76 lines
2.5 KiB
Rust
76 lines
2.5 KiB
Rust
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use syntax::ast;
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use syntax::ast::*;
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use syntax::codemap::Span;
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use syntax::visit::FnKind;
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use rustc::lint::{Context, LintPass, LintArray};
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use utils::{span_lint, snippet};
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declare_lint!(pub NEEDLESS_RETURN, Warn,
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"Warn on using a return statement where an expression would be enough");
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#[derive(Copy,Clone)]
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pub struct ReturnPass;
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impl ReturnPass {
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// Check the final stmt or expr in a block for unnecessary return.
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fn check_block_return(&mut self, cx: &Context, block: &Block) {
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if let Some(ref expr) = block.expr {
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self.check_final_expr(cx, expr);
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} else if let Some(stmt) = block.stmts.last() {
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if let StmtSemi(ref expr, _) = stmt.node {
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if let ExprRet(Some(ref inner)) = expr.node {
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self.emit_lint(cx, (expr.span, inner.span));
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}
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}
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}
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}
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// Check a the final expression in a block if it's a return.
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fn check_final_expr(&mut self, cx: &Context, expr: &Expr) {
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match expr.node {
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// simple return is always "bad"
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ExprRet(Some(ref inner)) => {
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self.emit_lint(cx, (expr.span, inner.span));
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}
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// a whole block? check it!
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ExprBlock(ref block) => {
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self.check_block_return(cx, block);
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}
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// an if/if let expr, check both exprs
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// note, if without else is going to be a type checking error anyways
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// (except for unit type functions) so we don't match it
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ExprIf(_, ref ifblock, Some(ref elsexpr)) |
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ExprIfLet(_, _, ref ifblock, Some(ref elsexpr)) => {
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self.check_block_return(cx, ifblock);
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self.check_final_expr(cx, elsexpr);
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}
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// a match expr, check all arms
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ExprMatch(_, ref arms, _) => {
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for arm in arms {
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self.check_final_expr(cx, &*arm.body);
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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 emit_lint(&mut self, cx: &Context, spans: (Span, Span)) {
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span_lint(cx, NEEDLESS_RETURN, spans.0, &format!(
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"unneeded return statement. Consider using {} \
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without the trailing semicolon",
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snippet(cx, spans.1, "..")))
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}
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}
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impl LintPass for ReturnPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_RETURN)
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}
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fn check_fn(&mut self, cx: &Context, _: FnKind, _: &FnDecl,
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block: &Block, _: Span, _: ast::NodeId) {
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self.check_block_return(cx, block);
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}
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}
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