userdiff-cpp: back out the digit-separators in numbers

The implementation of digit-separating single-quotes introduced a
note-worthy regression: the change of a character literal with a
digit would splice the digit and the closing single-quote. For
example, the change from 'a' to '2' is now tokenized as
'[-a'-]{+2'+} instead of '[-a-]{+2+}'.

The options to fix the regression are:

- Tighten the regular expression such that the single-quote can only
  occur between digits (that would match the official syntax).

- Remove support for digit separators.

I chose to remove support, because

- I have not seen a lot of code make use of digit separators.

- If code does use digit separators, then the numbers are typically
  long. If a change in one of the segments occurs, it is actually
  better visible if only that segment is highlighted as the word
  that changed instead of the whole long number.

This choice does introduce another minor regression, though, which
is highlighted in the test case: when a change occurs in the second
or later segment of a hexadecimal number where the segment begins
with a digit, but also has letters, the segment is mistaken as
consisting of a number and an identifier. I can live with that.

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

t/t4034/cpp/expect

@@ -1,21 +1,21 @@
 <BOLD>diff --git a/pre b/post<RESET>
-<BOLD>index 144cd98..64e78af 100644<RESET>
+<BOLD>index a1a09b7..f1b6f3c 100644<RESET>
 <BOLD>--- a/pre<RESET>
 <BOLD>+++ b/post<RESET>
 <CYAN>@@ -1,30 +1,30 @@<RESET>
 Foo() : x(0<RED>&&1<RESET><GREEN>&42<RESET>) { <RED>foo0<RESET><GREEN>bar<RESET>(x.<RED>find<RESET><GREEN>Find<RESET>); }
 cout<<"Hello World<RED>!<RESET><GREEN>?<RESET>\n"<<endl;
-<GREEN>(<RESET>1 <RED>-<RESET><GREEN>+<RESET>1e10 0xabcdef<GREEN>)<RESET> '<RED>x<RESET><GREEN>.<RESET>'
+<GREEN>(<RESET>1 <RED>-<RESET><GREEN>+<RESET>1e10 0xabcdef<GREEN>)<RESET> '<RED>x<RESET><GREEN>2<RESET>'
 // long double<RESET>
-<RED>3.141'592'653e-10l<RESET><GREEN>3.141'592'654e+10l<RESET>
+<RED>3.141592653e-10l<RESET><GREEN>3.141592654e+10l<RESET>
 // float<RESET>
 <RED>120E5f<RESET><GREEN>120E6f<RESET>
 // hex<RESET>
-<RED>0xdead'beaf<RESET><GREEN>0xdead'Beaf<RESET>+<RED>8ULL<RESET><GREEN>7ULL<RESET>
+<RED>0xdead<RESET><GREEN>0xdeaf<RESET>'1<RED>eaF<RESET><GREEN>eaf<RESET>+<RED>8ULL<RESET><GREEN>7ULL<RESET>
 // octal<RESET>
-<RED>0123'4567<RESET><GREEN>0123'4560<RESET>
+<RED>01234567<RESET><GREEN>01234560<RESET>
 // binary<RESET>
-<RED>0b10'00<RESET><GREEN>0b11'00<RESET>+e1
+<RED>0b1000<RESET><GREEN>0b1100<RESET>+e1
 // expression<RESET>
 1.5-e+<RED>2<RESET><GREEN>3<RESET>+f
 // another one<RESET>

t/t4034/cpp/post

@@ -1,16 +1,16 @@
 Foo() : x(0&42) { bar(x.Find); }
 cout<<"Hello World?\n"<<endl;
-(1 +1e10 0xabcdef) '.'
+(1 +1e10 0xabcdef) '2'
 // long double
-3.141'592'654e+10l
+3.141592654e+10l
 // float
 120E6f
 // hex
-0xdead'Beaf+7ULL
+0xdeaf'1eaf+7ULL
 // octal
-0123'4560
+01234560
 // binary
-0b11'00+e1
+0b1100+e1
 // expression
 1.5-e+3+f
 // another one

t/t4034/cpp/pre

@@ -2,15 +2,15 @@ Foo():x(0&&1){ foo0( x.find); }
 cout<<"Hello World!\n"<<endl;
 1 -1e10 0xabcdef 'x'
 // long double
-3.141'592'653e-10l
+3.141592653e-10l
 // float
 120E5f
 // hex
-0xdead'beaf+8ULL
+0xdead'1eaF+8ULL
 // octal
-0123'4567
+01234567
 // binary
-0b10'00+e1
+0b1000+e1
 // expression
 1.5-e+2+f
 // another one

userdiff.c

@@ -67,11 +67,11 @@ PATTERNS("cpp",
 	 /* identifiers and keywords */
 	 "[a-zA-Z_][a-zA-Z0-9_]*"
 	 /* decimal and octal integers as well as floatingpoint numbers */
-	 "|[0-9][0-9.']*([Ee][-+]?[0-9]+)?[fFlLuU]*"
+	 "|[0-9][0-9.]*([Ee][-+]?[0-9]+)?[fFlLuU]*"
 	 /* hexadecimal and binary integers */
-	 "|0[xXbB][0-9a-fA-F']+[lLuU]*"
+	 "|0[xXbB][0-9a-fA-F]+[lLuU]*"
 	 /* floatingpoint numbers that begin with a decimal point */
-	 "|\\.[0-9][0-9']*([Ee][-+]?[0-9]+)?[fFlL]?"
+	 "|\\.[0-9][0-9]*([Ee][-+]?[0-9]+)?[fFlL]?"
 	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->\\*?|\\.\\*|<=>"),
 PATTERNS("csharp",
 	 /* Keywords */