bjoernager/rust
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matches: new module, move single_match lint there

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This commit is contained in:
Georg Brandl 2015-08-21 19:32:21 +02:00
parent 371584a637
commit 5403e82681
3 changed files with 65 additions and 64 deletions
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5
src/lib.rs
View file

@ -38,11 +38,11 @@ pub mod returns;
pub mod lifetimes;
pub mod loops;
pub mod ranges;
pub mod matches;
#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
reg.register_lint_pass(box types::TypePass as LintPassObject);
reg.register_lint_pass(box misc::MiscPass as LintPassObject);
reg.register_lint_pass(box misc::TopLevelRefPass as LintPassObject);
reg.register_lint_pass(box misc::CmpNan as LintPassObject);
reg.register_lint_pass(box eq_op::EqOp as LintPassObject);
@ -71,6 +71,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
reg.register_lint_pass(box ranges::StepByZero as LintPassObject);
reg.register_lint_pass(box types::CastPass as LintPassObject);
reg.register_lint_pass(box types::TypeComplexityPass as LintPassObject);
reg.register_lint_pass(box matches::MatchPass as LintPassObject);
reg.register_lint_group("clippy", vec![
approx_const::APPROX_CONSTANT,
@ -87,6 +88,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
loops::EXPLICIT_ITER_LOOP,
loops::ITER_NEXT_LOOP,
loops::NEEDLESS_RANGE_LOOP,
matches::SINGLE_MATCH,
methods::OPTION_UNWRAP_USED,
methods::RESULT_UNWRAP_USED,
methods::STR_TO_STRING,
@ -96,7 +98,6 @@ pub fn plugin_registrar(reg: &mut Registry) {
misc::FLOAT_CMP,
misc::MODULO_ONE,
misc::PRECEDENCE,
misc::SINGLE_MATCH,
misc::TOPLEVEL_REF_ARG,
mut_mut::MUT_MUT,
needless_bool::NEEDLESS_BOOL,

61
src/matches.rs Normal file
View file

@ -0,0 +1,61 @@
use rustc::lint::*;
use syntax::ast;
use syntax::ast::*;
use std::borrow::Cow;
use utils::{snippet, snippet_block, span_help_and_lint};
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");
#[allow(missing_copy_implementations)]
pub struct MatchPass;
impl LintPass for MatchPass {
fn get_lints(&self) -> LintArray {
lint_array!(SINGLE_MATCH)
}
fn check_expr(&mut self, cx: &Context, expr: &Expr) {
if let ExprMatch(ref ex, ref arms, ast::MatchSource::Normal) = expr.node {
// check preconditions: only two arms
if arms.len() == 2 &&
// both of the arms have a single pattern and no guard
arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
// and the second pattern is a `_` wildcard: this is not strictly necessary,
// since the exhaustiveness check will ensure the last one is a catch-all,
// but in some cases, an explicit match is preferred to catch situations
// when an enum is extended, so we don't consider these cases
arms[1].pats[0].node == PatWild(PatWildSingle) &&
// finally, we don't want any content in the second arm (unit or empty block)
is_unit_expr(&*arms[1].body)
{
let body_code = snippet_block(cx, arms[0].body.span, "..");
let body_code = if let ExprBlock(_) = arms[0].body.node {
body_code
} else {
Cow::Owned(format!("{{ {} }}", body_code))
};
span_help_and_lint(cx, SINGLE_MATCH, expr.span,
"you seem to be trying to use match for \
destructuring a single pattern. Did you mean to \
use `if let`?",
&*format!("try\nif let {} = {} {}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."),
body_code)
);
}
}
}
}
fn is_unit_expr(expr: &Expr) -> bool {
match expr.node {
ExprTup(ref v) if v.is_empty() => true,
ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
_ => false,
}
}

63
src/misc.rs
View file

@ -1,75 +1,14 @@
use rustc::lint::*;
use syntax::ptr::P;
use syntax::ast;
use syntax::ast::*;
use syntax::ast_util::{is_comparison_binop, binop_to_string};
use syntax::codemap::{Span, Spanned};
use syntax::visit::FnKind;
use rustc::middle::ty;
use std::borrow::Cow;
use utils::{match_path, snippet, snippet_block, span_lint, span_help_and_lint, walk_ptrs_ty};
use utils::{match_path, snippet, span_lint, walk_ptrs_ty};
use consts::constant;
/// Handles uncategorized lints
/// Currently handles linting of if-let-able matches
#[allow(missing_copy_implementations)]
pub struct MiscPass;
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");
impl LintPass for MiscPass {
fn get_lints(&self) -> LintArray {
lint_array!(SINGLE_MATCH)
}
fn check_expr(&mut self, cx: &Context, expr: &Expr) {
if let ExprMatch(ref ex, ref arms, ast::MatchSource::Normal) = expr.node {
// check preconditions: only two arms
if arms.len() == 2 &&
// both of the arms have a single pattern and no guard
arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
// and the second pattern is a `_` wildcard: this is not strictly necessary,
// since the exhaustiveness check will ensure the last one is a catch-all,
// but in some cases, an explicit match is preferred to catch situations
// when an enum is extended, so we don't consider these cases
arms[1].pats[0].node == PatWild(PatWildSingle) &&
// finally, we don't want any content in the second arm (unit or empty block)
is_unit_expr(&*arms[1].body)
{
let body_code = snippet_block(cx, arms[0].body.span, "..");
let body_code = if let ExprBlock(_) = arms[0].body.node {
body_code
} else {
Cow::Owned(format!("{{ {} }}", body_code))
};
span_help_and_lint(cx, SINGLE_MATCH, expr.span,
"you seem to be trying to use match for \
destructuring a single pattern. Did you mean to \
use `if let`?",
&*format!("try\nif let {} = {} {}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."),
body_code)
);
}
}
}
}
fn is_unit_expr(expr: &Expr) -> bool {
match expr.node {
ExprTup(ref v) if v.is_empty() => true,
ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
_ => false,
}
}
declare_lint!(pub TOPLEVEL_REF_ARG, Warn,
"a function argument is declared `ref` (i.e. `fn foo(ref x: u8)`, but not \
`fn foo((ref x, ref y): (u8, u8))`)");