rust/src/misc_early.rs

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use rustc::lint::*;
use std::collections::HashMap;
use syntax::ast::*;
use syntax::codemap::Span;
use syntax::visit::FnKind;
use utils::{span_lint, span_help_and_lint, snippet, span_lint_and_then};
/// **What it does:** This lint checks for structure field patterns bound to wildcards.
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///
/// **Why is this bad?** Using `..` instead is shorter and leaves the focus on the fields that are actually bound.
///
/// **Known problems:** None.
///
/// **Example:** `let { a: _, b: ref b, c: _ } = ..`
declare_lint! {
pub UNNEEDED_FIELD_PATTERN, Warn,
"Struct fields are bound to a wildcard instead of using `..`"
}
/// **What it does:** This lint checks for function arguments having the similar names differing by an underscore
///
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/// **Why is this bad?** It affects code readability
///
/// **Known problems:** None.
///
/// **Example:** `fn foo(a: i32, _a: i32) {}`
declare_lint! {
pub DUPLICATE_UNDERSCORE_ARGUMENT, Warn,
"Function arguments having names which only differ by an underscore"
}
/// **What it does:** This lint detects closures called in the same expression where they are defined.
///
/// **Why is this bad?** It is unnecessarily adding to the expression's complexity.
///
/// **Known problems:** None.
///
/// **Example:** `(|| 42)()`
declare_lint! {
pub REDUNDANT_CLOSURE_CALL, Warn,
"Closures should not be called in the expression they are defined"
}
#[derive(Copy, Clone)]
pub struct MiscEarly;
impl LintPass for MiscEarly {
fn get_lints(&self) -> LintArray {
lint_array!(UNNEEDED_FIELD_PATTERN, DUPLICATE_UNDERSCORE_ARGUMENT, REDUNDANT_CLOSURE_CALL)
}
}
impl EarlyLintPass for MiscEarly {
fn check_pat(&mut self, cx: &EarlyContext, pat: &Pat) {
if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
let mut wilds = 0;
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let type_name = npat.segments.last().expect("A path must have at least one segment").identifier.name;
for field in pfields {
if field.node.pat.node == PatKind::Wild {
wilds += 1;
}
}
if !pfields.is_empty() && wilds == pfields.len() {
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span_help_and_lint(cx,
UNNEEDED_FIELD_PATTERN,
pat.span,
"All the struct fields are matched to a wildcard pattern, consider using `..`.",
&format!("Try with `{} {{ .. }}` instead", type_name));
return;
}
if wilds > 0 {
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let mut normal = vec![];
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for field in pfields {
if field.node.pat.node != PatKind::Wild {
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if let Ok(n) = cx.sess().codemap().span_to_snippet(field.span) {
normal.push(n);
}
}
}
for field in pfields {
if field.node.pat.node == PatKind::Wild {
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wilds -= 1;
if wilds > 0 {
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span_lint(cx,
UNNEEDED_FIELD_PATTERN,
field.span,
"You matched a field with a wildcard pattern. Consider using `..` instead");
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} else {
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span_help_and_lint(cx,
UNNEEDED_FIELD_PATTERN,
field.span,
"You matched a field with a wildcard pattern. Consider using `..` \
instead",
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&format!("Try with `{} {{ {}, .. }}`",
type_name,
normal[..].join(", ")));
}
}
}
}
}
}
fn check_fn(&mut self, cx: &EarlyContext, _: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
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let mut registered_names: HashMap<String, Span> = HashMap::new();
for ref arg in &decl.inputs {
if let PatKind::Ident(_, sp_ident, None) = arg.pat.node {
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let arg_name = sp_ident.node.to_string();
if arg_name.starts_with('_') {
if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
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span_lint(cx,
DUPLICATE_UNDERSCORE_ARGUMENT,
*correspondence,
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&format!("`{}` already exists, having another argument having almost the same \
name makes code comprehension and documentation more difficult",
arg_name[1..].to_owned()));;
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}
} else {
registered_names.insert(arg_name, arg.pat.span);
}
}
}
}
fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
if let ExprKind::Call(ref paren, _) = expr.node {
if let ExprKind::Paren(ref closure) = paren.node {
if let ExprKind::Closure(_, ref decl, ref block) = closure.node {
span_lint_and_then(cx,
REDUNDANT_CLOSURE_CALL,
expr.span,
"Try not to call a closure in the expression where it is declared.",
|db| {
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if decl.inputs.is_empty() {
let hint = format!("{}", snippet(cx, block.span, ".."));
db.span_suggestion(expr.span, "Try doing something like: ", hint);
}
});
}
}
}
}
fn check_block(&mut self, cx: &EarlyContext, block: &Block) {
for w in block.stmts.windows(2) {
if_let_chain! {[
let StmtKind::Decl(ref first, _) = w[0].node,
let DeclKind::Local(ref local) = first.node,
let Option::Some(ref t) = local.init,
let ExprKind::Closure(_,_,_) = t.node,
let PatKind::Ident(_,sp_ident,_) = local.pat.node,
let StmtKind::Semi(ref second,_) = w[1].node,
let ExprKind::Assign(_,ref call) = second.node,
let ExprKind::Call(ref closure,_) = call.node,
let ExprKind::Path(_,ref path) = closure.node
], {
if sp_ident.node == (&path.segments[0]).identifier {
span_lint(cx, REDUNDANT_CLOSURE_CALL, second.span, "Closure called just once immediately after it was declared");
}
}}
}
}
}