Modifies the rendering of constant values in rustdoc.

src/librustdoc/html/render/print_item.rs

@@ -1474,34 +1474,27 @@ fn item_constant(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, c: &cle
             typ = c.type_.print(cx),
         );
 
-        // FIXME: The code below now prints
-        //            ` = _; // 100i32`
-        //        if the expression is
-        //            `50 + 50`
-        //        which looks just wrong.
-        //        Should we print
-        //            ` = 100i32;`
-        //        instead?
-
         let value = c.value(tcx);
         let is_literal = c.is_literal(tcx);
         let expr = c.expr(tcx);
-        if value.is_some() || is_literal {
+
+        if is_literal {
             write!(w, " = {expr};", expr = Escape(&expr));
+        } else if let Some(ref value) = value {
+            write!(w, " = {value};", value = Escape(value));
         } else {
             w.write_str(";");
         }
 
-        if !is_literal {
-            if let Some(value) = &value {
-                let value_lowercase = value.to_lowercase();
-                let expr_lowercase = expr.to_lowercase();
+        let value_lowercase = value.as_ref().map(|s| s.to_lowercase());
+        let expr_lowercase = Some(expr.to_lowercase());
 
-                if value_lowercase != expr_lowercase
-                    && value_lowercase.trim_end_matches("i32") != expr_lowercase
-                {
-                    write!(w, " // {value}", value = Escape(value));
-                }
+        if value_lowercase != expr_lowercase
+            && value_lowercase.as_ref().map(|s| s.trim_end_matches("i32"))
+                != expr_lowercase.as_deref()
+        {
+            if let Some(ref value) = value {
+                write!(w, " // {value}", value = Escape(value.as_str()));
             }
         }
     });

src/tools/clippy/clippy_lints/src/invalid_utf8_in_unchecked.rs

@@ -0,0 +1,74 @@
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::{match_function_call, paths};
+use rustc_ast::{BorrowKind, LitKind};
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::source_map::Spanned;
+use rustc_span::Span;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for `std::str::from_utf8_unchecked` with an invalid UTF-8 literal
+    ///
+    /// ### Why is this bad?
+    /// Creating such a `str` would result in undefined behavior
+    ///
+    /// ### Example
+    /// ```rust
+    /// # #[allow(unused)]
+    /// unsafe {
+    ///     std::str::from_utf8_unchecked(b"cl\x82ippy");
+    /// }
+    /// ```
+    #[clippy::version = "1.64.0"]
+    pub INVALID_UTF8_IN_UNCHECKED,
+    correctness,
+    "using a non UTF-8 literal in `std::std::from_utf8_unchecked`"
+}
+declare_lint_pass!(InvalidUtf8InUnchecked => [INVALID_UTF8_IN_UNCHECKED]);
+
+impl<'tcx> LateLintPass<'tcx> for InvalidUtf8InUnchecked {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if let Some([arg]) = match_function_call(cx, expr, &paths::STR_FROM_UTF8_UNCHECKED) {
+            match &arg.kind {
+                ExprKind::Lit(Spanned { node: lit, .. }) => {
+                    if let LitKind::ByteStr(bytes, _) = &lit
+                        && std::str::from_utf8(bytes).is_err()
+                    {
+                        lint(cx, expr.span);
+                    }
+                },
+                ExprKind::AddrOf(BorrowKind::Ref, _, Expr { kind: ExprKind::Array(args), .. }) => {
+                    let elements = args.iter().map(|e|{
+                        match &e.kind {
+                            ExprKind::Lit(Spanned { node: lit, .. }) => match lit {
+                                LitKind::Byte(b) => Some(*b),
+                                #[allow(clippy::cast_possible_truncation)]
+                                LitKind::Int(b, _) => Some(*b as u8),
+                                _ => None
+                            }
+                            _ => None
+                        }
+                    }).collect::<Option<Vec<_>>>();
+
+                    if let Some(elements) = elements
+                        && std::str::from_utf8(&elements).is_err()
+                    {
+                        lint(cx, expr.span);
+                    }
+                }
+                _ => {}
+            }
+        }
+    }
+}
+
+fn lint(cx: &LateContext<'_>, span: Span) {
+    span_lint(
+        cx,
+        INVALID_UTF8_IN_UNCHECKED,
+        span,
+        "non UTF-8 literal in `std::str::from_utf8_unchecked`",
+    );
+}

src/tools/clippy/tests/ui/invalid_utf8_in_unchecked.rs

@@ -0,0 +1,20 @@
+#![warn(clippy::invalid_utf8_in_unchecked)]
+
+fn main() {
+    // Valid
+    unsafe {
+        std::str::from_utf8_unchecked(&[99, 108, 105, 112, 112, 121]);
+        std::str::from_utf8_unchecked(&[b'c', b'l', b'i', b'p', b'p', b'y']);
+        std::str::from_utf8_unchecked(b"clippy");
+
+        let x = 0xA0;
+        std::str::from_utf8_unchecked(&[0xC0, x]);
+    }
+
+    // Invalid
+    unsafe {
+        std::str::from_utf8_unchecked(&[99, 108, 130, 105, 112, 112, 121]);
+        std::str::from_utf8_unchecked(&[b'c', b'l', b'\x82', b'i', b'p', b'p', b'y']);
+        std::str::from_utf8_unchecked(b"cl\x82ippy");
+    }
+}

src/tools/clippy/tests/ui/invalid_utf8_in_unchecked.stderr

@@ -0,0 +1,22 @@
+error: non UTF-8 literal in `std::str::from_utf8_unchecked`
+  --> $DIR/invalid_utf8_in_unchecked.rs:16:9
+   |
+LL |         std::str::from_utf8_unchecked(&[99, 108, 130, 105, 112, 112, 121]);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::invalid-utf8-in-unchecked` implied by `-D warnings`
+
+error: non UTF-8 literal in `std::str::from_utf8_unchecked`
+  --> $DIR/invalid_utf8_in_unchecked.rs:17:9
+   |
+LL |         std::str::from_utf8_unchecked(&[b'c', b'l', b'/x82', b'i', b'p', b'p', b'y']);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: non UTF-8 literal in `std::str::from_utf8_unchecked`
+  --> $DIR/invalid_utf8_in_unchecked.rs:18:9
+   |
+LL |         std::str::from_utf8_unchecked(b"cl/x82ippy");
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+