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

   1 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
   2 use clippy_utils::{is_expn_of, match_function_call, paths};
   3 use if_chain::if_chain;
   4 use rustc_ast::ast::LitKind;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{BorrowKind, Expr, ExprKind};
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9 use rustc_span::sym;
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
  13     /// replaced with `(e)print!()` / `(e)println!()`
  14     ///
  15     /// **Why is this bad?** Using `(e)println! is clearer and more concise
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     /// ```rust
  21     /// # use std::io::Write;
  22     /// # let bar = "furchtbar";
  23     /// // this would be clearer as `eprintln!("foo: {:?}", bar);`
  24     /// writeln!(&mut std::io::stderr(), "foo: {:?}", bar).unwrap();
  25     /// ```
  26     pub EXPLICIT_WRITE,
  27     complexity,
  28     "using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
  29 }
  30
  31 declare_lint_pass!(ExplicitWrite => [EXPLICIT_WRITE]);
  32
  33 impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
  34     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  35         if_chain! {
  36             // match call to unwrap
  37             if let ExprKind::MethodCall(unwrap_fun, _, unwrap_args, _) = expr.kind;
  38             if unwrap_fun.ident.name == sym::unwrap;
  39             // match call to write_fmt
  40             if !unwrap_args.is_empty();
  41             if let ExprKind::MethodCall(write_fun, _, write_args, _) =
  42                 unwrap_args[0].kind;
  43             if write_fun.ident.name == sym!(write_fmt);
  44             // match calls to std::io::stdout() / std::io::stderr ()
  45             if !write_args.is_empty();
  46             if let Some(dest_name) = if match_function_call(cx, &write_args[0], &paths::STDOUT).is_some() {
  47                 Some("stdout")
  48             } else if match_function_call(cx, &write_args[0], &paths::STDERR).is_some() {
  49                 Some("stderr")
  50             } else {
  51                 None
  52             };
  53             then {
  54                 let write_span = unwrap_args[0].span;
  55                 let calling_macro =
  56                     // ordering is important here, since `writeln!` uses `write!` internally
  57                     if is_expn_of(write_span, "writeln").is_some() {
  58                         Some("writeln")
  59                     } else if is_expn_of(write_span, "write").is_some() {
  60                         Some("write")
  61                     } else {
  62                         None
  63                     };
  64                 let prefix = if dest_name == "stderr" {
  65                     "e"
  66                 } else {
  67                     ""
  68                 };
  69
  70                 // We need to remove the last trailing newline from the string because the
  71                 // underlying `fmt::write` function doesn't know whether `println!` or `print!` was
  72                 // used.
  73                 if let Some(mut write_output) = write_output_string(write_args) {
  74                     if write_output.ends_with('\n') {
  75                         write_output.pop();
  76                     }
  77
  78                     if let Some(macro_name) = calling_macro {
  79                         span_lint_and_sugg(
  80                             cx,
  81                             EXPLICIT_WRITE,
  82                             expr.span,
  83                             &format!(
  84                                 "use of `{}!({}(), ...).unwrap()`",
  85                                 macro_name,
  86                                 dest_name
  87                             ),
  88                             "try this",
  89                             format!("{}{}!(\"{}\")", prefix, macro_name.replace("write", "print"), write_output.escape_default()),
  90                             Applicability::MachineApplicable
  91                         );
  92                     } else {
  93                         span_lint_and_sugg(
  94                             cx,
  95                             EXPLICIT_WRITE,
  96                             expr.span,
  97                             &format!("use of `{}().write_fmt(...).unwrap()`", dest_name),
  98                             "try this",
  99                             format!("{}print!(\"{}\")", prefix, write_output.escape_default()),
 100                             Applicability::MachineApplicable
 101                         );
 102                     }
 103                 } else {
 104                     // We don't have a proper suggestion
 105                     if let Some(macro_name) = calling_macro {
 106                         span_lint(
 107                             cx,
 108                             EXPLICIT_WRITE,
 109                             expr.span,
 110                             &format!(
 111                                 "use of `{}!({}(), ...).unwrap()`. Consider using `{}{}!` instead",
 112                                 macro_name,
 113                                 dest_name,
 114                                 prefix,
 115                                 macro_name.replace("write", "print")
 116                             )
 117                         );
 118                     } else {
 119                         span_lint(
 120                             cx,
 121                             EXPLICIT_WRITE,
 122                             expr.span,
 123                             &format!("use of `{}().write_fmt(...).unwrap()`. Consider using `{}print!` instead", dest_name, prefix),
 124                         );
 125                     }
 126                 }
 127
 128             }
 129         }
 130     }
 131 }
 132
 133 // Extract the output string from the given `write_args`.
 134 fn write_output_string(write_args: &[Expr<'_>]) -> Option<String> {
 135     if_chain! {
 136         // Obtain the string that should be printed
 137         if write_args.len() > 1;
 138         if let ExprKind::Call(_, output_args) = write_args[1].kind;
 139         if !output_args.is_empty();
 140         if let ExprKind::AddrOf(BorrowKind::Ref, _, output_string_expr) = output_args[0].kind;
 141         if let ExprKind::Array(string_exprs) = output_string_expr.kind;
 142         // we only want to provide an automatic suggestion for simple (non-format) strings
 143         if string_exprs.len() == 1;
 144         if let ExprKind::Lit(ref lit) = string_exprs[0].kind;
 145         if let LitKind::Str(ref write_output, _) = lit.node;
 146         then {
 147             return Some(write_output.to_string())
 148         }
 149     }
 150     None
 151 }