[clang-tidy] add new checker for string literal with NUL character.

Summary:
This patch adds the support for detecting suspicious string
literals and their //incorrect// usage.

The following example shows a incorrect character escaping leading 
to an embedded NUL character. 
```
  std::string str = "\0x42";   // Should be "\x42".
```

The patch also add detection of truncated literal when a literal
is passed to a string constructor.

Reviewers: hokein, alexfh

Subscribers: LegalizeAdulthood, bcraig, Eugene.Zelenko, bkramer, cfe-commits

Differential Revision: http://reviews.llvm.org/D18783

llvm-svn: 265691

1 files changed, 38 insertions, 0 deletions

diff --git a/clang-tools-extra/docs/clang-tidy/checks/misc-string-literal-with-embedded-nul.rst b/clang-tools-extra/docs/clang-tidy/checks/misc-string-literal-with-embedded-nul.rst
new file mode 100644
index 00000000000..3661218acef
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/misc-string-literal-with-embedded-nul.rst
@@ -0,0 +1,38 @@
+.. title:: clang-tidy - misc-string-literal-with-embedded-nul
+
+misc-string-literal-with-embedded-nul
+=====================================
+
+Finds occurences of string literal with embedded NUL character and validates
+their usage.
+
+
+Invalid escaping
+^^^^^^^^^^^^^^^^
+
+Special characters can be escaped within a string literal by using their
+hexadecimal encoding like ``\x42``. A common mistake is to escape them
+like this ``\0x42`` where the ``\0`` stands for the NUL character.
+
+.. code:: c++
+
+  const char* Example[] = "Invalid character: \0x12 should be \x12";
+  const char* Bytes[] = "\x03\0x02\0x01\0x00\0xFF\0xFF\0xFF";
+
+
+Truncated literal
+^^^^^^^^^^^^^^^^^
+
+String-like classes can manipulate strings with embedded NUL as they are
+keeping track of the bytes and the length. This is not the case for a
+``char*`` (NUL-terminated) string.
+
+A common mistake is to pass a string-literal with embedded NUL to a string
+constructor expecting a NUL-terminated string. The bytes after the first NUL
+character are truncated.
+
+.. code:: c++
+
+  std::string str("abc\0def");  // "def" is truncated
+  str += "\0";                  // This statement is doing nothing
+  if (str == "\0abc") return;   // This expression is always true