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

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