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|
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet;
use clippy_utils::{path_to_local_id, visitors::is_local_used};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_hir::BindingAnnotation;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for variable declarations immediately followed by a
/// conditional affectation.
///
/// ### Why is this bad?
/// This is not idiomatic Rust.
///
/// ### Example
/// ```rust,ignore
/// let foo;
///
/// if bar() {
/// foo = 42;
/// } else {
/// foo = 0;
/// }
///
/// let mut baz = None;
///
/// if bar() {
/// baz = Some(42);
/// }
/// ```
///
/// should be written
///
/// ```rust,ignore
/// let foo = if bar() {
/// 42
/// } else {
/// 0
/// };
///
/// let baz = if bar() {
/// Some(42)
/// } else {
/// None
/// };
/// ```
#[clippy::version = "pre 1.29.0"]
pub USELESS_LET_IF_SEQ,
nursery,
"unidiomatic `let mut` declaration followed by initialization in `if`"
}
declare_lint_pass!(LetIfSeq => [USELESS_LET_IF_SEQ]);
impl<'tcx> LateLintPass<'tcx> for LetIfSeq {
fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
let mut it = block.stmts.iter().peekable();
while let Some(stmt) = it.next() {
if_chain! {
if let Some(expr) = it.peek();
if let hir::StmtKind::Local(local) = stmt.kind;
if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.kind;
if let hir::StmtKind::Expr(if_) = expr.kind;
if let hir::ExprKind::If(hir::Expr { kind: hir::ExprKind::DropTemps(cond), ..}, then, else_) = if_.kind;
if !is_local_used(cx, *cond, canonical_id);
if let hir::ExprKind::Block(then, _) = then.kind;
if let Some(value) = check_assign(cx, canonical_id, then);
if !is_local_used(cx, value, canonical_id);
then {
let span = stmt.span.to(if_.span);
let has_interior_mutability = !cx.typeck_results().node_type(canonical_id).is_freeze(
cx.tcx.at(span),
cx.param_env,
);
if has_interior_mutability { return; }
let (default_multi_stmts, default) = if let Some(else_) = else_ {
if let hir::ExprKind::Block(else_, _) = else_.kind {
if let Some(default) = check_assign(cx, canonical_id, else_) {
(else_.stmts.len() > 1, default)
} else if let Some(default) = local.init {
(true, default)
} else {
continue;
}
} else {
continue;
}
} else if let Some(default) = local.init {
(false, default)
} else {
continue;
};
let mutability = match mode {
BindingAnnotation::RefMut | BindingAnnotation::Mutable => "<mut> ",
_ => "",
};
// FIXME: this should not suggest `mut` if we can detect that the variable is not
// use mutably after the `if`
let sug = format!(
"let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
mut=mutability,
name=ident.name,
cond=snippet(cx, cond.span, "_"),
then=if then.stmts.len() > 1 { " ..;" } else { "" },
else=if default_multi_stmts { " ..;" } else { "" },
value=snippet(cx, value.span, "<value>"),
default=snippet(cx, default.span, "<default>"),
);
span_lint_and_then(cx,
USELESS_LET_IF_SEQ,
span,
"`if _ { .. } else { .. }` is an expression",
|diag| {
diag.span_suggestion(
span,
"it is more idiomatic to write",
sug,
Applicability::HasPlaceholders,
);
if !mutability.is_empty() {
diag.note("you might not need `mut` at all");
}
});
}
}
}
}
}
fn check_assign<'tcx>(
cx: &LateContext<'tcx>,
decl: hir::HirId,
block: &'tcx hir::Block<'_>,
) -> Option<&'tcx hir::Expr<'tcx>> {
if_chain! {
if block.expr.is_none();
if let Some(expr) = block.stmts.iter().last();
if let hir::StmtKind::Semi(expr) = expr.kind;
if let hir::ExprKind::Assign(var, value, _) = expr.kind;
if path_to_local_id(var, decl);
then {
if block.stmts.iter().take(block.stmts.len()-1).any(|stmt| is_local_used(cx, stmt, decl)) {
None
} else {
Some(value)
}
} else {
None
}
}
}
|
