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

   1 use rustc::hir::*;
   2 use rustc::lint::*;
   3 use utils::{is_expn_of, match_def_path, resolve_node, span_lint};
   4 use utils::opt_def_id;
   5
   6 /// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
   7 /// replaced with `(e)print!()` / `(e)println!()`
   8 ///
   9 /// **Why is this bad?** Using `(e)println! is clearer and more concise
  10 ///
  11 /// **Known problems:** None.
  12 ///
  13 /// **Example:**
  14 /// ```rust
  15 /// // this would be clearer as `eprintln!("foo: {:?}", bar);`
  16 /// writeln!(&mut io::stderr(), "foo: {:?}", bar).unwrap();
  17 /// ```
  18 declare_lint! {
  19     pub EXPLICIT_WRITE,
  20     Warn,
  21     "using the `write!()` family of functions instead of the `print!()` family \
  22      of functions, when using the latter would work"
  23 }
  24
  25 #[derive(Copy, Clone, Debug)]
  26 pub struct Pass;
  27
  28 impl LintPass for Pass {
  29     fn get_lints(&self) -> LintArray {
  30         lint_array!(EXPLICIT_WRITE)
  31     }
  32 }
  33
  34 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  35     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  36         if_chain! {
  37             // match call to unwrap
  38             if let ExprMethodCall(ref unwrap_fun, _, ref unwrap_args) = expr.node;
  39             if unwrap_fun.name == "unwrap";
  40             // match call to write_fmt
  41             if unwrap_args.len() > 0;
  42             if let ExprMethodCall(ref write_fun, _, ref write_args) =
  43                 unwrap_args[0].node;
  44             if write_fun.name == "write_fmt";
  45             // match calls to std::io::stdout() / std::io::stderr ()
  46             if write_args.len() > 0;
  47             if let ExprCall(ref dest_fun, _) = write_args[0].node;
  48             if let ExprPath(ref qpath) = dest_fun.node;
  49             if let Some(dest_fun_id) =
  50                 opt_def_id(resolve_node(cx, qpath, dest_fun.hir_id));
  51             if let Some(dest_name) = if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stdout"]) {
  52                 Some("stdout")
  53             } else if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stderr"]) {
  54                 Some("stderr")
  55             } else {
  56                 None
  57             };
  58             then {
  59                 let write_span = unwrap_args[0].span;
  60                 let calling_macro =
  61                     // ordering is important here, since `writeln!` uses `write!` internally
  62                     if is_expn_of(write_span, "writeln").is_some() {
  63                         Some("writeln")
  64                     } else if is_expn_of(write_span, "write").is_some() {
  65                         Some("write")
  66                     } else {
  67                         None
  68                     };
  69                 let prefix = if dest_name == "stderr" {
  70                     "e"
  71                 } else {
  72                     ""
  73                 };
  74                 if let Some(macro_name) = calling_macro {
  75                     span_lint(
  76                         cx,
  77                         EXPLICIT_WRITE,
  78                         expr.span,
  79                         &format!(
  80                             "use of `{}!({}(), ...).unwrap()`. Consider using `{}{}!` instead",
  81                             macro_name,
  82                             dest_name,
  83                             prefix,
  84                             macro_name.replace("write", "print")
  85                         )
  86                     );
  87                 } else {
  88                     span_lint(
  89                         cx,
  90                         EXPLICIT_WRITE,
  91                         expr.span,
  92                         &format!(
  93                             "use of `{}().write_fmt(...).unwrap()`. Consider using `{}print!` instead",
  94                             dest_name,
  95                             prefix,
  96                         )
  97                     );
  98                 }
  99             }
 100         }
 101     }
 102 }