Make output -Wunused-parameter-clean, and add real support for _ unnamed parameters, closes #560

Emit `[[maybe_unused]]` on a `that` parameter if the class is empty.
Add -Wunused-parameter to my GCC and Clang regression tests.
Add `_` unnamed parameter support, and use ordinals instead of line/col numbers to keep the generated names stable.

As an example from one of the updated regression tests that had a helper function to just accept (but not use) five generic parameters, that function is now just: `call: (_, _, _, _, _) = { }`

Author: hsutter

regression-tests/mixed-forwarding.cpp2

@@ -8,9 +8,9 @@ struct X {
     X(X &&     that) : i{that.i} { std::cout << "move X " << i << "\n"; }
 };
 
-copy_from: (copy x:_) = { }
+copy_from: (copy _) = { }
 
-use: (x:_) = {}
+use: (_) = {}
 
 // invoking each of these with an rvalue std::pair argument ...
 apply_implicit_forward: (forward t: std::pair<X, X>) = {

regression-tests/mixed-parameter-passing-with-forward.cpp2

@@ -3,12 +3,12 @@
 #include <cstdlib>
 #include <ctime>
 
-copy_from: (copy x:_) = { }
+copy_from: (copy _) = { }
 
 parameter_styles: (
-    in      a: std::string, // "in" is default
+    in      _: std::string, // "in" is default
     copy    b: std::string,
-    inout   c: std::string,
+    inout   _: std::string,
     move    d: std::string,
     forward e: std::string
     )

regression-tests/mixed-parameter-passing.cpp2

@@ -3,12 +3,12 @@
 #include <cstdlib>
 #include <ctime>
 
-copy_from: (copy x:_) = { }
+copy_from: (copy _) = { }
 
 parameter_styles: (
-    in    a: std::string, // "in" is default
+    in    _: std::string, // "in" is default
     copy  b: std::string,
-    inout c: std::string,
+    inout _: std::string,
     move  d: std::string
     )
 = {

regression-tests/mixed-postfix-expression-custom-formatting.cpp2

@@ -1,5 +1,5 @@
 
-call: (v:_, w:_, x:_, y:_, z:_) = { }
+call: (_, _, _, _, _) = { }
 
 test: (a:_) -> std::string = {
     return call( a,

regression-tests/pure2-bugfix-for-discard-precedence.cpp2

@@ -1,8 +1,8 @@
 quantity: type = {
   number: i32;
-  operator=: (out this, _: std::in_place_t, x: i32) = {
+  operator=: (out this, i: std::in_place_t, x: i32) = {
     number = x;
-    _      = _;
+    _      = i;
   }
   operator+=: (inout this, that) -> forward quantity = {
     number += that.number;

regression-tests/pure2-bugfix-for-memberwise-base-assignment.cpp2

@@ -1,7 +1,7 @@
 Base: type = {
   operator=: (out this) = { }
   operator=: (out this, that)       = std::cout << "(out this, that)\n";
-  operator=: (implicit out this, x) = std::cout << "(implicit out this, x)\n";
+  operator=: (implicit out this, _) = std::cout << "(implicit out this, _)\n";
 }
 
 Derived: type = {

regression-tests/pure2-types-basics.cpp2

@@ -19,7 +19,7 @@ myclass : type = {
 
     operator=: (out this, x: int, s: std::string) = {
         this.data = 77;
-        this.more = s + " plugh";
+        this.more = s + std::to_string(x) + " plugh";
         std::cout << "myclass: from int and string\n";
         print();
     }

regression-tests/pure2-types-inheritance.cpp2

@@ -5,7 +5,7 @@ Human: @interface type = {
 
 N: namespace = {
     Machine: @polymorphic_base <I:int> type = {
-        operator=: (out this, id: std::string) = {}
+        operator=: (out this, _: std::string) = {}
         work:      (virtual this);
     }
 }

regression-tests/pure2-ufcs-member-access-and-chaining.cpp2

@@ -21,7 +21,7 @@ main: () -> int = {
     42.no_return();
 }
 
-no_return: (x: int) = { }
+no_return: (_) = { }
 
 ufcs: (i:int) -> int = {
     return i+2;
@@ -37,5 +37,5 @@ get_i: (r:_) -> int = {
 }
 
 //  And a test for non-local UFCS, which shouldn't do a [&] capture
-f: (x)->int = 0;
+f: (_)->int = 0;
 y: int = 0.f();

regression-tests/test-results/clang-12/pure2-types-basics.cpp.execution

@@ -11,7 +11,7 @@ myclass: explicit from string
 myclass: default
     data: 504, more: 3.141590
 myclass: from int and string
-    data: 77, more: hair plugh
+    data: 77, more: hair1 plugh
 x's state before assignments:     data: 1, more: 504
 myclass: implicit from int
     data: 84, more: 504

regression-tests/test-results/clang-12/run-tests-clang-12.sh

@@ -10,7 +10,7 @@ for f in *.cpp
 do
     let count=count+1
     printf "[%s] Starting clang++-12 %s\n" "$count" "$f"
-    clang++-12 -I../../../include -std=c++20 -pthread -o test.exe $f > $f.output 2>&1
+    clang++-12 -I../../../include -std=c++20 -pthread -Wunused-parameter -o test.exe $f > $f.output 2>&1
     rm -f $f
     if test -f "test.exe"; then
         let exe_count=exe_count+1

regression-tests/test-results/gcc-13/pure2-types-basics.cpp.execution

@@ -11,7 +11,7 @@ myclass: explicit from string
 myclass: default
     data: 504, more: 3.141590
 myclass: from int and string
-    data: 77, more: hair plugh
+    data: 77, more: hair1 plugh
 x's state before assignments:     data: 1, more: 504
 myclass: implicit from int
     data: 84, more: 504

regression-tests/test-results/gcc-13/run-tests-gcc-13.sh

@@ -10,7 +10,7 @@ for f in *.cpp
 do
     let count=count+1
     printf "[%s] Starting gcc 13 %s\n" "$count" "$f"
-    g++ -I../../../include -std=c++20 -pthread -o test.exe $f > $f.output 2>&1
+    g++ -I../../../include -std=c++20 -pthread -Wunused-parameter -o test.exe $f > $f.output 2>&1
     rm -f $f
     if test -f "test.exe"; then
         let exe_count=exe_count+1

regression-tests/test-results/mixed-forwarding.cpp

@@ -20,9 +20,9 @@ struct X {
 };
 
 #line 11 "mixed-forwarding.cpp2"
-auto copy_from(auto x) -> void;
+auto copy_from([[maybe_unused]] auto param1) -> void;
 
-auto use(auto const& x) -> void;
+auto use([[maybe_unused]] auto const& param1) -> void;
 
 // invoking each of these with an rvalue std::pair argument ...
 auto apply_implicit_forward(auto&& t) -> void
@@ -46,9 +46,9 @@ CPP2_REQUIRES (std::is_same_v<CPP2_TYPEOF(t), std::pair<X,X>>)
 
 
 #line 11 "mixed-forwarding.cpp2"
-auto copy_from(auto x) -> void{}
+auto copy_from([[maybe_unused]] auto param1) -> void{}
 
-auto use(auto const& x) -> void{}
+auto use([[maybe_unused]] auto const& param1) -> void{}
 
 #line 16 "mixed-forwarding.cpp2"
 auto apply_implicit_forward(auto&& t) -> void

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

@@ -15,12 +15,12 @@
 #include <ctime>
 
 #line 6 "mixed-parameter-passing-with-forward.cpp2"
-auto copy_from(auto x) -> void;
+auto copy_from([[maybe_unused]] auto param1) -> void;
 
 auto parameter_styles(
-    cpp2::in<std::string> a, // "in" is default
+    [[maybe_unused]] cpp2::in<std::string> param1, // "in" is default
     std::string b, 
-    std::string& c, 
+    [[maybe_unused]] std::string& param3, 
     std::string&& d, 
     auto&& e
     ) -> void
@@ -36,12 +36,12 @@ CPP2_REQUIRES (std::is_same_v<CPP2_TYPEOF(e), std::string>)
 
 
 #line 6 "mixed-parameter-passing-with-forward.cpp2"
-auto copy_from(auto x) -> void{}
+auto copy_from([[maybe_unused]] auto param1) -> void{}
 
 auto parameter_styles(
-    cpp2::in<std::string> a, 
+    [[maybe_unused]] cpp2::in<std::string> param1, 
     std::string b, 
-    std::string& c, 
+    [[maybe_unused]] std::string& param3, 
     std::string&& d, 
     auto&& e
     ) -> void

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

@@ -15,12 +15,12 @@
 #include <ctime>
 
 #line 6 "mixed-parameter-passing.cpp2"
-auto copy_from(auto x) -> void;
+auto copy_from([[maybe_unused]] auto param1) -> void;
 
 auto parameter_styles(
-    cpp2::in<std::string> a, // "in" is default
+    [[maybe_unused]] cpp2::in<std::string> param1, // "in" is default
     std::string b, 
-    std::string& c, 
+    [[maybe_unused]] std::string& param3, 
     std::string&& d
     ) -> void;
 
@@ -32,12 +32,12 @@ auto parameter_styles(
 
 
 #line 6 "mixed-parameter-passing.cpp2"
-auto copy_from(auto x) -> void{}
+auto copy_from([[maybe_unused]] auto param1) -> void{}
 
 auto parameter_styles(
-    cpp2::in<std::string> a, 
+    [[maybe_unused]] cpp2::in<std::string> param1, 
     std::string b, 
-    std::string& c, 
+    [[maybe_unused]] std::string& param3, 
     std::string&& d
     ) -> void
 {

regression-tests/test-results/mixed-postfix-expression-custom-formatting.cpp

@@ -11,7 +11,7 @@
 
 
 #line 2 "mixed-postfix-expression-custom-formatting.cpp2"
-auto call(auto const& v, auto const& w, auto const& x, auto const& y, auto const& z) -> void;
+auto call([[maybe_unused]] auto const& param1, [[maybe_unused]] auto const& param2, [[maybe_unused]] auto const& param3, [[maybe_unused]] auto const& param4, [[maybe_unused]] auto const& param5) -> void;
 
 [[nodiscard]] auto test(auto const& a) -> std::string;
 
@@ -24,7 +24,7 @@ auto call(auto const& v, auto const& w, auto const& x, auto const& y, auto const
 
 
 #line 2 "mixed-postfix-expression-custom-formatting.cpp2"
-auto call(auto const& v, auto const& w, auto const& x, auto const& y, auto const& z) -> void{}
+auto call([[maybe_unused]] auto const& param1, [[maybe_unused]] auto const& param2, [[maybe_unused]] auto const& param3, [[maybe_unused]] auto const& param4, [[maybe_unused]] auto const& param5) -> void{}
 
 [[nodiscard]] auto test(auto const& a) -> std::string{
     return call(a, 

regression-tests/test-results/msvc-2022/pure2-types-basics.cpp.execution

@@ -11,7 +11,7 @@ myclass: explicit from string
 myclass: default
     data: 504, more: 3.141590
 myclass: from int and string
-    data: 77, more: hair plugh
+    data: 77, more: hair1 plugh
 x's state before assignments:     data: 1, more: 504
 myclass: implicit from int
     data: 84, more: 504

regression-tests/test-results/pure2-bugfix-for-discard-precedence.cpp

@@ -15,7 +15,7 @@ class quantity;
 #line 1 "pure2-bugfix-for-discard-precedence.cpp2"
 class quantity {
   private: cpp2::i32 number; 
-  public: explicit quantity(cpp2::in<std::in_place_t> _, cpp2::in<cpp2::i32> x);
+  public: explicit quantity(cpp2::in<std::in_place_t> i, cpp2::in<cpp2::i32> x);
 
 
 #line 7 "pure2-bugfix-for-discard-precedence.cpp2"
@@ -35,12 +35,12 @@ auto main() -> int;
 
 
 #line 3 "pure2-bugfix-for-discard-precedence.cpp2"
-  quantity::quantity(cpp2::in<std::in_place_t> _, cpp2::in<cpp2::i32> x)
+  quantity::quantity(cpp2::in<std::in_place_t> i, cpp2::in<cpp2::i32> x)
     : number{ x }
 #line 3 "pure2-bugfix-for-discard-precedence.cpp2"
   {
 
-    static_cast<void>(_);
+    static_cast<void>(i);
   }
   auto quantity::operator+=(quantity const& that) -> quantity&{
     number += that.number;

regression-tests/test-results/pure2-bugfix-for-memberwise-base-assignment.cpp

@@ -19,19 +19,19 @@ class Derived;
 #line 1 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
 class Base {
   public: explicit Base();
-  public: Base(Base const& that);
+  public: Base([[maybe_unused]] Base const& that);
 
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  public: auto operator=(Base const& that) -> Base& ;
+  public: auto operator=([[maybe_unused]] Base const& that) -> Base& ;
 
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  public: Base(Base&& that) noexcept;
+  public: Base([[maybe_unused]] Base&& that) noexcept;
 
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  public: auto operator=(Base&& that) noexcept -> Base& ;
-  public: Base(auto const& x);
+  public: auto operator=([[maybe_unused]] Base&& that) noexcept -> Base& ;
+  public: Base([[maybe_unused]] auto const& param2);
 #line 4 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  public: auto operator=(auto const& x) -> Base& ;
+  public: auto operator=([[maybe_unused]] auto const& param2) -> Base& ;
 };
 
 class Derived: public Base {
@@ -49,22 +49,22 @@ auto main() -> int;
 
 #line 2 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
   Base::Base(){}
-  Base::Base (Base const& that) { std::cout << "(out this, that)\n"; }
+  Base::Base ([[maybe_unused]] Base const& that) { std::cout << "(out this, that)\n"; }
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  auto Base::operator=(Base const& that) -> Base&  { std::cout << "(out this, that)\n";
+  auto Base::operator=([[maybe_unused]] Base const& that) -> Base&  { std::cout << "(out this, that)\n";
                                       return *this;
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
                                      }
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  Base::Base (Base&& that) noexcept { std::cout << "(out this, that)\n"; }
+  Base::Base ([[maybe_unused]] Base&& that) noexcept { std::cout << "(out this, that)\n"; }
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  auto Base::operator=(Base&& that) noexcept -> Base&  { std::cout << "(out this, that)\n";
+  auto Base::operator=([[maybe_unused]] Base&& that) noexcept -> Base&  { std::cout << "(out this, that)\n";
                                       return *this;
 #line 3 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
                                      }
-  Base::Base(auto const& x) { std::cout << "(implicit out this, x)\n";  }
+  Base::Base([[maybe_unused]] auto const& param2) { std::cout << "(implicit out this, _)\n";  }
 #line 4 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
-  auto Base::operator=(auto const& x) -> Base&  { std::cout << "(implicit out this, x)\n";
+  auto Base::operator=([[maybe_unused]] auto const& param2) -> Base&  { std::cout << "(implicit out this, _)\n";
                                       return *this;
 #line 4 "pure2-bugfix-for-memberwise-base-assignment.cpp2"
    }

regression-tests/test-results/pure2-types-basics.cpp

@@ -138,7 +138,7 @@ namespace N {
 
     myclass::myclass(cpp2::in<int> x, cpp2::in<std::string> s)
         : data{ 77 }
-        , more{ s + " plugh" }
+        , more{ s + std::to_string(x) + " plugh" }
 #line 20 "pure2-types-basics.cpp2"
     {
 

regression-tests/test-results/pure2-types-inheritance.cpp

@@ -39,7 +39,7 @@ public: virtual ~Human() noexcept;
 
 namespace N {
     template<int I> class Machine {
-        public: explicit Machine(cpp2::in<std::string> id);
+        public: explicit Machine([[maybe_unused]] cpp2::in<std::string> param2);
         public: virtual auto work() const -> void = 0;
 
     public: virtual ~Machine() noexcept;
@@ -97,7 +97,7 @@ auto main() -> int;
 #line 6 "pure2-types-inheritance.cpp2"
 namespace N {
 
-        template <int I> Machine<I>::Machine(cpp2::in<std::string> id){}
+        template <int I> Machine<I>::Machine([[maybe_unused]] cpp2::in<std::string> param2){}
 
         template <int I> Machine<I>::~Machine() noexcept{}
 

regression-tests/test-results/pure2-ufcs-member-access-and-chaining.cpp

@@ -15,7 +15,7 @@
 
 
 #line 24 "pure2-ufcs-member-access-and-chaining.cpp2"
-auto no_return(cpp2::in<int> x) -> void;
+auto no_return([[maybe_unused]] auto const& param1) -> void;
 
 [[nodiscard]] auto ufcs(cpp2::in<int> i) -> int;
     struct fun__ret { int i; };
@@ -32,7 +32,7 @@ auto no_return(cpp2::in<int> x) -> void;
 
 #line 39 "pure2-ufcs-member-access-and-chaining.cpp2"
 //  And a test for non-local UFCS, which shouldn't do a [&] capture
-[[nodiscard]] auto f(auto const& x) -> int;
+[[nodiscard]] auto f([[maybe_unused]] auto const& param1) -> int;
 extern int y;
 
 //=== Cpp2 function definitions =================================================
@@ -61,7 +61,7 @@ extern int y;
     CPP2_UFCS_0(no_return, 42);
 }
 
-auto no_return(cpp2::in<int> x) -> void{}
+auto no_return([[maybe_unused]] auto const& param1) -> void{}
 
 [[nodiscard]] auto ufcs(cpp2::in<int> i) -> int{
     return i + 2; 
@@ -79,6 +79,6 @@ auto no_return(cpp2::in<int> x) -> void{}
 }
 
 #line 40 "pure2-ufcs-member-access-and-chaining.cpp2"
-[[nodiscard]] auto f(auto const& x) -> int { return 0;  }
+[[nodiscard]] auto f([[maybe_unused]] auto const& param1) -> int { return 0;  }
 int y {CPP2_UFCS_0_NONLOCAL(f, 0)};