1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::macros::{find_format_args, format_args_inputs_span};
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};
11 use rustc_span::{sym, ExpnId};
12
13 declare_clippy_lint! {
14 /// ### What it does
15 /// Checks for usage of `write!()` / `writeln()!` which can be
16 /// replaced with `(e)print!()` / `(e)println!()`
17 ///
18 /// ### Why is this bad?
19 /// Using `(e)println! is clearer and more concise
20 ///
21 /// ### Example
22 /// ```rust
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();
27 /// ```
28 ///
29 /// Use instead:
30 /// ```rust
31 /// # use std::io::Write;
32 /// # let bar = "furchtbar";
33 /// eprintln!("foo: {:?}", bar);
34 /// println!("foo: {:?}", bar);
35 /// ```
36 #[clippy::version = "pre 1.29.0"]
37 pub EXPLICIT_WRITE,
38 complexity,
39 "using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
40 }
41
42 declare_lint_pass!(ExplicitWrite => [EXPLICIT_WRITE]);
43
44 impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>)45 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
46 // match call to unwrap
47 if let ExprKind::MethodCall(unwrap_fun, write_call, [], _) = expr.kind
48 && unwrap_fun.ident.name == sym::unwrap
49 // match call to write_fmt
50 && let ExprKind::MethodCall(write_fun, write_recv, [write_arg], _) = look_in_block(cx, &write_call.kind)
51 && write_fun.ident.name == sym!(write_fmt)
52 // match calls to std::io::stdout() / std::io::stderr ()
53 && let Some(dest_name) = if match_function_call(cx, write_recv, &paths::STDOUT).is_some() {
54 Some("stdout")
55 } else if match_function_call(cx, write_recv, &paths::STDERR).is_some() {
56 Some("stderr")
57 } else {
58 None
59 }
60 {
61 find_format_args(cx, write_arg, ExpnId::root(), |format_args| {
62 let calling_macro =
63 // ordering is important here, since `writeln!` uses `write!` internally
64 if is_expn_of(write_call.span, "writeln").is_some() {
65 Some("writeln")
66 } else if is_expn_of(write_call.span, "write").is_some() {
67 Some("write")
68 } else {
69 None
70 };
71 let prefix = if dest_name == "stderr" {
72 "e"
73 } else {
74 ""
75 };
76
77 // We need to remove the last trailing newline from the string because the
78 // underlying `fmt::write` function doesn't know whether `println!` or `print!` was
79 // used.
80 let (used, sugg_mac) = if let Some(macro_name) = calling_macro {
81 (
82 format!("{macro_name}!({dest_name}(), ...)"),
83 macro_name.replace("write", "print"),
84 )
85 } else {
86 (
87 format!("{dest_name}().write_fmt(...)"),
88 "print".into(),
89 )
90 };
91 let mut applicability = Applicability::MachineApplicable;
92 let inputs_snippet = snippet_with_applicability(
93 cx,
94 format_args_inputs_span(format_args),
95 "..",
96 &mut applicability,
97 );
98 span_lint_and_sugg(
99 cx,
100 EXPLICIT_WRITE,
101 expr.span,
102 &format!("use of `{used}.unwrap()`"),
103 "try this",
104 format!("{prefix}{sugg_mac}!({inputs_snippet})"),
105 applicability,
106 );
107 });
108 }
109 }
110 }
111
112 /// If `kind` is a block that looks like `{ let result = $expr; result }` then
113 /// returns $expr. Otherwise returns `kind`.
look_in_block<'tcx, 'hir>(cx: &LateContext<'tcx>, kind: &'tcx ExprKind<'hir>) -> &'tcx ExprKind<'hir>114 fn look_in_block<'tcx, 'hir>(cx: &LateContext<'tcx>, kind: &'tcx ExprKind<'hir>) -> &'tcx ExprKind<'hir> {
115 if_chain! {
116 if let ExprKind::Block(block, _label @ None) = kind;
117 if let Block {
118 stmts: [Stmt { kind: StmtKind::Local(local), .. }],
119 expr: Some(expr_end_of_block),
120 rules: BlockCheckMode::DefaultBlock,
121 ..
122 } = block;
123
124 // Find id of the local that expr_end_of_block resolves to
125 if let ExprKind::Path(QPath::Resolved(None, expr_path)) = expr_end_of_block.kind;
126 if let Res::Local(expr_res) = expr_path.res;
127 if let Some(Node::Pat(res_pat)) = cx.tcx.hir().find(expr_res);
128
129 // Find id of the local we found in the block
130 if let PatKind::Binding(BindingAnnotation::NONE, local_hir_id, _ident, None) = local.pat.kind;
131
132 // If those two are the same hir id
133 if res_pat.hir_id == local_hir_id;
134
135 if let Some(init) = local.init;
136 then {
137 return &init.kind;
138 }
139 }
140 kind
141 }
142