_item, inner_type) = if let ty::Adt(adt_def, subst) = return_ty(cx, hir_id).kind() {
if cx.tcx.is_diagnostic_item(sym::option_type, adt_def.did) {
("Option", OptionSome, subst.type_at(0))
} else if cx.tcx.is_diagnostic_item(sym::result_type, adt_def.did) {
("Result", ResultOk, subst.type_at(0))
} else {
return;
}
} else {
return;
};
// Check if all return expression respect the following condition and collect them.
let mut suggs = Vec::new();
let can_sugg = find_all_ret_expressions(cx, &body.value, |ret_expr| {
if_chain! {
if !in_macro(ret_expr.span);
// Check if a function call.
if let ExprKind::Call(func, [arg]) = ret_expr.kind;
// Check if OPTION_SOME or RESULT_OK, depending on return type.
if let ExprKind::Path(qpath) = &func.kind;
if is_lang_ctor(cx, qpath, lang_item);
// Make sure the function argument does not contain a return expression.
if !contains_return(arg);
then {
suggs.push(
(
ret_expr.span,
if inner_type.is_unit() {
"".to_string()
} else {
snippet(cx, arg.span.source_callsite(), "..").to_string()
}
)
);
true
} else {
false
}
}
});
if can_sugg && !suggs.is_empty() {
let (lint_msg, return_type_sugg_msg, return_type_sugg, body_sugg_msg) = if inner_type.is_unit() {
(
"this function's return value is unnecessary".to_string(),
"remove the return type...".to_string(),
snippet(cx, fn_decl.output.span(), "..").to_string(),
"...and then remove returned values",
)
} else {
(
format!(
"this function's return value is unnecessarily wrapped by `{}`",
return_type_label
),
format!("remove `{}` from the return type...", return_type_label),
inner_type.to_string(),
"...and then change returning expressions",
)
};
span_lint_and_then(cx, UNNECESSARY_WRAPS, span, lint_msg.as_str(), |diag| {
diag.span_suggestion(
fn_decl.output.span(),
return_type_sugg_msg.as_str(),
return_type_sugg,
Applicability::MaybeIncorrect,
);
diag.multipart_suggestion(body_sugg_msg, suggs, Applicability::MaybeIncorrect);
});
}
}
}