clippy_lints/src/explicit_write.rs

   1 use crate::utils::{is_expn_of, match_function_call, paths, span_lint, span_lint_and_sugg};
   2 use if_chain::if_chain;
   3 use rustc_ast::ast::LitKind;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{BorrowKind, Expr, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::sym;
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
  12     /// replaced with `(e)print!()` / `(e)println!()`
  13     ///
  14     /// **Why is this bad?** Using `(e)println! is clearer and more concise
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     /// ```rust
  20     /// # use std::io::Write;
  21     /// # let bar = "furchtbar";
  22     /// // this would be clearer as `eprintln!("foo: {:?}", bar);`
  23     /// writeln!(&mut std::io::stderr(), "foo: {:?}", bar).unwrap();
  24     /// ```
  25     pub EXPLICIT_WRITE,
  26     complexity,
  27     "using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
  28 }
  29
  30 declare_lint_pass!(ExplicitWrite => [EXPLICIT_WRITE]);
  31
  32 impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
  33     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  34         if_chain! {
  35             // match call to unwrap
  36             if let ExprKind::MethodCall(ref unwrap_fun, _, ref unwrap_args, _) = expr.kind;
  37             if unwrap_fun.ident.name == sym::unwrap;
  38             // match call to write_fmt
  39             if !unwrap_args.is_empty();
  40             if let ExprKind::MethodCall(ref write_fun, _, write_args, _) =
  41                 unwrap_args[0].kind;
  42             if write_fun.ident.name == sym!(write_fmt);
  43             // match calls to std::io::stdout() / std::io::stderr ()
  44             if !write_args.is_empty();
  45             if let Some(dest_name) = if match_function_call(cx, &write_args[0], &paths::STDOUT).is_some() {
  46                 Some("stdout")
  47             } else if match_function_call(cx, &write_args[0], &paths::STDERR).is_some() {
  48                 Some("stderr")
  49             } else {
  50                 None
  51             };
  52             then {
  53                 let write_span = unwrap_args[0].span;
  54                 let calling_macro =
  55                     // ordering is important here, since `writeln!` uses `write!` internally
  56                     if is_expn_of(write_span, "writeln").is_some() {
  57                         Some("writeln")
  58                     } else if is_expn_of(write_span, "write").is_some() {
  59                         Some("write")
  60                     } else {
  61                         None
  62                     };
  63                 let prefix = if dest_name == "stderr" {
  64                     "e"
  65                 } else {
  66                     ""
  67                 };
  68
  69                 // We need to remove the last trailing newline from the string because the
  70                 // underlying `fmt::write` function doesn't know whether `println!` or `print!` was
  71                 // used.
  72                 if let Some(mut write_output) = write_output_string(write_args) {
  73                     if write_output.ends_with('\n') {
  74                         write_output.pop();
  75                     }
  76
  77                     if let Some(macro_name) = calling_macro {
  78                         span_lint_and_sugg(
  79                             cx,
  80                             EXPLICIT_WRITE,
  81                             expr.span,
  82                             &format!(
  83                                 "use of `{}!({}(), ...).unwrap()`",
  84                                 macro_name,
  85                                 dest_name
  86                             ),
  87                             "try this",
  88                             format!("{}{}!(\"{}\")", prefix, macro_name.replace("write", "print"), write_output.escape_default()),
  89                             Applicability::MachineApplicable
  90                         );
  91                     } else {
  92                         span_lint_and_sugg(
  93                             cx,
  94                             EXPLICIT_WRITE,
  95                             expr.span,
  96                             &format!("use of `{}().write_fmt(...).unwrap()`", dest_name),
  97                             "try this",
  98                             format!("{}print!(\"{}\")", prefix, write_output.escape_default()),
  99                             Applicability::MachineApplicable
 100                         );
 101                     }
 102                 } else {
 103                     // We don't have a proper suggestion
 104                     if let Some(macro_name) = calling_macro {
 105                         span_lint(
 106                             cx,
 107                             EXPLICIT_WRITE,
 108                             expr.span,
 109                             &format!(
 110                                 "use of `{}!({}(), ...).unwrap()`. Consider using `{}{}!` instead",
 111                                 macro_name,
 112                                 dest_name,
 113                                 prefix,
 114                                 macro_name.replace("write", "print")
 115                             )
 116                         );
 117                     } else {
 118                         span_lint(
 119                             cx,
 120                             EXPLICIT_WRITE,
 121                             expr.span,
 122                             &format!("use of `{}().write_fmt(...).unwrap()`. Consider using `{}print!` instead", dest_name, prefix),
 123                         );
 124                     }
 125                 }
 126
 127             }
 128         }
 129     }
 130 }
 131
 132 // Extract the output string from the given `write_args`.
 133 fn write_output_string(write_args: &[Expr<'_>]) -> Option<String> {
 134     if_chain! {
 135         // Obtain the string that should be printed
 136         if write_args.len() > 1;
 137         if let ExprKind::Call(_, ref output_args) = write_args[1].kind;
 138         if !output_args.is_empty();
 139         if let ExprKind::AddrOf(BorrowKind::Ref, _, ref output_string_expr) = output_args[0].kind;
 140         if let ExprKind::Array(ref string_exprs) = output_string_expr.kind;
 141         // we only want to provide an automatic suggestion for simple (non-format) strings
 142         if string_exprs.len() == 1;
 143         if let ExprKind::Lit(ref lit) = string_exprs[0].kind;
 144         if let LitKind::Str(ref write_output, _) = lit.node;
 145         then {
 146             return Some(write_output.to_string())
 147         }
 148     }
 149     None
 150 }