clippy_lints/src/explicit_write.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::rustc::hir::*;
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use crate::syntax::ast::LitKind;
  14 use crate::utils::{is_expn_of, match_def_path, opt_def_id, resolve_node, span_lint, span_lint_and_sugg};
  15 use if_chain::if_chain;
  16
  17 /// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
  18 /// replaced with `(e)print!()` / `(e)println!()`
  19 ///
  20 /// **Why is this bad?** Using `(e)println! is clearer and more concise
  21 ///
  22 /// **Known problems:** None.
  23 ///
  24 /// **Example:**
  25 /// ```rust
  26 /// // this would be clearer as `eprintln!("foo: {:?}", bar);`
  27 /// writeln!(&mut io::stderr(), "foo: {:?}", bar).unwrap();
  28 /// ```
  29 declare_clippy_lint! {
  30     pub EXPLICIT_WRITE,
  31     complexity,
  32     "using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
  33 }
  34
  35 #[derive(Copy, Clone, Debug)]
  36 pub struct Pass;
  37
  38 impl LintPass for Pass {
  39     fn get_lints(&self) -> LintArray {
  40         lint_array!(EXPLICIT_WRITE)
  41     }
  42 }
  43
  44 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  45     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  46         if_chain! {
  47             // match call to unwrap
  48             if let ExprKind::MethodCall(ref unwrap_fun, _, ref unwrap_args) = expr.node;
  49             if unwrap_fun.ident.name == "unwrap";
  50             // match call to write_fmt
  51             if unwrap_args.len() > 0;
  52             if let ExprKind::MethodCall(ref write_fun, _, ref write_args) =
  53                 unwrap_args[0].node;
  54             if write_fun.ident.name == "write_fmt";
  55             // match calls to std::io::stdout() / std::io::stderr ()
  56             if write_args.len() > 0;
  57             if let ExprKind::Call(ref dest_fun, _) = write_args[0].node;
  58             if let ExprKind::Path(ref qpath) = dest_fun.node;
  59             if let Some(dest_fun_id) =
  60                 opt_def_id(resolve_node(cx, qpath, dest_fun.hir_id));
  61             if let Some(dest_name) = if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stdout"]) {
  62                 Some("stdout")
  63             } else if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stderr"]) {
  64                 Some("stderr")
  65             } else {
  66                 None
  67             };
  68             then {
  69                 let write_span = unwrap_args[0].span;
  70                 let calling_macro =
  71                     // ordering is important here, since `writeln!` uses `write!` internally
  72                     if is_expn_of(write_span, "writeln").is_some() {
  73                         Some("writeln")
  74                     } else if is_expn_of(write_span, "write").is_some() {
  75                         Some("write")
  76                     } else {
  77                         None
  78                     };
  79                 let prefix = if dest_name == "stderr" {
  80                     "e"
  81                 } else {
  82                     ""
  83                 };
  84
  85                 // We need to remove the last trailing newline from the string because the
  86                 // underlying `fmt::write` function doesn't know wether `println!` or `print!` was
  87                 // used.
  88                 let mut write_output: String = write_output_string(write_args).unwrap();
  89                 if write_output.ends_with('\n') {
  90                     write_output.truncate(write_output.len() - 1)
  91                 }
  92                 if let Some(macro_name) = calling_macro {
  93                     span_lint_and_sugg(
  94                         cx,
  95                         EXPLICIT_WRITE,
  96                         expr.span,
  97                         &format!(
  98                             "use of `{}!({}(), ...).unwrap()`",
  99                             macro_name,
 100                             dest_name
 101                         ),
 102                         "try this",
 103                         format!("{}{}!(\"{}\")", prefix, macro_name.replace("write", "print"), write_output.escape_default())
 104                     );
 105                 } else {
 106                     span_lint_and_sugg(
 107                         cx,
 108                         EXPLICIT_WRITE,
 109                         expr.span,
 110                         &format!("use of `{}().write_fmt(...).unwrap()`", dest_name),
 111                         "try this",
 112                         format!("{}print!(\"{}\")", prefix, write_output.escape_default())
 113                     );
 114                 }
 115             }
 116         }
 117     }
 118 }
 119
 120 // Extract the output string from the given `write_args`.
 121 fn write_output_string(write_args: &HirVec<Expr>) -> Option<String> {
 122     if_chain! {
 123         // Obtain the string that should be printed
 124         if write_args.len() > 1;
 125         if let ExprKind::Call(_, ref output_args) = write_args[1].node;
 126         if output_args.len() > 0;
 127         if let ExprKind::AddrOf(_, ref output_string_expr) = output_args[0].node;
 128         if let ExprKind::Array(ref string_exprs) = output_string_expr.node;
 129         if string_exprs.len() > 0;
 130         if let ExprKind::Lit(ref lit) = string_exprs[0].node;
 131         if let LitKind::Str(ref write_output, _) = lit.node;
 132         then {
 133             return Some(write_output.to_string())
 134         }
 135     }
 136     None
 137 }