Add implementation and tests for literal checking in print/println format args
This commit is contained in:
Michael Recachinas
parent
83e210935d
commit
62220abfa6
@ -78,12 +78,28 @@
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"use of `Debug`-based formatting"
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}
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/// **What it does:** This lint warns about the use of literals as `print!`/`println!` args.
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///
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/// **Why is this bad?** Using literals as `println!` args is inefficient
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/// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
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/// (i.e., just put the literal in the format string)
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///
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/// **Example:**
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/// ```rust
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/// println!("{}", "foo");
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/// ```
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declare_lint! {
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pub PRINT_LITERAL,
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Allow,
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"printing a literal with a format string"
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}
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#[derive(Copy, Clone, Debug)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(PRINT_WITH_NEWLINE, PRINTLN_EMPTY_STRING, PRINT_STDOUT, USE_DEBUG)
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lint_array!(PRINT_WITH_NEWLINE, PRINTLN_EMPTY_STRING, PRINT_STDOUT, USE_DEBUG, PRINT_LITERAL)
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}
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}
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@ -107,6 +123,10 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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span_lint(cx, PRINT_STDOUT, span, &format!("use of `{}!`", name));
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// Check for literals in the print!/println! args
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// Also, ensure the format string is `{}` with no special options, like `{:X}`
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check_print_args_for_literal(cx, args);
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if_chain! {
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// ensure we're calling Arguments::new_v1
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if args.len() == 1;
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@ -146,6 +166,49 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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}
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}
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// Check for literals in print!/println! args
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// ensuring the format string for the literal is `DISPLAY_FMT_METHOD`
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// e.g., `println!("... {} ...", "foo")`
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// ^ literal in `println!`
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fn check_print_args_for_literal<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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args: &HirVec<Expr>
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) {
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if_chain! {
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if args.len() == 1;
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if let ExprCall(_, ref args_args) = args[0].node;
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if args_args.len() > 1;
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if let ExprAddrOf(_, ref match_expr) = args_args[1].node;
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if let ExprMatch(ref matchee, ref arms, _) = match_expr.node;
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if let ExprTup(ref tup) = matchee.node;
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if arms.len() == 1;
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if let ExprArray(ref arm_body_exprs) = arms[0].body.node;
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then {
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// it doesn't matter how many args there are in the `print!`/`println!`,
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// if there's one literal, we should warn the user
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for (idx, tup_arg) in tup.iter().enumerate() {
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if_chain! {
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// first, make sure we're dealing with a literal (i.e., an ExprLit)
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if let ExprAddrOf(_, ref tup_val) = tup_arg.node;
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if let ExprLit(_) = tup_val.node;
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// next, check the corresponding match arm body to ensure
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// this is "{}", or DISPLAY_FMT_METHOD
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if let ExprCall(_, ref body_args) = arm_body_exprs[idx].node;
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if body_args.len() == 2;
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if let ExprPath(ref body_qpath) = body_args[1].node;
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if let Some(fun_def_id) = opt_def_id(resolve_node(cx, body_qpath, body_args[1].hir_id));
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if match_def_path(cx.tcx, fun_def_id, &paths::DISPLAY_FMT_METHOD) ||
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match_def_path(cx.tcx, fun_def_id, &paths::DEBUG_FMT_METHOD);
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then {
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span_lint(cx, PRINT_LITERAL, tup_val.span, "printing a literal with an empty format string");
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}
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}
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}
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}
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}
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}
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// Check for print!("... \n", ...).
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fn check_print<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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32
tests/ui/print_literal.rs
Normal file
32
tests/ui/print_literal.rs
Normal file
@ -0,0 +1,32 @@
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#![warn(print_literal)]
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fn main() {
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// these should be fine
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print!("Hello");
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println!("Hello");
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let world = "world";
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println!("Hello {}", world);
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println!("3 in hex is {:X}", 3);
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// these should throw warnings
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print!("Hello {}", "world");
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println!("Hello {} {}", world, "world");
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println!("Hello {}", "world");
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println!("10 / 4 is {}", 2.5);
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println!("2 + 1 = {}", 3);
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println!("2 + 1 = {:.4}", 3);
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println!("2 + 1 = {:5.4}", 3);
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println!("Debug test {:?}", "hello, world");
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// positional args don't change the fact
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// that we're using a literal -- this should
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// throw a warning
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println!("{0} {1}", "hello", "world");
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println!("{1} {0}", "hello", "world");
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// named args shouldn't change anything either
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println!("{foo} {bar}", foo="hello", bar="world");
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println!("{bar} {foo}", foo="hello", bar="world");
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}
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100
tests/ui/print_literal.stderr
Normal file
100
tests/ui/print_literal.stderr
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@ -0,0 +1,100 @@
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:14:24
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14 | print!("Hello {}", "world");
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| ^^^^^^^
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= note: `-D print-literal` implied by `-D warnings`
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:15:36
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15 | println!("Hello {} {}", world, "world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:16:26
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16 | println!("Hello {}", "world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:17:30
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17 | println!("10 / 4 is {}", 2.5);
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| ^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:18:28
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18 | println!("2 + 1 = {}", 3);
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| ^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:19:31
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19 | println!("2 + 1 = {:.4}", 3);
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| ^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:20:32
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20 | println!("2 + 1 = {:5.4}", 3);
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| ^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:21:33
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21 | println!("Debug test {:?}", "hello, world");
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| ^^^^^^^^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:26:25
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26 | println!("{0} {1}", "hello", "world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:26:34
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26 | println!("{0} {1}", "hello", "world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:27:25
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27 | println!("{1} {0}", "hello", "world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:27:34
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27 | println!("{1} {0}", "hello", "world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:30:33
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30 | println!("{foo} {bar}", foo="hello", bar="world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:30:46
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30 | println!("{foo} {bar}", foo="hello", bar="world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:31:33
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31 | println!("{bar} {foo}", foo="hello", bar="world");
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| ^^^^^^^
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error: printing a literal with an empty format string
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--> $DIR/print_literal.rs:31:46
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31 | println!("{bar} {foo}", foo="hello", bar="world");
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| ^^^^^^^
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error: aborting due to 16 previous errors
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