• Johannes Sixt's avatar
    userdiff: have 'cpp' hunk header pattern catch more C++ anchor points · 8a2e8da3
    Johannes Sixt authored
    The hunk header pattern 'cpp' is intended for C and C++ source code, but
    it is actually not particularly useful for the latter, and even misses
    some use-cases for the former.
    
    The parts of the pattern have the following flaws:
    
    - The first part matches an identifier followed immediately by a colon
      and arbitrary text and is intended to reject goto labels and C++
      access specifiers (public, private, protected). But this pattern also
      rejects C++ constructs, which look like this:
    
        MyClass::MyClass()
        MyClass::~MyClass()
        MyClass::Item MyClass::Find(...
    
    - The second part matches an identifier followed by a list of qualified
      names (i.e. identifiers separated by the C++ scope operator '::')
      separated by space or '*' followed by an opening parenthesis (with
      space between the tokens). It matches function declarations like
    
        struct item* get_head(...
        int Outer::Inner::Func(...
    
      Since the pattern requires at least two identifiers, GNU-style
      function definitions are ignored:
    
        void
        func(...
    
      Moreover, since the pattern does not allow punctuation other than '*',
      the following C++ constructs are not recognized:
    
      . template definitions:
          template<class T> int func(T arg)
    
      . functions returning references:
          const string& get_message()
    
      . functions returning templated types:
          vector<int> foo()
    
      . operator definitions:
          Value operator+(Value l, Value r)
    
    - The third part of the pattern finally matches compound definitions.
      But it forgets about unions and namespaces, and also skips single-line
      definitions
    
        struct random_iterator_tag {};
    
      because no semicolon can occur on the line.
    
    Change the first pattern to require a colon at the end of the line
    (except for trailing space and comments), so that it does not reject
    constructor or destructor definitions.
    
    Notice that all interesting anchor points begin with an identifier or
    keyword. But since there is a large variety of syntactical constructs
    after the first "word", the simplest is to require only this word and
    accept everything else. Therefore, this boils down to a line that begins
    with a letter or underscore (optionally preceded by the C++ scope
    operator '::' to accept functions returning a type anchored at the
    global namespace). Replace the second and third part by a single pattern
    that picks such a line.
    
    This has the following desirable consequence:
    
    - All constructs mentioned above are recognized.
    
    and the following likely desirable consequences:
    
    - Definitions of global variables and typedefs are recognized:
    
        int num_entries = 0;
        extern const char* help_text;
        typedef basic_string<wchar_t> wstring;
    
    - Commonly used marco-ized boilerplate code is recognized:
    
        BEGIN_MESSAGE_MAP(CCanvas,CWnd)
        Q_DECLARE_METATYPE(MyStruct)
        PATTERNS("tex",...)
    
      (The last one is from this very patch.)
    
    but also the following possibly undesirable consequence:
    
    - When a label is not on a line by itself (except for a comment) it is
      no longer rejected, but can appear as a hunk header if it occurs at
      the beginning of a line:
    
        next:;
    
    IMO, the benefits of the change outweigh the (possible) regressions by a
    large margin.
    Signed-off-by: default avatarJohannes Sixt <j6t@kdbg.org>
    Signed-off-by: default avatarJunio C Hamano <gitster@pobox.com>
    8a2e8da3
userdiff.c 9.15 KB