271 lines
9.9 KiB
Rust
271 lines
9.9 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::{snippet, snippet_with_applicability, snippet_with_context};
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use clippy_utils::ty::is_type_diagnostic_item;
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use clippy_utils::{iter_input_pats, method_chain_args};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir as hir;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, Ty};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for usage of `option.map(f)` where f is a function
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/// or closure that returns the unit type `()`.
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///
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/// ### Why is this bad?
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/// Readability, this can be written more clearly with
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/// an if let statement
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///
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/// ### Example
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/// ```rust
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/// # fn do_stuff() -> Option<String> { Some(String::new()) }
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/// # fn log_err_msg(foo: String) -> Option<String> { Some(foo) }
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/// # fn format_msg(foo: String) -> String { String::new() }
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/// let x: Option<String> = do_stuff();
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/// x.map(log_err_msg);
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/// # let x: Option<String> = do_stuff();
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/// x.map(|msg| log_err_msg(format_msg(msg)));
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/// ```
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///
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/// The correct use would be:
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///
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/// ```rust
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/// # fn do_stuff() -> Option<String> { Some(String::new()) }
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/// # fn log_err_msg(foo: String) -> Option<String> { Some(foo) }
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/// # fn format_msg(foo: String) -> String { String::new() }
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/// let x: Option<String> = do_stuff();
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/// if let Some(msg) = x {
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/// log_err_msg(msg);
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/// }
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///
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/// # let x: Option<String> = do_stuff();
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/// if let Some(msg) = x {
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/// log_err_msg(format_msg(msg));
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/// }
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub OPTION_MAP_UNIT_FN,
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complexity,
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"using `option.map(f)`, where `f` is a function or closure that returns `()`"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for usage of `result.map(f)` where f is a function
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/// or closure that returns the unit type `()`.
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///
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/// ### Why is this bad?
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/// Readability, this can be written more clearly with
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/// an if let statement
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///
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/// ### Example
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/// ```rust
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/// # fn do_stuff() -> Result<String, String> { Ok(String::new()) }
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/// # fn log_err_msg(foo: String) -> Result<String, String> { Ok(foo) }
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/// # fn format_msg(foo: String) -> String { String::new() }
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/// let x: Result<String, String> = do_stuff();
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/// x.map(log_err_msg);
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/// # let x: Result<String, String> = do_stuff();
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/// x.map(|msg| log_err_msg(format_msg(msg)));
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/// ```
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///
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/// The correct use would be:
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///
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/// ```rust
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/// # fn do_stuff() -> Result<String, String> { Ok(String::new()) }
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/// # fn log_err_msg(foo: String) -> Result<String, String> { Ok(foo) }
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/// # fn format_msg(foo: String) -> String { String::new() }
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/// let x: Result<String, String> = do_stuff();
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/// if let Ok(msg) = x {
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/// log_err_msg(msg);
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/// };
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/// # let x: Result<String, String> = do_stuff();
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/// if let Ok(msg) = x {
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/// log_err_msg(format_msg(msg));
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/// };
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub RESULT_MAP_UNIT_FN,
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complexity,
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"using `result.map(f)`, where `f` is a function or closure that returns `()`"
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}
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declare_lint_pass!(MapUnit => [OPTION_MAP_UNIT_FN, RESULT_MAP_UNIT_FN]);
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fn is_unit_type(ty: Ty<'_>) -> bool {
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ty.is_unit() || ty.is_never()
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}
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fn is_unit_function(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
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let ty = cx.typeck_results().expr_ty(expr);
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if let ty::FnDef(id, _) = *ty.kind() {
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if let Some(fn_type) = cx.tcx.fn_sig(id).subst_identity().no_bound_vars() {
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return is_unit_type(fn_type.output());
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}
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}
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false
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}
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fn is_unit_expression(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
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is_unit_type(cx.typeck_results().expr_ty(expr))
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}
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/// The expression inside a closure may or may not have surrounding braces and
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/// semicolons, which causes problems when generating a suggestion. Given an
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/// expression that evaluates to '()' or '!', recursively remove useless braces
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/// and semi-colons until is suitable for including in the suggestion template
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fn reduce_unit_expression(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<Span> {
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if !is_unit_expression(cx, expr) {
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return None;
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}
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match expr.kind {
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hir::ExprKind::Call(_, _) | hir::ExprKind::MethodCall(..) => {
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// Calls can't be reduced any more
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Some(expr.span)
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},
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hir::ExprKind::Block(block, _) => {
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match (block.stmts, block.expr.as_ref()) {
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([], Some(inner_expr)) => {
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// If block only contains an expression,
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// reduce `{ X }` to `X`
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reduce_unit_expression(cx, inner_expr)
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},
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([inner_stmt], None) => {
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// If block only contains statements,
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// reduce `{ X; }` to `X` or `X;`
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match inner_stmt.kind {
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hir::StmtKind::Local(local) => Some(local.span),
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hir::StmtKind::Expr(e) => Some(e.span),
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hir::StmtKind::Semi(..) => Some(inner_stmt.span),
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hir::StmtKind::Item(..) => None,
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}
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},
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_ => {
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// For closures that contain multiple statements
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// it's difficult to get a correct suggestion span
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// for all cases (multi-line closures specifically)
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//
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// We do not attempt to build a suggestion for those right now.
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None
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},
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}
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},
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_ => None,
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}
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}
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fn unit_closure<'tcx>(
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cx: &LateContext<'tcx>,
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expr: &hir::Expr<'_>,
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) -> Option<(&'tcx hir::Param<'tcx>, &'tcx hir::Expr<'tcx>)> {
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if_chain! {
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if let hir::ExprKind::Closure(&hir::Closure { fn_decl, body, .. }) = expr.kind;
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let body = cx.tcx.hir().body(body);
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let body_expr = &body.value;
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if fn_decl.inputs.len() == 1;
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if is_unit_expression(cx, body_expr);
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if let Some(binding) = iter_input_pats(fn_decl, body).next();
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then {
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return Some((binding, body_expr));
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}
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}
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None
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}
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/// Builds a name for the let binding variable (`var_arg`)
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///
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/// `x.field` => `x_field`
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/// `y` => `_y`
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///
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/// Anything else will return `a`.
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fn let_binding_name(cx: &LateContext<'_>, var_arg: &hir::Expr<'_>) -> String {
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match &var_arg.kind {
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hir::ExprKind::Field(_, _) => snippet(cx, var_arg.span, "_").replace('.', "_"),
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hir::ExprKind::Path(_) => format!("_{}", snippet(cx, var_arg.span, "")),
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_ => "a".to_string(),
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}
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}
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#[must_use]
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fn suggestion_msg(function_type: &str, map_type: &str) -> String {
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format!("called `map(f)` on an `{map_type}` value where `f` is a {function_type} that returns the unit type `()`")
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}
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fn lint_map_unit_fn(
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cx: &LateContext<'_>,
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stmt: &hir::Stmt<'_>,
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expr: &hir::Expr<'_>,
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map_args: (&hir::Expr<'_>, &[hir::Expr<'_>]),
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) {
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let var_arg = &map_args.0;
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let (map_type, variant, lint) = if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(var_arg), sym::Option) {
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("Option", "Some", OPTION_MAP_UNIT_FN)
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} else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(var_arg), sym::Result) {
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("Result", "Ok", RESULT_MAP_UNIT_FN)
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} else {
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return;
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};
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let fn_arg = &map_args.1[0];
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if is_unit_function(cx, fn_arg) {
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let mut applicability = Applicability::MachineApplicable;
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let msg = suggestion_msg("function", map_type);
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let suggestion = format!(
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"if let {0}({binding}) = {1} {{ {2}({binding}) }}",
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variant,
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snippet_with_applicability(cx, var_arg.span, "_", &mut applicability),
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snippet_with_applicability(cx, fn_arg.span, "_", &mut applicability),
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binding = let_binding_name(cx, var_arg)
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);
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span_lint_and_then(cx, lint, expr.span, &msg, |diag| {
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diag.span_suggestion(stmt.span, "try this", suggestion, applicability);
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});
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} else if let Some((binding, closure_expr)) = unit_closure(cx, fn_arg) {
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let msg = suggestion_msg("closure", map_type);
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span_lint_and_then(cx, lint, expr.span, &msg, |diag| {
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if let Some(reduced_expr_span) = reduce_unit_expression(cx, closure_expr) {
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let mut applicability = Applicability::MachineApplicable;
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let suggestion = format!(
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"if let {0}({1}) = {2} {{ {3} }}",
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variant,
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snippet_with_applicability(cx, binding.pat.span, "_", &mut applicability),
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snippet_with_applicability(cx, var_arg.span, "_", &mut applicability),
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snippet_with_context(cx, reduced_expr_span, var_arg.span.ctxt(), "_", &mut applicability).0,
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);
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diag.span_suggestion(stmt.span, "try this", suggestion, applicability);
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} else {
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let suggestion = format!(
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"if let {0}({1}) = {2} {{ ... }}",
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variant,
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snippet(cx, binding.pat.span, "_"),
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snippet(cx, var_arg.span, "_"),
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);
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diag.span_suggestion(stmt.span, "try this", suggestion, Applicability::HasPlaceholders);
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}
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});
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}
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}
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impl<'tcx> LateLintPass<'tcx> for MapUnit {
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fn check_stmt(&mut self, cx: &LateContext<'_>, stmt: &hir::Stmt<'_>) {
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if stmt.span.from_expansion() {
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return;
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}
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if let hir::StmtKind::Semi(expr) = stmt.kind {
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if let Some(arglists) = method_chain_args(expr, &["map"]) {
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lint_map_unit_fn(cx, stmt, expr, arglists[0]);
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}
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}
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}
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}
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