userdiff: have 'cpp' hunk header pattern catch more C++ anchor pointsjs/userdiff-cc

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: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

13 files changed, 3 insertions, 17 deletions

diff --git a/t/t4018/cpp-class-constructor b/t/t4018/cpp-class-constructor
index 4c4925c237..ec4f115c25 100644
--- a/t/t4018/cpp-class-constructor
+++ b/t/t4018/cpp-class-constructor
@@ -1,5 +1,4 @@
 Item::Item(int RIGHT)
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-class-constructor-mem-init b/t/t4018/cpp-class-constructor-mem-init
index eec1d7cbf3..49a69f37e1 100644
--- a/t/t4018/cpp-class-constructor-mem-init
+++ b/t/t4018/cpp-class-constructor-mem-init
@@ -2,5 +2,4 @@ Item::Item(int RIGHT) :
 	member(0)
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-class-destructor b/t/t4018/cpp-class-destructor
index 03aa51ca5b..5487665096 100644
--- a/t/t4018/cpp-class-destructor
+++ b/t/t4018/cpp-class-destructor
@@ -1,5 +1,4 @@
 RIGHT::~RIGHT()
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-function-returning-global-type b/t/t4018/cpp-function-returning-global-type
index bff3e5f21c..1084d5990e 100644
--- a/t/t4018/cpp-function-returning-global-type
+++ b/t/t4018/cpp-function-returning-global-type
@@ -1,5 +1,4 @@
 ::Item get::it::RIGHT()
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-function-returning-nested b/t/t4018/cpp-function-returning-nested
index 41700f2c09..d9750aa61a 100644
--- a/t/t4018/cpp-function-returning-nested
+++ b/t/t4018/cpp-function-returning-nested
@@ -1,6 +1,5 @@
 get::Item get::it::RIGHT()
 {
 	ChangeMe;
-	broken;
 }
 
diff --git a/t/t4018/cpp-function-returning-reference b/t/t4018/cpp-function-returning-reference
index 29e2bd4632..01b051df70 100644
--- a/t/t4018/cpp-function-returning-reference
+++ b/t/t4018/cpp-function-returning-reference
@@ -1,5 +1,4 @@
 string& get::it::RIGHT(char *ptr)
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-gnu-style-function b/t/t4018/cpp-gnu-style-function
index d65fc7489c..08c7c7565a 100644
--- a/t/t4018/cpp-gnu-style-function
+++ b/t/t4018/cpp-gnu-style-function
@@ -2,5 +2,4 @@ const char *
 RIGHT(int arg)
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-namespace-definition b/t/t4018/cpp-namespace-definition
index 6b88dd9c3b..6749980241 100644
--- a/t/t4018/cpp-namespace-definition
+++ b/t/t4018/cpp-namespace-definition
@@ -1,5 +1,4 @@
 namespace RIGHT
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-operator-definition b/t/t4018/cpp-operator-definition
index f2bd1678f9..1acd827159 100644
--- a/t/t4018/cpp-operator-definition
+++ b/t/t4018/cpp-operator-definition
@@ -1,5 +1,4 @@
 Value operator+(Value LEFT, Value RIGHT)
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-struct-single-line b/t/t4018/cpp-struct-single-line
index ad6fa8bbe9..a0de5fb800 100644
--- a/t/t4018/cpp-struct-single-line
+++ b/t/t4018/cpp-struct-single-line
@@ -5,4 +5,3 @@ void wrong()
 struct RIGHT_iterator_tag {};
 
 int ChangeMe;
-// broken
diff --git a/t/t4018/cpp-template-function-definition b/t/t4018/cpp-template-function-definition
index a410298b0b..0cdf5ba5bd 100644
--- a/t/t4018/cpp-template-function-definition
+++ b/t/t4018/cpp-template-function-definition
@@ -1,5 +1,4 @@
 template<class T> int RIGHT(T arg)
 {
 	ChangeMe;
-	broken;
 }
diff --git a/t/t4018/cpp-union-definition b/t/t4018/cpp-union-definition
index 133b662258..7ec94df697 100644
--- a/t/t4018/cpp-union-definition
+++ b/t/t4018/cpp-union-definition
@@ -1,5 +1,4 @@
 union RIGHT {
 	double v;
 	int ChangeMe;
-	broken;
 };
diff --git a/userdiff.c b/userdiff.c
index 8830417e3b..fad52d6392 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -125,11 +125,9 @@ PATTERNS("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$",
 	 "\\\\[a-zA-Z@]+|\\\\.|[a-zA-Z0-9\x80-\xff]+"),
 PATTERNS("cpp",
 	 /* Jump targets or access declarations */
-	 "!^[ \t]*[A-Za-z_][A-Za-z_0-9]*:.*$\n"
-	 /* C/++ functions/methods at top level */
-	 "^([A-Za-z_][A-Za-z_0-9]*([ \t*]+[A-Za-z_][A-Za-z_0-9]*([ \t]*::[ \t]*[^[:space:]]+)?){1,}[ \t]*\\([^;]*)$\n"
-	 /* compound type at top level */
-	 "^((struct|class|enum)[^;]*)$",
+	 "!^[ \t]*[A-Za-z_][A-Za-z_0-9]*:[[:space:]]*($|/[/*])\n"
+	 /* functions/methods, variables, and compounds at top level */
+	 "^((::[[:space:]]*)?[A-Za-z_].*)$",
 	 /* -- */
 	 "[a-zA-Z_][a-zA-Z0-9_]*"
 	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lLuU]*"