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lint on single match expressions with a value in the else path

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Oliver 'ker' Schneider 2016-01-24 12:24:16 +01:00 • committed by Oliver Schneider
parent 5a61a95d31
commit d6c0435c81
4 changed files with 85 additions and 17 deletions
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1
src/lib.rs
View file

@ -149,6 +149,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
reg.register_lint_group("clippy_pedantic", vec![
matches::SINGLE_MATCH_ELSE,
methods::OPTION_UNWRAP_USED,
methods::RESULT_UNWRAP_USED,
methods::WRONG_PUB_SELF_CONVENTION,

76
src/matches.rs
View file

@ -28,6 +28,23 @@ declare_lint!(pub SINGLE_MATCH, Warn,
"a match statement with a single nontrivial arm (i.e, where the other arm \
is `_ => {}`) is used; recommends `if let` instead");
/// **What it does:** This lint checks for matches with a two arms where an `if let` will usually suffice. It is `Allow` by default.
///
/// **Why is this bad?** Just readability – `if let` nests less than a `match`.
///
/// **Known problems:** Personal style preferences may differ
///
/// **Example:**
/// ```
/// match x {
/// Some(ref foo) -> bar(foo),
/// _ => bar(other_ref),
/// }
/// ```
declare_lint!(pub SINGLE_MATCH_ELSE, Allow,
"a match statement with a two arms where the second arm's pattern is a wildcard; \
recommends `if let` instead");
/// **What it does:** This lint checks for matches where all arms match a reference, suggesting to remove the reference and deref the matched expression instead. It also checks for `if let &foo = bar` blocks. It is `Warn` by default.
///
/// **Why is this bad?** It just makes the code less readable. That reference destructuring adds nothing to the code.
@ -89,7 +106,7 @@ pub struct MatchPass;
impl LintPass for MatchPass {
fn get_lints(&self) -> LintArray {
lint_array!(SINGLE_MATCH, MATCH_REF_PATS, MATCH_BOOL)
lint_array!(SINGLE_MATCH, MATCH_REF_PATS, MATCH_BOOL, SINGLE_MATCH_ELSE)
}
}
@ -112,34 +129,49 @@ impl LateLintPass for MatchPass {
fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
if arms.len() == 2 &&
arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
is_unit_expr(&arms[1].body) {
arms[1].pats.len() == 1 && arms[1].guard.is_none() {
let els = if is_unit_expr(&arms[1].body) {
None
} else if let ExprBlock(_) = arms[1].body.node {
// matches with blocks that contain statements are prettier as `if let + else`
Some(&*arms[1].body)
} else {
// allow match arms with just expressions
return;
};
let ty = cx.tcx.expr_ty(ex);
if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
check_single_match_single_pattern(cx, ex, arms, expr);
check_single_match_opt_like(cx, ex, arms, expr, ty);
check_single_match_single_pattern(cx, ex, arms, expr, els);
check_single_match_opt_like(cx, ex, arms, expr, ty, els);
}
}
}
fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
if arms[1].pats[0].node == PatWild {
let lint = if els.is_some() {
SINGLE_MATCH_ELSE
} else {
SINGLE_MATCH
};
let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
span_lint_and_then(cx,
SINGLE_MATCH,
lint,
expr.span,
"you seem to be trying to use match for destructuring a single pattern. \
Consider using `if let`", |db| {
db.span_suggestion(expr.span, "try this",
format!("if let {} = {} {}",
format!("if let {} = {} {}{}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."),
expr_block(cx, &arms[0].body, None, "..")));
expr_block(cx, &arms[0].body, None, ".."),
els_str));
});
}
}
fn check_single_match_opt_like(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, ty: ty::Ty) {
// list of candidate Enums we know will never get any more membre
fn check_single_match_opt_like(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, ty: ty::Ty, els: Option<&Expr>) {
// list of candidate Enums we know will never get any more members
let candidates = &[
(&COW_PATH, "Borrowed"),
(&COW_PATH, "Cow::Borrowed"),
@ -151,23 +183,37 @@ fn check_single_match_opt_like(cx: &LateContext, ex: &Expr, arms: &[Arm], expr:
];
let path = match arms[1].pats[0].node {
PatEnum(ref path, _) => path.to_string(),
PatEnum(ref path, Some(ref inner)) => {
// contains any non wildcard patterns? e.g. Err(err)
if inner.iter().any(|pat| if let PatWild = pat.node { false } else { true }) {
return;
}
path.to_string()
},
PatEnum(ref path, None) => path.to_string(),
PatIdent(BindByValue(MutImmutable), ident, None) => ident.node.to_string(),
_ => return
};
for &(ty_path, pat_path) in candidates {
if &path == pat_path && match_type(cx, ty, ty_path) {
let lint = if els.is_some() {
SINGLE_MATCH_ELSE
} else {
SINGLE_MATCH
};
let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
span_lint_and_then(cx,
SINGLE_MATCH,
lint,
expr.span,
"you seem to be trying to use match for destructuring a single pattern. \
Consider using `if let`", |db| {
db.span_suggestion(expr.span, "try this",
format!("if let {} = {} {}",
format!("if let {} = {} {}{}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."),
expr_block(cx, &arms[0].body, None, "..")));
expr_block(cx, &arms[0].body, None, ".."),
els_str));
});
}
}