Uplift temporary-cstring-as-ptr into rustc

Author: nathanwhit

compiler/rustc_lint/src/lib.rs

@@ -49,6 +49,7 @@ mod early;
 mod internal;
 mod late;
 mod levels;
+mod methods;
 mod non_ascii_idents;
 mod nonstandard_style;
 mod passes;
@@ -73,6 +74,7 @@ use rustc_span::Span;
 use array_into_iter::ArrayIntoIter;
 use builtin::*;
 use internal::*;
+use methods::*;
 use non_ascii_idents::*;
 use nonstandard_style::*;
 use redundant_semicolon::*;
@@ -160,6 +162,7 @@ macro_rules! late_lint_passes {
                 ArrayIntoIter: ArrayIntoIter,
                 ClashingExternDeclarations: ClashingExternDeclarations::new(),
                 DropTraitConstraints: DropTraitConstraints,
+                TemporaryCStringAsPtr: TemporaryCStringAsPtr,
             ]
         );
     };

compiler/rustc_lint/src/methods.rs

@@ -0,0 +1,102 @@
+use crate::LateContext;
+use crate::LateLintPass;
+use crate::LintContext;
+use rustc_hir::{Expr, ExprKind};
+use rustc_middle::ty;
+use rustc_span::{
+    symbol::{sym, Symbol, SymbolStr},
+    ExpnKind, Span,
+};
+
+declare_lint! {
+    pub TEMPORARY_CSTRING_AS_PTR,
+    Deny,
+    "detects getting the inner pointer of a temporary `CString`"
+}
+
+declare_lint_pass!(TemporaryCStringAsPtr => [TEMPORARY_CSTRING_AS_PTR]);
+
+/// Returns the method names and argument list of nested method call expressions that make up
+/// `expr`. method/span lists are sorted with the most recent call first.
+pub fn method_calls<'tcx>(
+    expr: &'tcx Expr<'tcx>,
+    max_depth: usize,
+) -> (Vec<Symbol>, Vec<&'tcx [Expr<'tcx>]>, Vec<Span>) {
+    let mut method_names = Vec::with_capacity(max_depth);
+    let mut arg_lists = Vec::with_capacity(max_depth);
+    let mut spans = Vec::with_capacity(max_depth);
+
+    let mut current = expr;
+    for _ in 0..max_depth {
+        if let ExprKind::MethodCall(path, span, args, _) = &current.kind {
+            if args.iter().any(|e| e.span.from_expansion()) {
+                break;
+            }
+            method_names.push(path.ident.name);
+            arg_lists.push(&**args);
+            spans.push(*span);
+            current = &args[0];
+        } else {
+            break;
+        }
+    }
+
+    (method_names, arg_lists, spans)
+}
+
+fn in_macro(span: Span) -> bool {
+    if span.from_expansion() {
+        !matches!(span.ctxt().outer_expn_data().kind, ExpnKind::Desugaring(..))
+    } else {
+        false
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for TemporaryCStringAsPtr {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if in_macro(expr.span) {
+            return;
+        }
+
+        let (method_names, arg_lists, _) = method_calls(expr, 2);
+        let method_names: Vec<SymbolStr> = method_names.iter().map(|s| s.as_str()).collect();
+        let method_names: Vec<&str> = method_names.iter().map(|s| &**s).collect();
+
+        if let ["as_ptr", "unwrap" | "expect"] = method_names.as_slice() {
+            lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0]);
+        }
+    }
+}
+
+fn lint_cstring_as_ptr(
+    cx: &LateContext<'_>,
+    expr: &rustc_hir::Expr<'_>,
+    source: &rustc_hir::Expr<'_>,
+    unwrap: &rustc_hir::Expr<'_>,
+) {
+    let source_type = cx.typeck_results().expr_ty(source);
+    if let ty::Adt(def, substs) = source_type.kind {
+        if cx.tcx.is_diagnostic_item(Symbol::intern("result_type"), def.did) {
+            if let ty::Adt(adt, _) = substs.type_at(0).kind {
+                let path = [
+                    sym::std,
+                    Symbol::intern("ffi"),
+                    Symbol::intern("c_str"),
+                    Symbol::intern("CString"),
+                ];
+                if cx.match_def_path(adt.did, &path) {
+                    cx.struct_span_lint(TEMPORARY_CSTRING_AS_PTR, expr.span, |diag| {
+                        let mut diag = diag
+                            .build("you are getting the inner pointer of a temporary `CString`");
+                        diag.note("that pointer will be invalid outside this expression");
+                        diag.span_help(
+                            unwrap.span,
+                            "assign the `CString` to a variable to extend its lifetime",
+                        );
+                        diag.emit();
+                    });
+                }
+            }
+        }
+    }
+}