Handle array to pointer decay for libc members (#176)

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -1944,9 +1944,18 @@ bool Converter::VisitImplicitCastExpr(clang::ImplicitCastExpr *expr) {
       Convert(sub_expr);
       break;
     }
-    Convert(sub_expr);
     bool dest_pointee_const =
         expr->getType()->getPointeeType().isConstQualified();
+    if (const auto *member =
+            clang::dyn_cast<clang::MemberExpr>(sub_expr->IgnoreParenImpCasts());
+        member && IsCharArrayFieldFromLibc(member->getMemberDecl())) {
+      PushParen paren(*this);
+      Convert(sub_expr);
+      StrCat(dest_pointee_const ? ".as_ptr()" : ".as_mut_ptr()");
+      StrCat(keyword::kAs, dest_pointee_const ? "*const u8" : "*mut u8");
+      break;
+    }
+    Convert(sub_expr);
     if (clang::isa<clang::StringLiteral>(sub_expr) ||
         clang::isa<clang::PredefinedExpr>(sub_expr)) {
       StrCat(".as_ptr()");

cpp2rust/converter/converter_lib.cpp

@@ -139,6 +139,16 @@ bool IsCharPointerFieldFromLibc(const clang::ValueDecl *decl) {
       field->getParent()->getLocation());
 }
 
+bool IsCharArrayFieldFromLibc(const clang::ValueDecl *decl) {
+  auto field = clang::dyn_cast<clang::FieldDecl>(decl);
+  if (!field || !field->getType()->isArrayType() ||
+      !field->getType()->getArrayElementTypeNoTypeQual()->isCharType()) {
+    return false;
+  }
+  return field->getASTContext().getSourceManager().isInSystemHeader(
+      field->getParent()->getLocation());
+}
+
 bool IsUserDefinedDecl(const clang::Decl *decl) {
   const auto &ctx = decl->getASTContext();
   const auto &src_mgr = ctx.getSourceManager();

cpp2rust/converter/converter_lib.h

@@ -41,6 +41,8 @@ bool IsInMainFile(const clang::Decl *decl);
 
 bool IsCharPointerFieldFromLibc(const clang::ValueDecl *decl);
 
+bool IsCharArrayFieldFromLibc(const clang::ValueDecl *decl);
+
 bool IsUserDefinedDecl(const clang::Decl *decl);
 
 bool RefersToUserDefinedDecl(const clang::Expr *expr);

tests/unit/libc_char_ptr_field.c

@@ -1,4 +1,5 @@
 // no-compile: refcount
+#include <dirent.h>
 #include <pwd.h>
 #include <unistd.h>
 
@@ -8,5 +9,11 @@ int main(void) {
     return 0;
   }
   char *home = pw->pw_dir;
-  return home == 0;
+
+  struct dirent *d = readdir(opendir("/tmp"));
+  // d_name is a char array which gets translated as i8. We model chars as u8 in
+  // Rust.
+  char *dname = d->d_name;
+
+  return 0;
 }

tests/unit/out/unsafe/libc_char_ptr_field.rs

@@ -17,5 +17,9 @@ unsafe fn main_0() -> i32 {
         return 0;
     }
     let mut home: *mut u8 = ((*pw).pw_dir as *mut u8);
-    return (((home).is_null()) as i32);
+    let mut d: *mut dirent = libc::readdir(libc::opendir(
+        (b"/tmp\0".as_ptr().cast_mut()).cast_const() as *const i8,
+    ));
+    let mut dname: *mut u8 = ((*d).d_name.as_mut_ptr() as *mut u8);
+    return 0;
 }