+ cx.tcx.def_path_str(def_id),
+ Applicability::MachineApplicable,
+ );
+ }
+ }
+ if let ExprKind::Binary(op, left, right) = expr.kind {
+ if matches!(op.node, BinOpKind::Eq | BinOpKind::Ne) {
+ let data = [
+ (left, self.symbol_str_expr(left, cx)),
+ (right, self.symbol_str_expr(right, cx)),
+ ];
+ match data {
+ // both operands are a symbol string
+ [(_, Some(left)), (_, Some(right))] => {
+ span_lint_and_sugg(
+ cx,
+ UNNECESSARY_SYMBOL_STR,
+ expr.span,
+ "unnecessary `Symbol` to string conversion",
+ "try",
+ format!(
+ "{} {} {}",
+ left.as_symbol_snippet(cx),
+ op.node.as_str(),
+ right.as_symbol_snippet(cx),
+ ),
+ Applicability::MachineApplicable,
+ );
+ },
+ // one of the operands is a symbol string
+ [(expr, Some(symbol)), _] | [_, (expr, Some(symbol))] => {
+ // creating an owned string for comparison
+ if matches!(symbol, SymbolStrExpr::Expr { is_to_owned: true, .. }) {
+ span_lint_and_sugg(
+ cx,
+ UNNECESSARY_SYMBOL_STR,
+ expr.span,
+ "unnecessary string allocation",
+ "try",
+ format!("{}.as_str()", symbol.as_symbol_snippet(cx)),
+ Applicability::MachineApplicable,
+ );
+ }
+ },
+ // nothing found
+ [(_, None), (_, None)] => {},
+ }
+ }
+ }
+ }
+}
+
+impl InterningDefinedSymbol {
+ fn symbol_str_expr<'tcx>(&self, expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> Option<SymbolStrExpr<'tcx>> {
+ static IDENT_STR_PATHS: &[&[&str]] = &[&paths::IDENT_AS_STR, &paths::TO_STRING_METHOD];
+ static SYMBOL_STR_PATHS: &[&[&str]] = &[
+ &paths::SYMBOL_AS_STR,
+ &paths::SYMBOL_TO_IDENT_STRING,
+ &paths::TO_STRING_METHOD,
+ ];
+ let call = if_chain! {
+ if let ExprKind::AddrOf(_, _, e) = expr.kind;
+ if let ExprKind::Unary(UnOp::Deref, e) = e.kind;
+ then { e } else { expr }
+ };
+ if_chain! {
+ // is a method call
+ if let ExprKind::MethodCall(_, [item], _) = call.kind;
+ if let Some(did) = cx.typeck_results().type_dependent_def_id(call.hir_id);
+ let ty = cx.typeck_results().expr_ty(item);
+ // ...on either an Ident or a Symbol
+ if let Some(is_ident) = if match_type(cx, ty, &paths::SYMBOL) {
+ Some(false)
+ } else if match_type(cx, ty, &paths::IDENT) {
+ Some(true)
+ } else {
+ None
+ };
+ // ...which converts it to a string
+ let paths = if is_ident { IDENT_STR_PATHS } else { SYMBOL_STR_PATHS };
+ if let Some(path) = paths.iter().find(|path| match_def_path(cx, did, path));
+ then {
+ let is_to_owned = path.last().unwrap().ends_with("string");
+ return Some(SymbolStrExpr::Expr {
+ item,
+ is_ident,
+ is_to_owned,
+ });
+ }
+ }
+ // is a string constant
+ if let Some(Constant::Str(s)) = constant_simple(cx, cx.typeck_results(), expr) {
+ let value = Symbol::intern(&s).as_u32();
+ // ...which matches a symbol constant
+ if let Some(&def_id) = self.symbol_map.get(&value) {
+ return Some(SymbolStrExpr::Const(def_id));
+ }
+ }
+ None
+ }
+}
+
+enum SymbolStrExpr<'tcx> {
+ /// a string constant with a corresponding symbol constant
+ Const(DefId),
+ /// a "symbol to string" expression like `symbol.as_str()`
+ Expr {
+ /// part that evaluates to `Symbol` or `Ident`
+ item: &'tcx Expr<'tcx>,
+ is_ident: bool,
+ /// whether an owned `String` is created like `to_ident_string()`
+ is_to_owned: bool,
+ },
+}
+
+impl<'tcx> SymbolStrExpr<'tcx> {
+ /// Returns a snippet that evaluates to a `Symbol` and is const if possible
+ fn as_symbol_snippet(&self, cx: &LateContext<'_>) -> Cow<'tcx, str> {
+ match *self {
+ Self::Const(def_id) => cx.tcx.def_path_str(def_id).into(),
+ Self::Expr { item, is_ident, .. } => {
+ let mut snip = snippet(cx, item.span.source_callsite(), "..");
+ if is_ident {
+ // get `Ident.name`
+ snip.to_mut().push_str(".name");
+ }
+ snip
+ },
+ }
+ }
+}
+
+declare_lint_pass!(IfChainStyle => [IF_CHAIN_STYLE]);
+
+impl<'tcx> LateLintPass<'tcx> for IfChainStyle {
+ fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
+ let (local, after, if_chain_span) = if_chain! {
+ if let [Stmt { kind: StmtKind::Local(local), .. }, after @ ..] = block.stmts;
+ if let Some(if_chain_span) = is_expn_of(block.span, "if_chain");
+ then { (local, after, if_chain_span) } else { return }
+ };
+ if is_first_if_chain_expr(cx, block.hir_id, if_chain_span) {
+ span_lint(
+ cx,
+ IF_CHAIN_STYLE,
+ if_chain_local_span(cx, local, if_chain_span),
+ "`let` expression should be above the `if_chain!`",
+ );
+ } else if local.span.ctxt() == block.span.ctxt() && is_if_chain_then(after, block.expr, if_chain_span) {
+ span_lint(
+ cx,
+ IF_CHAIN_STYLE,
+ if_chain_local_span(cx, local, if_chain_span),
+ "`let` expression should be inside `then { .. }`",
+ );
+ }
+ }
+
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+ let (cond, then, els) = if let Some(higher::IfOrIfLet { cond, r#else, then }) = higher::IfOrIfLet::hir(expr) {
+ (cond, then, r#else.is_some())
+ } else {
+ return;
+ };
+ let then_block = match then.kind {
+ ExprKind::Block(block, _) => block,
+ _ => return,
+ };
+ let if_chain_span = is_expn_of(expr.span, "if_chain");
+ if !els {
+ check_nested_if_chains(cx, expr, then_block, if_chain_span);
+ }
+ let if_chain_span = match if_chain_span {
+ None => return,
+ Some(span) => span,
+ };
+ // check for `if a && b;`
+ if_chain! {
+ if let ExprKind::Binary(op, _, _) = cond.kind;
+ if op.node == BinOpKind::And;
+ if cx.sess().source_map().is_multiline(cond.span);
+ then {
+ span_lint(cx, IF_CHAIN_STYLE, cond.span, "`if a && b;` should be `if a; if b;`");
+ }
+ }
+ if is_first_if_chain_expr(cx, expr.hir_id, if_chain_span)
+ && is_if_chain_then(then_block.stmts, then_block.expr, if_chain_span)
+ {
+ span_lint(cx, IF_CHAIN_STYLE, expr.span, "`if_chain!` only has one `if`");
+ }
+ }
+}
+
+fn check_nested_if_chains(
+ cx: &LateContext<'_>,
+ if_expr: &Expr<'_>,
+ then_block: &Block<'_>,
+ if_chain_span: Option<Span>,
+) {
+ #[rustfmt::skip]
+ let (head, tail) = match *then_block {
+ Block { stmts, expr: Some(tail), .. } => (stmts, tail),
+ Block {
+ stmts: &[
+ ref head @ ..,
+ Stmt { kind: StmtKind::Expr(tail) | StmtKind::Semi(tail), .. }
+ ],
+ ..
+ } => (head, tail),
+ _ => return,
+ };
+ if_chain! {
+ if let Some(higher::IfOrIfLet { r#else: None, .. }) = higher::IfOrIfLet::hir(tail);
+ let sm = cx.sess().source_map();
+ if head
+ .iter()
+ .all(|stmt| matches!(stmt.kind, StmtKind::Local(..)) && !sm.is_multiline(stmt.span));
+ if if_chain_span.is_some() || !is_else_clause(cx.tcx, if_expr);
+ then {} else { return }
+ }
+ let (span, msg) = match (if_chain_span, is_expn_of(tail.span, "if_chain")) {
+ (None, Some(_)) => (if_expr.span, "this `if` can be part of the inner `if_chain!`"),
+ (Some(_), None) => (tail.span, "this `if` can be part of the outer `if_chain!`"),
+ (Some(a), Some(b)) if a != b => (b, "this `if_chain!` can be merged with the outer `if_chain!`"),
+ _ => return,
+ };
+ span_lint_and_then(cx, IF_CHAIN_STYLE, span, msg, |diag| {
+ let (span, msg) = match head {
+ [] => return,
+ [stmt] => (stmt.span, "this `let` statement can also be in the `if_chain!`"),
+ [a, .., b] => (
+ a.span.to(b.span),
+ "these `let` statements can also be in the `if_chain!`",
+ ),
+ };
+ diag.span_help(span, msg);
+ });
+}
+
+fn is_first_if_chain_expr(cx: &LateContext<'_>, hir_id: HirId, if_chain_span: Span) -> bool {
+ cx.tcx
+ .hir()
+ .parent_iter(hir_id)
+ .find(|(_, node)| {
+ #[rustfmt::skip]
+ !matches!(node, Node::Expr(Expr { kind: ExprKind::Block(..), .. }) | Node::Stmt(_))
+ })
+ .map_or(false, |(id, _)| {
+ is_expn_of(cx.tcx.hir().span(id), "if_chain") != Some(if_chain_span)
+ })
+}
+
+/// Checks a trailing slice of statements and expression of a `Block` to see if they are part
+/// of the `then {..}` portion of an `if_chain!`
+fn is_if_chain_then(stmts: &[Stmt<'_>], expr: Option<&Expr<'_>>, if_chain_span: Span) -> bool {
+ let span = if let [stmt, ..] = stmts {
+ stmt.span
+ } else if let Some(expr) = expr {
+ expr.span
+ } else {
+ // empty `then {}`
+ return true;
+ };
+ is_expn_of(span, "if_chain").map_or(true, |span| span != if_chain_span)
+}
+
+/// Creates a `Span` for `let x = ..;` in an `if_chain!` call.
+fn if_chain_local_span(cx: &LateContext<'_>, local: &Local<'_>, if_chain_span: Span) -> Span {
+ let mut span = local.pat.span;
+ if let Some(init) = local.init {
+ span = span.to(init.span);
+ }
+ span.adjust(if_chain_span.ctxt().outer_expn());
+ let sm = cx.sess().source_map();
+ let span = sm.span_extend_to_prev_str(span, "let", false, true).unwrap_or(span);
+ let span = sm.span_extend_to_next_char(span, ';', false);
+ Span::new(
+ span.lo() - BytePos(3),
+ span.hi() + BytePos(1),
+ span.ctxt(),
+ span.parent(),
+ )
+}
+
+declare_lint_pass!(MsrvAttrImpl => [MISSING_MSRV_ATTR_IMPL]);
+
+impl LateLintPass<'_> for MsrvAttrImpl {
+ fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
+ if_chain! {
+ if let hir::ItemKind::Impl(hir::Impl {
+ of_trait: Some(lint_pass_trait_ref),
+ self_ty,
+ items,
+ ..
+ }) = &item.kind;
+ if let Some(lint_pass_trait_def_id) = lint_pass_trait_ref.trait_def_id();
+ let is_late_pass = match_def_path(cx, lint_pass_trait_def_id, &paths::LATE_LINT_PASS);
+ if is_late_pass || match_def_path(cx, lint_pass_trait_def_id, &paths::EARLY_LINT_PASS);
+ let self_ty = hir_ty_to_ty(cx.tcx, self_ty);
+ if let ty::Adt(self_ty_def, _) = self_ty.kind();
+ if self_ty_def.is_struct();
+ if self_ty_def.all_fields().any(|f| {
+ cx.tcx
+ .type_of(f.did)
+ .walk()
+ .filter(|t| matches!(t.unpack(), GenericArgKind::Type(_)))
+ .any(|t| match_type(cx, t.expect_ty(), &paths::RUSTC_VERSION))
+ });
+ if !items.iter().any(|item| item.ident.name == sym!(enter_lint_attrs));
+ then {
+ let context = if is_late_pass { "LateContext" } else { "EarlyContext" };
+ let lint_pass = if is_late_pass { "LateLintPass" } else { "EarlyLintPass" };
+ let span = cx.sess().source_map().span_through_char(item.span, '{');
+ span_lint_and_sugg(
+ cx,
+ MISSING_MSRV_ATTR_IMPL,
+ span,
+ &format!("`extract_msrv_attr!` macro missing from `{lint_pass}` implementation"),
+ &format!("add `extract_msrv_attr!({context})` to the `{lint_pass}` implementation"),
+ format!("{}\n extract_msrv_attr!({context});", snippet(cx, span, "..")),