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::utils::{is_expn_of, match_def_path, opt_def_id, resolve_node, span_lint, span_lint_and_sugg};
  11 use if_chain::if_chain;
  12 use rustc::hir::*;
  13 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  14 use rustc::{declare_tool_lint, lint_array};
  15 use rustc_errors::Applicability;
  16 use syntax::ast::LitKind;
  17
  18 /// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
  19 /// replaced with `(e)print!()` / `(e)println!()`
  20 ///
  21 /// **Why is this bad?** Using `(e)println! is clearer and more concise
  22 ///
  23 /// **Known problems:** None.
  24 ///
  25 /// **Example:**
  26 /// ```rust
  27 /// // this would be clearer as `eprintln!("foo: {:?}", bar);`
  28 /// writeln!(&mut io::stderr(), "foo: {:?}", bar).unwrap();
  29 /// ```
  30 declare_clippy_lint! {
  31     pub EXPLICIT_WRITE,
  32     complexity,
  33     "using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
  34 }
  35
  36 #[derive(Copy, Clone, Debug)]
  37 pub struct Pass;
  38
  39 impl LintPass for Pass {
  40     fn get_lints(&self) -> LintArray {
  41         lint_array!(EXPLICIT_WRITE)
  42     }
  43 }
  44
  45 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  46     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  47         if_chain! {
  48             // match call to unwrap
  49             if let ExprKind::MethodCall(ref unwrap_fun, _, ref unwrap_args) = expr.node;
  50             if unwrap_fun.ident.name == "unwrap";
  51             // match call to write_fmt
  52             if unwrap_args.len() > 0;
  53             if let ExprKind::MethodCall(ref write_fun, _, ref write_args) =
  54                 unwrap_args[0].node;
  55             if write_fun.ident.name == "write_fmt";
  56             // match calls to std::io::stdout() / std::io::stderr ()
  57             if write_args.len() > 0;
  58             if let ExprKind::Call(ref dest_fun, _) = write_args[0].node;
  59             if let ExprKind::Path(ref qpath) = dest_fun.node;
  60             if let Some(dest_fun_id) =
  61                 opt_def_id(resolve_node(cx, qpath, dest_fun.hir_id));
  62             if let Some(dest_name) = if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stdout"]) {
  63                 Some("stdout")
  64             } else if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stderr"]) {
  65                 Some("stderr")
  66             } else {
  67                 None
  68             };
  69             then {
  70                 let write_span = unwrap_args[0].span;
  71                 let calling_macro =
  72                     // ordering is important here, since `writeln!` uses `write!` internally
  73                     if is_expn_of(write_span, "writeln").is_some() {
  74                         Some("writeln")
  75                     } else if is_expn_of(write_span, "write").is_some() {
  76                         Some("write")
  77                     } else {
  78                         None
  79                     };
  80                 let prefix = if dest_name == "stderr" {
  81                     "e"
  82                 } else {
  83                     ""
  84                 };
  85
  86                 // We need to remove the last trailing newline from the string because the
  87                 // underlying `fmt::write` function doesn't know whether `println!` or `print!` was
  88                 // used.
  89                 if let Some(mut write_output) = write_output_string(write_args) {
  90                     if write_output.ends_with('\n') {
  91                         write_output.pop();
  92                     }
  93
  94                     if let Some(macro_name) = calling_macro {
  95                         span_lint_and_sugg(
  96                             cx,
  97                             EXPLICIT_WRITE,
  98                             expr.span,
  99                             &format!(
 100                                 "use of `{}!({}(), ...).unwrap()`",
 101                                 macro_name,
 102                                 dest_name
 103                             ),
 104                             "try this",
 105                             format!("{}{}!(\"{}\")", prefix, macro_name.replace("write", "print"), write_output.escape_default()),
 106                             Applicability::MachineApplicable
 107                         );
 108                     } else {
 109                         span_lint_and_sugg(
 110                             cx,
 111                             EXPLICIT_WRITE,
 112                             expr.span,
 113                             &format!("use of `{}().write_fmt(...).unwrap()`", dest_name),
 114                             "try this",
 115                             format!("{}print!(\"{}\")", prefix, write_output.escape_default()),
 116                             Applicability::MachineApplicable
 117                         );
 118                     }
 119                 } else {
 120                     // We don't have a proper suggestion
 121                     if let Some(macro_name) = calling_macro {
 122                         span_lint(
 123                             cx,
 124                             EXPLICIT_WRITE,
 125                             expr.span,
 126                             &format!(
 127                                 "use of `{}!({}(), ...).unwrap()`. Consider using `{}{}!` instead",
 128                                 macro_name,
 129                                 dest_name,
 130                                 prefix,
 131                                 macro_name.replace("write", "print")
 132                             )
 133                         );
 134                     } else {
 135                         span_lint(
 136                             cx,
 137                             EXPLICIT_WRITE,
 138                             expr.span,
 139                             &format!("use of `{}().write_fmt(...).unwrap()`. Consider using `{}print!` instead", dest_name, prefix),
 140                         );
 141                     }
 142                 }
 143
 144             }
 145         }
 146     }
 147 }
 148
 149 // Extract the output string from the given `write_args`.
 150 fn write_output_string(write_args: &HirVec<Expr>) -> Option<String> {
 151     if_chain! {
 152         // Obtain the string that should be printed
 153         if write_args.len() > 1;
 154         if let ExprKind::Call(_, ref output_args) = write_args[1].node;
 155         if output_args.len() > 0;
 156         if let ExprKind::AddrOf(_, ref output_string_expr) = output_args[0].node;
 157         if let ExprKind::Array(ref string_exprs) = output_string_expr.node;
 158         if string_exprs.len() > 0;
 159         if let ExprKind::Lit(ref lit) = string_exprs[0].node;
 160         if let LitKind::Str(ref write_output, _) = lit.node;
 161         then {
 162             return Some(write_output.to_string())
 163         }
 164     }
 165     None
 166 }