Add chained comparisons, implements P0515R0 3.3 and P0893

Now `min < index <= max` work and do the right thing (in today's C++ they silently compile but are a bug, even if the programmer intended the meaningful chained comparison)
And nonsense chains like `a >= b < c` are disallowed (in today's C++ they silently compile but are a bug, and conceptually meaningless)

regression-tests/pure2-chained-comparisons.cpp2

@@ -0,0 +1,16 @@
+main: () -> int = {
+    std::cout << std::boolalpha;
+    i:=0; while i<3 next i++ {
+        j:=0; while j<3 next j++ {
+            k:=0; while k<3 next k++ {
+                std::cout
+                    << i << " "
+                    << j << " "
+                    << k << ": "
+                    << (i == j == k) << " "
+                    << (i <  j <= k) << " "
+                    << (i >= j >  k) << "\n";
+            }
+        }
+    }
+}

regression-tests/test-results/clang-12/pure2-chained-comparisons.cpp.execution

@@ -0,0 +1,27 @@
+0 0 0: true false false
+0 0 1: false false false
+0 0 2: false false false
+0 1 0: false false false
+0 1 1: false true false
+0 1 2: false true false
+0 2 0: false false false
+0 2 1: false false false
+0 2 2: false true false
+1 0 0: false false false
+1 0 1: false false false
+1 0 2: false false false
+1 1 0: false false true
+1 1 1: true false false
+1 1 2: false false false
+1 2 0: false false false
+1 2 1: false false false
+1 2 2: false true false
+2 0 0: false false false
+2 0 1: false false false
+2 0 2: false false false
+2 1 0: false false true
+2 1 1: false false false
+2 1 2: false false false
+2 2 0: false false true
+2 2 1: false false true
+2 2 2: true false false

regression-tests/test-results/gcc-10/pure2-chained-comparisons.cpp.execution

@@ -0,0 +1,27 @@
+0 0 0: true false false
+0 0 1: false false false
+0 0 2: false false false
+0 1 0: false false false
+0 1 1: false true false
+0 1 2: false true false
+0 2 0: false false false
+0 2 1: false false false
+0 2 2: false true false
+1 0 0: false false false
+1 0 1: false false false
+1 0 2: false false false
+1 1 0: false false true
+1 1 1: true false false
+1 1 2: false false false
+1 2 0: false false false
+1 2 1: false false false
+1 2 2: false true false
+2 0 0: false false false
+2 0 1: false false false
+2 0 2: false false false
+2 1 0: false false true
+2 1 1: false false false
+2 1 2: false false false
+2 2 0: false false true
+2 2 1: false false true
+2 2 2: true false false

regression-tests/test-results/mixed-captures-in-expressions-and-postconditions.cpp

@@ -32,7 +32,7 @@ std::vector<int> vec {};
 auto insert_at(cpp2::in<int> where, cpp2::in<int> val) -> void
 {   
     cpp2::Default.expects(cpp2::cmp_less_eq(0,where) && cpp2::cmp_less_eq(where,CPP2_UFCS_0(ssize, vec)), "");
-    auto post_21_5 = cpp2::finally_success([_0 = CPP2_UFCS_0(ssize, vec)]{cpp2::Default.expects(CPP2_UFCS_0(ssize, vec) == _0 + 1, "");} );
+    auto post_21_5 = cpp2::finally_success([_0 = CPP2_UFCS_0(ssize, vec)]{cpp2::Default.expects(CPP2_UFCS_0(ssize, vec)==_0 + 1, "");} );
 #line 21 "mixed-captures-in-expressions-and-postconditions.cpp2"
 
 

regression-tests/test-results/mixed-initialization-safety-3.cpp

@@ -49,5 +49,5 @@ auto print_decorated(auto const& x) -> void { std::cout << ">> [" << x << "]\n";
 
 // for test determinism, force "xyzzy" branch
 // the standard mandates that std::mt19937()() == 3499211612
-[[nodiscard]] auto flip_a_coin() -> bool { return std::mt19937()() % 2 == 0; }
+[[nodiscard]] auto flip_a_coin() -> bool { return std::mt19937()() % 2==0; }
 

regression-tests/test-results/mixed-parameter-passing-with-forward.cpp

@@ -55,7 +55,7 @@ requires std::is_same_v<CPP2_TYPEOF(e), std::string>
 
     copy_from(z);
 
-    if (std::time(nullptr) % 2 == 0) {
+    if (std::time(nullptr) % 2==0) {
         copy_from(std::move(z));
     }
 

regression-tests/test-results/mixed-parameter-passing.cpp

@@ -50,7 +50,7 @@ auto parameter_styles(
 
     copy_from(z);
 
-    if (std::time(nullptr) % 2 == 0) {
+    if (std::time(nullptr) % 2==0) {
         copy_from(std::move(z));
     }
 

regression-tests/test-results/mixed-postexpression-with-capture.cpp

@@ -27,7 +27,7 @@ std::vector<int> vec {};
 auto insert_at(cpp2::in<int> where, cpp2::in<int> val) -> void
 {   
     cpp2::Default.expects(cpp2::cmp_less_eq(0,where) && cpp2::cmp_less_eq(where,CPP2_UFCS_0(ssize, vec)), "");
-    auto post_16_5 = cpp2::finally_success([_0 = CPP2_UFCS_0(size, vec)]{cpp2::Default.expects(CPP2_UFCS_0(size, vec) == _0 + 1, "");} );
+    auto post_16_5 = cpp2::finally_success([_0 = CPP2_UFCS_0(size, vec)]{cpp2::Default.expects(CPP2_UFCS_0(size, vec)==_0 + 1, "");} );
 #line 16 "mixed-postexpression-with-capture.cpp2"
 
 

regression-tests/test-results/msvc-2022/pure2-chained-comparisons.cpp.execution

@@ -0,0 +1,27 @@
+0 0 0: true false false
+0 0 1: false false false
+0 0 2: false false false
+0 1 0: false false false
+0 1 1: false true false
+0 1 2: false true false
+0 2 0: false false false
+0 2 1: false false false
+0 2 2: false true false
+1 0 0: false false false
+1 0 1: false false false
+1 0 2: false false false
+1 1 0: false false true
+1 1 1: true false false
+1 1 2: false false false
+1 2 0: false false false
+1 2 1: false false false
+1 2 2: false true false
+2 0 0: false false false
+2 0 1: false false false
+2 0 2: false false false
+2 1 0: false false true
+2 1 1: false false false
+2 1 2: false false false
+2 2 0: false false true
+2 2 1: false false true
+2 2 2: true false false

regression-tests/test-results/msvc-2022/pure2-chained-comparisons.cpp.output

@@ -0,0 +1 @@
+pure2-chained-comparisons.cpp

regression-tests/test-results/pure2-chained-comparisons.cpp

@@ -0,0 +1,28 @@
+// ----- Cpp2 support -----
+#define CPP2_USE_MODULES         Yes
+#include "cpp2util.h"
+
+
+#line 1 "pure2-chained-comparisons.cpp2"
+[[nodiscard]] auto main() -> int;
+
+//=== Cpp2 definitions ==========================================================
+
+#line 1 "pure2-chained-comparisons.cpp2"
+[[nodiscard]] auto main() -> int{
+    std::cout << std::boolalpha;
+    auto i {0}; for( ; cpp2::cmp_less(i,3); ++i ) {
+        auto j {0}; for( ; cpp2::cmp_less(j,3); ++j ) {
+            auto k {0}; for( ; cpp2::cmp_less(k,3); ++k ) {
+                std::cout 
+                    << i << " " 
+                    << j << " " 
+                    << k << ": " 
+                    << ([_0 = i, _1 = j, _2 = k]{ return _0==_1 && _1==_2; }()) << " " 
+                    << ([_0 = i, _1 = j, _2 = k]{ return cpp2::cmp_less(_0,_1) && cpp2::cmp_less_eq(_1,_2); }()) << " " 
+                    << ([_0 = i, _1 = j, _2 = k]{ return cpp2::cmp_greater_eq(_0,_1) && cpp2::cmp_greater(_1,_2); }()) << "\n";
+            }
+        }
+    }
+}
+

regression-tests/test-results/pure2-chained-comparisons.cpp2.output

@@ -0,0 +1,2 @@
+pure2-chained-comparisons.cpp2... ok (all Cpp2, passes safety checks)
+

regression-tests/test-results/pure2-look-up-parameter-across-unnamed-function.cpp

@@ -25,7 +25,7 @@ struct g__ret {
 [[nodiscard]] auto f() -> f__ret{
     int ri {0};
 #line 3 "pure2-look-up-parameter-across-unnamed-function.cpp2"
-    auto pred {[](auto const& e) -> bool{return e == 1; }}; 
+    auto pred {[](auto const& e) -> bool{return e==1; }}; 
     ri = 42;
     return  { std::move(ri) }; // "return;" is implicit"
 }
@@ -34,7 +34,7 @@ struct g__ret {
         cpp2::deferred_init<int> ri;
 #line 9 "pure2-look-up-parameter-across-unnamed-function.cpp2"
     ri.construct(0);
-    auto pred {[](auto const& e) -> bool{return e == 1; }}; 
+    auto pred {[](auto const& e) -> bool{return e==1; }}; 
     ri.value() = 42;
     return  { std::move(ri.value()) }; 
 }