Coverity issue (FORWARD_NULL) in lexer(std::istream& s)

[darklukee]

Coverity found an issue in lexer(std::istream& s):

1. assign_zero: Assigning: this->m_start = NULL.

7618        explicit lexer(std::istream& s)
7619            : m_stream(&s), m_line_buffer()
7620        {
7621            // fill buffer

CID 1077412 (#1 of 3): Explicit null dereferenced (FORWARD_NULL)
2. var_deref_model: fill_line_buffer dereferences null this->m_start.

7622 fill_line_buffer();

[nlohmann]

I'll have a look at this. By the way, how did you get Coverity to run? I currently have a problem with this, see #299.

[darklukee]

It was run locally on build server. I didn't set it up and I don't have access to configuration so I can't help you here. Coverity version used: 8.0.0.

But you are doing some weird steps in COVERITY_SCAN_BUILD_COMMAND_PREPEND. I would look into it.

[nlohmann]

Issue #299 seems to be fixed. I could run a Coverity analysis and I found the same error:

** CID 154530:  Null pointer dereferences  (FORWARD_NULL)
/src/json.hpp: 9124 in nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long, unsigned long, double, std::__1::allocator>::lexer::lexer(std::__1::basic_istream<char, std::__1::char_traits<char>> &)()

________________________________________________________________________________________________________
*** CID 154530:  Null pointer dereferences  (FORWARD_NULL)
/src/json.hpp: 9124 in nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long, unsigned long, double, std::__1::allocator>::lexer::lexer(std::__1::basic_istream<char, std::__1::char_traits<char>> &)()
9118             std::istream* m_stream = nullptr;
9119             /// line buffer buffer for m_stream
9120             string_t m_line_buffer {};
9121             /// the buffer pointer
9122             const lexer_char_t* m_content = nullptr;
9123             /// pointer to the beginning of the current symbol
   CID 154530:  Null pointer dereferences  (FORWARD_NULL)
   Assigning: "this->m_start" = "NULL".
9124             const lexer_char_t* m_start = nullptr;
9125             /// pointer for backtracking information
9126             const lexer_char_t* m_marker = nullptr;
9127             /// pointer to the current symbol
9128             const lexer_char_t* m_cursor = nullptr;
9129             /// pointer to the end of the buffer

However, I have yet to understand the error.

[nlohmann]

More details:

[nlohmann]

This is a false positive:

• When lexer(std::istream& s) is called, a pointer to s is stored in m_stream. m_stream cannot be nullptr when fill_line_buffer is called from lexer(std::istream& s).
• m_stream == NULL is the precondition (1.) of Coverity.

Nevertheless, I shall add an assertion before the append call.