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