Merge commit 'ea16f7d9dbad' from llvm.org/main into next

git apple-llvm automerger · git apple-llvm automerger · commit 70e327ec1763 · 2025-11-13T08:43:10.000-08:00
diff --git a/libcxx/include/fstream b/libcxx/include/fstream
@@ -315,8 +315,14 @@ protected:
         traits_type::copy(__str, this->gptr(), __n);
         this->__gbump_ptrdiff(__n);
       }
-      if (__len - __n >= this->egptr() - this->eback())
-        return std::fread(__str + __n, sizeof(char_type), __len - __n, __file_);
+      const streamsize __remainder    = __len - __n;
+      const streamsize __buffer_space = this->egptr() - this->eback();
+
+      if (__remainder >= __buffer_space)
+        return std::fread(__str + __n, sizeof(char_type), __remainder, __file_) + __n;
+      else if (__remainder > 0)
+        return basic_streambuf<_CharT, _Traits>::xsgetn(__str + __n, __remainder) + __n;
+      return __n;
     }
     return basic_streambuf<_CharT, _Traits>::xsgetn(__str, __len);
   }

Original file line number	Diff line number	Diff line change
`@@ -315,8 +315,14 @@ protected:`
`315`	`315`	`traits_type::copy(__str, this->gptr(), __n);`
`316`	`316`	`this->__gbump_ptrdiff(__n);`
`317`	`317`	`}`
`318`		`- if (__len - __n >= this->egptr() - this->eback())`
`319`		`- return std::fread(__str + __n, sizeof(char_type), __len - __n, __file_);`
	`318`	`+ const streamsize __remainder = __len - __n;`
	`319`	`+ const streamsize __buffer_space = this->egptr() - this->eback();`
	`320`	`+`
	`321`	`+ if (__remainder >= __buffer_space)`
	`322`	`+ return std::fread(__str + __n, sizeof(char_type), __remainder, __file_) + __n;`
	`323`	`+ else if (__remainder > 0)`
	`324`	`+ return basic_streambuf<_CharT, _Traits>::xsgetn(__str + __n, __remainder) + __n;`
	`325`	`+ return __n;`
`320`	`326`	`}`
`321`	`327`	`return basic_streambuf<_CharT, _Traits>::xsgetn(__str, __len);`
`322`	`328`	`}`