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//! Lint on if expressions with an else if, but without a final else branch.
use clippy_utils::diagnostics::span_lint_and_help;
use rustc_ast::ast::{Expr, ExprKind};
use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for usage of if expressions with an `else if` branch,
/// but without a final `else` branch.
///
/// **Why is this bad?** Some coding guidelines require this (e.g., MISRA-C:2004 Rule 14.10).
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # fn a() {}
/// # fn b() {}
/// # let x: i32 = 1;
/// if x.is_positive() {
/// a();
/// } else if x.is_negative() {
/// b();
/// }
/// ```
///
/// Could be written:
///
/// ```rust
/// # fn a() {}
/// # fn b() {}
/// # let x: i32 = 1;
/// if x.is_positive() {
/// a();
/// } else if x.is_negative() {
/// b();
/// } else {
/// // We don't care about zero.
/// }
/// ```
pub ELSE_IF_WITHOUT_ELSE,
restriction,
"`if` expression with an `else if`, but without a final `else` branch"
}
declare_lint_pass!(ElseIfWithoutElse => [ELSE_IF_WITHOUT_ELSE]);
impl EarlyLintPass for ElseIfWithoutElse {
fn check_expr(&mut self, cx: &EarlyContext<'_>, mut item: &Expr) {
if in_external_macro(cx.sess(), item.span) {
return;
}
while let ExprKind::If(_, _, Some(ref els)) = item.kind {
if let ExprKind::If(_, _, None) = els.kind {
span_lint_and_help(
cx,
ELSE_IF_WITHOUT_ELSE,
els.span,
"`if` expression with an `else if`, but without a final `else`",
None,
"add an `else` block here",
);
}
item = els;
}
}
}
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