src/tools/clippy/clippy_lints/src/explicit_write.rs

   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 {
  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`.
 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 }