suspicious_leading_zero lint

Author: GrigorenkoPV

compiler/rustc_lint/messages.ftl

@@ -778,6 +778,9 @@ lint_suspicious_double_ref_clone =
 lint_suspicious_double_ref_deref =
     using `.deref()` on a double reference, which returns `{$ty}` instead of dereferencing the inner type
 
+lint_suspicious_leading_zero = TODO
+    .suggestion = TODO
+
 lint_tail_expr_drop_order = these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021
     .label = these values have significant drop implementation and will observe changes in drop order under Edition 2024
 

compiler/rustc_lint/src/builtin.rs

@@ -66,7 +66,7 @@ use crate::lints::{
     BuiltinTrivialBounds, BuiltinTypeAliasBounds, BuiltinUngatedAsyncFnTrackCaller,
     BuiltinUnpermittedTypeInit, BuiltinUnpermittedTypeInitSub, BuiltinUnreachablePub,
     BuiltinUnsafe, BuiltinUnstableFeatures, BuiltinUnusedDocComment, BuiltinUnusedDocCommentSub,
-    BuiltinWhileTrue, InvalidAsmLabel,
+    BuiltinWhileTrue, InvalidAsmLabel, SuspiciousLeadingZero,
 };
 use crate::nonstandard_style::{MethodLateContext, method_context};
 use crate::{
@@ -3035,3 +3035,33 @@ impl EarlyLintPass for SpecialModuleName {
         }
     }
 }
+
+declare_lint! {
+    /// TODO
+    pub SUSPICIOUS_LEADING_ZERO,
+    Warn,
+    "TODO",
+}
+
+declare_lint_pass!(LeadingZero => [SUSPICIOUS_LEADING_ZERO]);
+
+impl EarlyLintPass for LeadingZero {
+    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
+        if let ast::ExprKind::Lit(literal) = expr.kind
+            && let token::Lit { kind: token::LitKind::Integer, symbol, suffix: _ } = literal
+            && let s = symbol.as_str()
+            && s.starts_with('0')
+            && !["0x", "0b", "0o"].into_iter().any(|prefix| s.starts_with(prefix))
+            // Has some other digits after the leading 0 and all those digits are octal:
+            && let Some(true) = s.bytes().skip(1).try_fold(false, |res, c| match c {
+                b'0'..=b'7' => Some(true),
+                b'8' | b'9' => None,
+                ..=b'/' | b':'.. => Some(res),
+            })
+        {
+            let lit_span = expr.span;
+            let span = lit_span.with_hi(lit_span.lo() + BytePos(1));
+            cx.emit_span_lint(SUSPICIOUS_LEADING_ZERO, span, SuspiciousLeadingZero { span });
+        }
+    }
+}

compiler/rustc_lint/src/lib.rs

@@ -187,6 +187,7 @@ early_lint_methods!(
             UnusedDocComment: UnusedDocComment,
             Expr2024: Expr2024,
             Precedence: Precedence,
+            LeadingZero: LeadingZero,
         ]
     ]
 );

compiler/rustc_lint/src/lints.rs

@@ -3061,3 +3061,10 @@ pub(crate) enum MutRefSugg {
 #[derive(LintDiagnostic)]
 #[diag(lint_unqualified_local_imports)]
 pub(crate) struct UnqualifiedLocalImportsDiag {}
+
+#[derive(LintDiagnostic)]
+#[diag(lint_suspicious_leading_zero)]
+pub(crate) struct SuspiciousLeadingZero {
+    #[suggestion(code = "0o", style = "verbose", applicability = "maybe-incorrect")]
+    pub span: Span,
+}

tests/ui/lint/suspicious-leading-zero.rs

@@ -0,0 +1,7 @@
+#![deny(suspicious_leading_zero)]
+
+fn main() {
+    let _ = 0111; //~ ERROR [suspicious_leading_zero]
+    let _ = 0007; //~ ERROR [suspicious_leading_zero]
+    let _ = 0008;
+}

tests/ui/lint/suspicious-leading-zero.stderr

@@ -0,0 +1,29 @@
+error: TODO
+  --> $DIR/suspicious-leading-zero.rs:4:13
+   |
+LL |     let _ = 0111;
+   |             ^
+   |
+note: the lint level is defined here
+  --> $DIR/suspicious-leading-zero.rs:1:9
+   |
+LL | #![deny(suspicious_leading_zero)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+help: TODO
+   |
+LL |     let _ = 0o111;
+   |             ~~
+
+error: TODO
+  --> $DIR/suspicious-leading-zero.rs:5:13
+   |
+LL |     let _ = 0007;
+   |             ^
+   |
+help: TODO
+   |
+LL |     let _ = 0o007;
+   |             ~~
+
+error: aborting due to 2 previous errors
+