clippy_lints/src/explicit_write.rs

   1 use crate::rustc::hir::*;
   2 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use crate::rustc::{declare_tool_lint, lint_array};
   4 use if_chain::if_chain;
   5 use crate::utils::{is_expn_of, match_def_path, resolve_node, span_lint};
   6 use crate::utils::opt_def_id;
   7
   8 /// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
   9 /// replaced with `(e)print!()` / `(e)println!()`
  10 ///
  11 /// **Why is this bad?** Using `(e)println! is clearer and more concise
  12 ///
  13 /// **Known problems:** None.
  14 ///
  15 /// **Example:**
  16 /// ```rust
  17 /// // this would be clearer as `eprintln!("foo: {:?}", bar);`
  18 /// writeln!(&mut io::stderr(), "foo: {:?}", bar).unwrap();
  19 /// ```
  20 declare_clippy_lint! {
  21     pub EXPLICIT_WRITE,
  22     complexity,
  23     "using the `write!()` family of functions instead of the `print!()` family \
  24      of functions, when using the latter would work"
  25 }
  26
  27 #[derive(Copy, Clone, Debug)]
  28 pub struct Pass;
  29
  30 impl LintPass for Pass {
  31     fn get_lints(&self) -> LintArray {
  32         lint_array!(EXPLICIT_WRITE)
  33     }
  34 }
  35
  36 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  37     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  38         if_chain! {
  39             // match call to unwrap
  40             if let ExprKind::MethodCall(ref unwrap_fun, _, ref unwrap_args) = expr.node;
  41             if unwrap_fun.ident.name == "unwrap";
  42             // match call to write_fmt
  43             if unwrap_args.len() > 0;
  44             if let ExprKind::MethodCall(ref write_fun, _, ref write_args) =
  45                 unwrap_args[0].node;
  46             if write_fun.ident.name == "write_fmt";
  47             // match calls to std::io::stdout() / std::io::stderr ()
  48             if write_args.len() > 0;
  49             if let ExprKind::Call(ref dest_fun, _) = write_args[0].node;
  50             if let ExprKind::Path(ref qpath) = dest_fun.node;
  51             if let Some(dest_fun_id) =
  52                 opt_def_id(resolve_node(cx, qpath, dest_fun.hir_id));
  53             if let Some(dest_name) = if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stdout"]) {
  54                 Some("stdout")
  55             } else if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stderr"]) {
  56                 Some("stderr")
  57             } else {
  58                 None
  59             };
  60             then {
  61                 let write_span = unwrap_args[0].span;
  62                 let calling_macro =
  63                     // ordering is important here, since `writeln!` uses `write!` internally
  64                     if is_expn_of(write_span, "writeln").is_some() {
  65                         Some("writeln")
  66                     } else if is_expn_of(write_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                 if let Some(macro_name) = calling_macro {
  77                     span_lint(
  78                         cx,
  79                         EXPLICIT_WRITE,
  80                         expr.span,
  81                         &format!(
  82                             "use of `{}!({}(), ...).unwrap()`. Consider using `{}{}!` instead",
  83                             macro_name,
  84                             dest_name,
  85                             prefix,
  86                             macro_name.replace("write", "print")
  87                         )
  88                     );
  89                 } else {
  90                     span_lint(
  91                         cx,
  92                         EXPLICIT_WRITE,
  93                         expr.span,
  94                         &format!(
  95                             "use of `{}().write_fmt(...).unwrap()`. Consider using `{}print!` instead",
  96                             dest_name,
  97                             prefix,
  98                         )
  99                     );
 100                 }
 101             }
 102         }
 103     }
 104 }