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_let_chain! {[
  37             // match call to unwrap
  38             let ExprMethodCall(ref unwrap_fun, _, ref unwrap_args) = expr.node,
  39             unwrap_fun.name == "unwrap",
  40             // match call to write_fmt
  41             unwrap_args.len() > 0,
  42             let ExprMethodCall(ref write_fun, _, ref write_args) =
  43                 unwrap_args[0].node,
  44             write_fun.name == "write_fmt",
  45             // match calls to std::io::stdout() / std::io::stderr ()
  46             write_args.len() > 0,
  47             let ExprCall(ref dest_fun, _) = write_args[0].node,
  48             let ExprPath(ref qpath) = dest_fun.node,
  49             let Some(dest_fun_id) =
  50                 opt_def_id(resolve_node(cx, qpath, dest_fun.hir_id)),
  51             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         ], {
  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 }