rust-clippy/clippy_lints/src/redundant_pattern_matching.rs

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use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
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use rustc::declare_lint_pass;
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc_errors::Applicability;
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use rustc_session::declare_tool_lint;
use syntax::ast::LitKind;
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declare_clippy_lint! {
/// **What it does:** Lint for redundant pattern matching over `Result` or
/// `Option`
///
/// **Why is this bad?** It's more concise and clear to just use the proper
/// utility function
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// if let Ok(_) = Ok::<i32, i32>(42) {}
/// if let Err(_) = Err::<i32, i32>(42) {}
/// if let None = None::<()> {}
/// if let Some(_) = Some(42) {}
/// match Ok::<i32, i32>(42) {
/// Ok(_) => true,
/// Err(_) => false,
/// };
/// ```
///
/// The more idiomatic use would be:
///
/// ```rust
/// if Ok::<i32, i32>(42).is_ok() {}
/// if Err::<i32, i32>(42).is_err() {}
/// if None::<()>.is_none() {}
/// if Some(42).is_some() {}
/// Ok::<i32, i32>(42).is_ok();
/// ```
pub REDUNDANT_PATTERN_MATCHING,
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style,
"use the proper utility function avoiding an `if let`"
}
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declare_lint_pass!(RedundantPatternMatching => [REDUNDANT_PATTERN_MATCHING]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantPatternMatching {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Match(op, arms, ref match_source) = &expr.kind {
match match_source {
MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
MatchSource::IfLetDesugar { contains_else_clause } => {
find_sugg_for_if_let(cx, expr, op, arms, *contains_else_clause)
},
_ => return,
}
}
}
}
fn find_sugg_for_if_let<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
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expr: &'tcx Expr<'_>,
op: &Expr<'_>,
arms: &[Arm<'_>],
has_else: bool,
) {
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let good_method = match arms[0].pat.kind {
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PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
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if let PatKind::Wild = patterns[0].kind {
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if match_qpath(path, &paths::RESULT_OK) {
"is_ok()"
} else if match_qpath(path, &paths::RESULT_ERR) {
"is_err()"
} else if match_qpath(path, &paths::OPTION_SOME) {
"is_some()"
} else {
return;
}
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} else {
return;
}
},
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PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
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_ => return,
};
let maybe_semi = if has_else { "" } else { ";" };
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span_lint_and_then(
cx,
REDUNDANT_PATTERN_MATCHING,
arms[0].pat.span,
&format!("redundant pattern matching, consider using `{}`", good_method),
|db| {
let span = expr.span.to(op.span);
db.span_suggestion(
span,
"try this",
format!("{}.{}{}", snippet(cx, op.span, "_"), good_method, maybe_semi),
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Applicability::MaybeIncorrect, // snippet
);
},
);
}
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fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, op: &Expr<'_>, arms: &[Arm<'_>]) {
if arms.len() == 2 {
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let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
let found_good_method = match node_pair {
(
PatKind::TupleStruct(ref path_left, ref patterns_left, _),
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PatKind::TupleStruct(ref path_right, ref patterns_right, _),
) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
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if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].kind, &patterns_right[0].kind) {
find_good_method_for_match(
arms,
path_left,
path_right,
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&paths::RESULT_OK,
&paths::RESULT_ERR,
"is_ok()",
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"is_err()",
)
} else {
None
}
},
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(PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
| (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
if patterns.len() == 1 =>
{
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if let PatKind::Wild = patterns[0].kind {
find_good_method_for_match(
arms,
path_left,
path_right,
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&paths::OPTION_SOME,
&paths::OPTION_NONE,
"is_some()",
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"is_none()",
)
} else {
None
}
},
_ => None,
};
if let Some(good_method) = found_good_method {
span_lint_and_then(
cx,
REDUNDANT_PATTERN_MATCHING,
expr.span,
&format!("redundant pattern matching, consider using `{}`", good_method),
|db| {
let span = expr.span.to(op.span);
db.span_suggestion(
span,
"try this",
format!("{}.{}", snippet(cx, op.span, "_"), good_method),
Applicability::MaybeIncorrect, // snippet
);
},
);
}
}
}
fn find_good_method_for_match<'a>(
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arms: &[Arm<'_>],
path_left: &QPath,
path_right: &QPath,
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expected_left: &[&str],
expected_right: &[&str],
should_be_left: &'a str,
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should_be_right: &'a str,
) -> Option<&'a str> {
let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
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(&(*arms[0].body).kind, &(*arms[1].body).kind)
} else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
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(&(*arms[1].body).kind, &(*arms[0].body).kind)
} else {
return None;
};
match body_node_pair {
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(ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
(LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
(LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
_ => None,
},
_ => None,
}
}