157 lines
4.1 KiB
Rust
157 lines
4.1 KiB
Rust
//! Checks for if expressions that contain only an if expression.
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//!
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//! For example, the lint would catch:
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//!
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//! ```rust,ignore
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//! if x {
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//! if y {
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//! println!("Hello world");
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//! }
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//! }
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//! ```
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//!
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//! This lint is **warn** by default
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use rustc::lint::*;
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use syntax::ast;
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use utils::{in_macro, snippet_block, span_lint_and_sugg, span_lint_and_then};
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use utils::sugg::Sugg;
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/// **What it does:** Checks for nested `if` statements which can be collapsed
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/// by `&&`-combining their conditions and for `else { if ... }` expressions
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/// that
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/// can be collapsed to `else if ...`.
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///
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/// **Why is this bad?** Each `if`-statement adds one level of nesting, which
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/// makes code look more complex than it really is.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust,ignore
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/// if x {
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/// if y {
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/// …
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/// }
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/// }
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///
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/// // or
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///
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/// if x {
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/// …
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/// } else {
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/// if y {
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/// …
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/// }
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/// }
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/// ```
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///
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/// Should be written:
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///
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/// ```rust.ignore
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/// if x && y {
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/// …
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/// }
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///
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/// // or
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///
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/// if x {
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/// …
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/// } else if y {
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/// …
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/// }
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/// ```
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declare_lint! {
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pub COLLAPSIBLE_IF,
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Warn,
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"`if`s that can be collapsed (e.g. `if x { if y { ... } }` and `else { if x { ... } }`)"
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}
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#[derive(Copy, Clone)]
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pub struct CollapsibleIf;
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impl LintPass for CollapsibleIf {
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fn get_lints(&self) -> LintArray {
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lint_array!(COLLAPSIBLE_IF)
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}
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}
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impl EarlyLintPass for CollapsibleIf {
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fn check_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr) {
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if !in_macro(expr.span) {
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check_if(cx, expr)
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}
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}
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}
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fn check_if(cx: &EarlyContext, expr: &ast::Expr) {
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match expr.node {
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ast::ExprKind::If(ref check, ref then, ref else_) => if let Some(ref else_) = *else_ {
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check_collapsible_maybe_if_let(cx, else_);
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} else {
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check_collapsible_no_if_let(cx, expr, check, then);
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},
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ast::ExprKind::IfLet(_, _, _, Some(ref else_)) => {
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check_collapsible_maybe_if_let(cx, else_);
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},
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_ => (),
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}
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}
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fn check_collapsible_maybe_if_let(cx: &EarlyContext, else_: &ast::Expr) {
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if_chain! {
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if let ast::ExprKind::Block(ref block) = else_.node;
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if let Some(else_) = expr_block(block);
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if !in_macro(else_.span);
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then {
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match else_.node {
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ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => {
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span_lint_and_sugg(cx,
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COLLAPSIBLE_IF,
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block.span,
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"this `else { if .. }` block can be collapsed",
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"try",
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snippet_block(cx, else_.span, "..").into_owned());
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}
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_ => (),
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}
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}
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}
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}
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fn check_collapsible_no_if_let(cx: &EarlyContext, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
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if_chain! {
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if let Some(inner) = expr_block(then);
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if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node;
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then {
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if expr.span.ctxt() != inner.span.ctxt() {
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return;
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}
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span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
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let lhs = Sugg::ast(cx, check, "..");
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let rhs = Sugg::ast(cx, check_inner, "..");
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db.span_suggestion(expr.span,
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"try",
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format!("if {} {}",
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lhs.and(&rhs),
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snippet_block(cx, content.span, "..")));
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});
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}
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}
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}
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/// If the block contains only one expression, return it.
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fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
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let mut it = block.stmts.iter();
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if let (Some(stmt), None) = (it.next(), it.next()) {
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match stmt.node {
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ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),
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_ => None,
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}
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} else {
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None
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}
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}
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