GenEx: Parse colon after arguments separator colon specially.

The rationale is similar to that in commit b3d8f5da (GenEx: Parse comma
after colon tokens specially, 2012-10-04), in that colon tokens should
not be parsed as identifier-argument delimiters after the first colon.

Source/cmGeneratorExpressionParser.cxx

@@ -14,6 +14,8 @@
 
 #include "cmGeneratorExpressionEvaluator.h"
 
+#include "assert.h"
+
 //----------------------------------------------------------------------------
 cmGeneratorExpressionParser::cmGeneratorExpressionParser(
                       const std::vector<cmGeneratorExpressionToken> &tokens)
@@ -124,6 +126,11 @@ void cmGeneratorExpressionParser::ParseGeneratorExpression(
       parameters.resize(parameters.size() + 1);
       ++this->it;
       }
+    while (this->it->TokenType == cmGeneratorExpressionToken::ColonSeparator)
+      {
+      extendText(*(parameters.end() - 1), this->it);
+      ++this->it;
+      }
     while(this->it->TokenType != cmGeneratorExpressionToken::EndExpression)
       {
       this->ParseContent(*(parameters.end() - 1));
@@ -133,7 +140,7 @@ void cmGeneratorExpressionParser::ParseGeneratorExpression(
         parameters.resize(parameters.size() + 1);
         ++this->it;
         }
-      if (this->it->TokenType == cmGeneratorExpressionToken::ColonSeparator)
+      while (this->it->TokenType == cmGeneratorExpressionToken::ColonSeparator)
         {
         extendText(*(parameters.end() - 1), this->it);
         ++this->it;
@@ -233,7 +240,7 @@ void cmGeneratorExpressionParser::ParseContent(
         }
       else
         {
-        // TODO: Unreachable. Assert?
+          assert(!"Got unexpected syntax token.");
         }
       ++this->it;
       return;

Tests/GeneratorExpression/CMakeLists.txt

@@ -44,6 +44,11 @@ add_custom_target(check ALL
     -Dtest_strequal_one_empty=$<STREQUAL:something,>
     -Dtest_angle_r=$<ANGLE-R>
     -Dtest_comma=$<COMMA>
+    -Dtest_colons_1=$<1::>
+    -Dtest_colons_2=$<1:::>
+    -Dtest_colons_3=$<1:Qt5::Core>
+    -Dtest_colons_4=$<1:C:\\CMake>
+    -Dtest_colons_5=$<1:C:/CMake>
     -P ${CMAKE_CURRENT_SOURCE_DIR}/check.cmake
   COMMAND ${CMAKE_COMMAND} -E echo "check done"
   VERBATIM

Tests/GeneratorExpression/check.cmake

@@ -45,3 +45,8 @@ check(test_strequal_both_empty "1")
 check(test_strequal_one_empty "0")
 check(test_angle_r ">")
 check(test_comma ",")
+check(test_colons_1 ":")
+check(test_colons_2 "::")
+check(test_colons_3 "Qt5::Core")
+check(test_colons_4 "C:\\\\CMake")
+check(test_colons_5 "C:/CMake")