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use rustc::lint::*;
use rustc::hir::*;
use syntax::codemap::Span;
use utils::{paths, span_lint_and_then, match_path, snippet};
/// **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) {}
/// ```
///
/// 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() {}
/// ```
///
declare_lint! {
pub IF_LET_REDUNDANT_PATTERN_MATCHING,
Warn,
"use the proper utility function avoiding an `if let`"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(IF_LET_REDUNDANT_PATTERN_MATCHING)
}
}
impl LateLintPass for Pass {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if let ExprMatch(ref op, ref arms, MatchSource::IfLetDesugar{..}) = expr.node {
if arms[0].pats.len() == 1 {
let good_method = match arms[0].pats[0].node {
PatKind::TupleStruct(ref path, ref pats, _) if pats.len() == 1 && pats[0].node == PatKind::Wild => {
if match_path(path, &paths::RESULT_OK) {
"is_ok()"
} else if match_path(path, &paths::RESULT_ERR) {
"is_err()"
} else if match_path(path, &paths::OPTION_SOME) {
"is_some()"
} else {
return
}
}
PatKind::Path(_, ref path) if match_path(path, &paths::OPTION_NONE) => {
"is_none()"
}
_ => return
};
span_lint_and_then(cx,
IF_LET_REDUNDANT_PATTERN_MATCHING,
arms[0].pats[0].span,
&format!("redundant pattern matching, consider using `{}`", good_method),
|db| {
let span = Span {
lo: expr.span.lo,
hi: op.span.hi,
expn_id: expr.span.expn_id,
};
db.span_suggestion(span,
"try this",
format!("if {}.{}", snippet(cx, op.span, "_"), good_method));
});
}
}
}
}