New upstream version 1.52.1+dfsg1

[rustc.git] / src / tools / clippy / clippy_lints / src / duration_subsec.rs

diff --git a/src/tools/clippy/clippy_lints/src/duration_subsec.rs b/src/tools/clippy/clippy_lints/src/duration_subsec.rs
new file mode 100644 (file)
index 0000000..c0529a3
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/duration_subsec.rs
@@ -0,0 +1,71 @@
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::source_map::Spanned;
+
+use crate::consts::{constant, Constant};
+use crate::utils::paths;
+use crate::utils::{match_type, snippet_with_applicability, span_lint_and_sugg};
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for calculation of subsecond microseconds or milliseconds
+    /// from other `Duration` methods.
+    ///
+    /// **Why is this bad?** It's more concise to call `Duration::subsec_micros()` or
+    /// `Duration::subsec_millis()` than to calculate them.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// # use std::time::Duration;
+    /// let dur = Duration::new(5, 0);
+    ///
+    /// // Bad
+    /// let _micros = dur.subsec_nanos() / 1_000;
+    /// let _millis = dur.subsec_nanos() / 1_000_000;
+    ///
+    /// // Good
+    /// let _micros = dur.subsec_micros();
+    /// let _millis = dur.subsec_millis();
+    /// ```
+    pub DURATION_SUBSEC,
+    complexity,
+    "checks for calculation of subsecond microseconds or milliseconds"
+}
+
+declare_lint_pass!(DurationSubsec => [DURATION_SUBSEC]);
+
+impl<'tcx> LateLintPass<'tcx> for DurationSubsec {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if_chain! {
+            if let ExprKind::Binary(Spanned { node: BinOpKind::Div, .. }, ref left, ref right) = expr.kind;
+            if let ExprKind::MethodCall(ref method_path, _ , ref args, _) = left.kind;
+            if match_type(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), &paths::DURATION);
+            if let Some((Constant::Int(divisor), _)) = constant(cx, cx.typeck_results(), right);
+            then {
+                let suggested_fn = match (method_path.ident.as_str().as_ref(), divisor) {
+                    ("subsec_micros", 1_000) | ("subsec_nanos", 1_000_000) => "subsec_millis",
+                    ("subsec_nanos", 1_000) => "subsec_micros",
+                    _ => return,
+                };
+                let mut applicability = Applicability::MachineApplicable;
+                span_lint_and_sugg(
+                    cx,
+                    DURATION_SUBSEC,
+                    expr.span,
+                    &format!("calling `{}()` is more concise than this calculation", suggested_fn),
+                    "try",
+                    format!(
+                        "{}.{}()",
+                        snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
+                        suggested_fn
+                    ),
+                    applicability,
+                );
+            }
+        }
+    }
+}