Fix potential infinite loops in generators combined with section filter

The problem was that under specific circumstances, namely that none
of their children progressed, `GeneratorTracker` will not progress.
This was changed recently, to allow for code like this, where a
`SECTION` follows a `GENERATE` at the same level:

```cpp
SECTION("A") {}
auto a = GENERATE(1, 2);
SECTION("B") {}
```

However, this interacted badly with `SECTION` filters (`-c foo`),
as they could deactivate all `SECTION`s below a generator, and thus
stop it from progressing forever. This commit makes GeneratorTracker
check whether there are any filters active, and if they are, it checks
whether its section-children can ever run.

Fixes #2025

projects/CMakeLists.txt

@@ -419,6 +419,33 @@ set_tests_properties(FilteredSection-1 PROPERTIES FAIL_REGULAR_EXPRESSION "No te
 add_test(NAME FilteredSection-2 COMMAND $<TARGET_FILE:SelfTest> \#1394\ nested -c NestedRunSection -c s1)
 set_tests_properties(FilteredSection-2 PROPERTIES FAIL_REGULAR_EXPRESSION "No tests ran")
 
+add_test(
+  NAME
+    FilteredSection::GeneratorsDontCauseInfiniteLoop-1
+  COMMAND
+    $<TARGET_FILE:SelfTest> "#2025: original repro" -c "fov_0"
+)
+set_tests_properties(FilteredSection::GeneratorsDontCauseInfiniteLoop-1
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "inside with fov: 0" # This should happen
+    FAIL_REGULAR_EXPRESSION "inside with fov: 1" # This would mean there was no filtering
+)
+
+# GENERATE between filtered sections (both are selected)
+add_test(
+  NAME
+    FilteredSection::GeneratorsDontCauseInfiniteLoop-2
+  COMMAND
+    $<TARGET_FILE:SelfTest> "#2025: same-level sections"
+    -c "A"
+    -c "B"
+)
+set_tests_properties(FilteredSection::GeneratorsDontCauseInfiniteLoop-2
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "All tests passed \\(4 assertions in 1 test case\\)"
+)
+
+
 # AppVeyor has a Python 2.7 in path, but doesn't have .py files as autorunnable
 add_test(NAME ApprovalTests COMMAND ${PYTHON_EXECUTABLE} ${CATCH_DIR}/scripts/approvalTests.py $<TARGET_FILE:SelfTest>)
 set_tests_properties(ApprovalTests PROPERTIES FAIL_REGULAR_EXPRESSION "Results differed")

projects/SelfTest/UsageTests/Tricky.tests.cpp

@@ -402,3 +402,28 @@ TEST_CASE("#1514: stderr/stdout is not captured in tests aborted by an exception
     // FAIL aborts the test by throwing a Catch exception
     FAIL("1514");
 }
+
+
+TEST_CASE( "#2025: -c shouldn't cause infinite loop", "[sections][generators][regression][.approvals]" ) {
+    SECTION( "Check cursor from buffer offset" ) {
+        auto bufPos = GENERATE_REF( range( 0, 44 ) );
+        WHEN( "Buffer position is " << bufPos ) { REQUIRE( 1 == 1 ); }
+    }
+}
+
+TEST_CASE("#2025: original repro", "[sections][generators][regression][.approvals]") {
+    auto fov = GENERATE(true, false);
+    DYNAMIC_SECTION("fov_" << fov) {
+        std::cout << "inside with fov: " << fov << '\n';
+    }
+}
+
+TEST_CASE("#2025: same-level sections", "[sections][generators][regression][.approvals]") {
+    SECTION("A") {
+        SUCCEED();
+    }
+    auto i = GENERATE(1, 2, 3);
+    SECTION("B") {
+        REQUIRE(i < 4);
+    }
+}