1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::macros::FormatArgsExpn;
3 use clippy_utils::source::snippet_with_applicability;
4 use clippy_utils::{is_expn_of, match_function_call, paths};
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
7 use rustc_hir::def::Res;
8 use rustc_hir::{BindingAnnotation, Block, BlockCheckMode, Expr, ExprKind, Node, PatKind, QPath, Stmt, StmtKind};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 declare_clippy_lint! {
15 /// Checks for usage of `write!()` / `writeln()!` which can be
16 /// replaced with `(e)print!()` / `(e)println!()`
18 /// ### Why is this bad?
19 /// Using `(e)println! is clearer and more concise
23 /// # use std::io::Write;
24 /// # let bar = "furchtbar";
25 /// writeln!(&mut std::io::stderr(), "foo: {:?}", bar).unwrap();
26 /// writeln!(&mut std::io::stdout(), "foo: {:?}", bar).unwrap();
31 /// # use std::io::Write;
32 /// # let bar = "furchtbar";
33 /// eprintln!("foo: {:?}", bar);
34 /// println!("foo: {:?}", bar);
36 #[clippy::version = "pre 1.29.0"]
39 "using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
42 declare_lint_pass!(ExplicitWrite => [EXPLICIT_WRITE]);
44 impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
45 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
47 // match call to unwrap
48 if let ExprKind::MethodCall(unwrap_fun, write_call, [], _) = expr.kind;
49 if unwrap_fun.ident.name == sym::unwrap;
50 // match call to write_fmt
51 if let ExprKind::MethodCall(write_fun, write_recv, [write_arg], _) = look_in_block(cx, &write_call.kind);
52 if write_fun.ident.name == sym!(write_fmt);
53 // match calls to std::io::stdout() / std::io::stderr ()
54 if let Some(dest_name) = if match_function_call(cx, write_recv, &paths::STDOUT).is_some() {
56 } else if match_function_call(cx, write_recv, &paths::STDERR).is_some() {
61 if let Some(format_args) = FormatArgsExpn::parse(cx, write_arg);
64 // ordering is important here, since `writeln!` uses `write!` internally
65 if is_expn_of(write_call.span, "writeln").is_some() {
67 } else if is_expn_of(write_call.span, "write").is_some() {
72 let prefix = if dest_name == "stderr" {
78 // We need to remove the last trailing newline from the string because the
79 // underlying `fmt::write` function doesn't know whether `println!` or `print!` was
81 let (used, sugg_mac) = if let Some(macro_name) = calling_macro {
83 format!("{}!({}(), ...)", macro_name, dest_name),
84 macro_name.replace("write", "print"),
88 format!("{}().write_fmt(...)", dest_name),
92 let mut applicability = Applicability::MachineApplicable;
93 let inputs_snippet = snippet_with_applicability(
95 format_args.inputs_span(),
103 &format!("use of `{}.unwrap()`", used),
105 format!("{}{}!({})", prefix, sugg_mac, inputs_snippet),
113 /// If `kind` is a block that looks like `{ let result = $expr; result }` then
114 /// returns $expr. Otherwise returns `kind`.
115 fn look_in_block<'tcx, 'hir>(cx: &LateContext<'tcx>, kind: &'tcx ExprKind<'hir>) -> &'tcx ExprKind<'hir> {
117 if let ExprKind::Block(block, _label @ None) = kind;
119 stmts: [Stmt { kind: StmtKind::Local(local), .. }],
120 expr: Some(expr_end_of_block),
121 rules: BlockCheckMode::DefaultBlock,
125 // Find id of the local that expr_end_of_block resolves to
126 if let ExprKind::Path(QPath::Resolved(None, expr_path)) = expr_end_of_block.kind;
127 if let Res::Local(expr_res) = expr_path.res;
128 if let Some(Node::Pat(res_pat)) = cx.tcx.hir().find(expr_res);
130 // Find id of the local we found in the block
131 if let PatKind::Binding(BindingAnnotation::Unannotated, local_hir_id, _ident, None) = local.pat.kind;
133 // If those two are the same hir id
134 if res_pat.hir_id == local_hir_id;
136 if let Some(init) = local.init;