Starting over on function types - initial support for function types in <> lists (#1183)

* Starting over on function types - initial support for function types in <> lists

Should generally support std::function<> style uses

Aside: I'm happy to find that C++ allows parameter names in function types, thank you WG21! I hadn't seen those used in examples so I had been expecting that cppfront would have to suppress those, but std::function< int ( std::string& param_name ) > is legal code. Sweet.

This commit does not yet support pointer-to-function local variables...

* Add support for pointer-to-function variables

* Add docs examples for function typeids with std::function & *pfn

* Add support for pointer to function parameter types

* Support function type ids in type aliases

Author: hsutter

Diff for: docs/cpp2/contracts.md

@@ -57,7 +57,7 @@ Contract groups are useful to enable or disable or [set custom handlers](#violat
 
 You can create new contract groups just by creating new objects that have a `.report_violation` function. The object's name is the contract group's name. The object can be at any scope: local, global, or heap.
 
-For example, here are some ways to use contract groups of type [`cpp2::contract_group`](#violation_handlers), which is a convenient group type:
+For example, here are some ways to use contract groups of type [`cpp2::contract_group`](#violation-handlers), which is a convenient group type:
 
 ``` cpp title="Using contract groups" hl_lines="1 4 6 10-12"
 group_a: cpp2::contract_group = ();          // a global group

Diff for: docs/cpp2/functions.md

@@ -12,7 +12,9 @@ func: ( /* no parameters */ ) = { /* empty body */ }
 ```
 
 
-## <a id="parameters"></a> Parameters
+## <a id="function-signatures"></a> Function signatures: Parameters, returns, and using function types
+
+### <a id="parameters"></a> Parameters
 
 The parameter list is a [list](common.md#lists) enclosed by `(` `)` parentheses. Each parameter is declared using the [same unified syntax](declarations.md) as used for all declarations. For example:
 
@@ -72,7 +74,7 @@ wrap_f: (
 ```
 
 
-## <a id="return-values"></a> Return values
+### <a id="return-values"></a> Return values
 
 A function can return either of the following. The default is `#!cpp -> void`.
 
@@ -152,7 +154,7 @@ main: () = {
 ```
 
 
-### <a id="nodiscard-outputs"></a> Function outputs are not implicitly discardable
+#### <a id="nodiscard-outputs"></a> Function outputs are not implicitly discardable
 
 A function's outputs are its return values, and the "out" state of any `out` and `inout` parameters.
 
@@ -200,9 +202,29 @@ main: ()
 > - A function call written in Cpp2 `x.f()` member call syntax always treats a non-`#!cpp void` return type as not discardable, even if the function was written in Cpp1 syntax that did not write `[[nodiscard]]`.
 
 
+### <a id = "function-types"></a> Using function types
+
+The same function parameter/return syntax can be used as a function type, for example to instantiate `std::function` or to declare a pointer to function variable. For example:
+
+``` cpp title="Using function types with std::function and *pfunc" hl_lines="4 7"
+decorate_int: (i: i32) -> std::string = "--> (i)$ <--";
+
+main: () = {
+    pf1: std::function< (i: i32) -> std::string > = decorate_int&;
+    std::cout << "pf1(123) returned \"(pf1(123))$\"\n";
+
+    pf2: * (i: i32) -> std::string = decorate_int&;
+    std::cout << "pf2(456) returned \"(pf2(456))$\"\n";
+}
+//  Prints:
+//    pf1 returned "--> 123 <--"
+//    pf2 returned "--> 456 <--"
+```
+
+
 ## <a id="control flow"></a> Control flow
 
-## <a id="branches"></a> `#!cpp if`, `#!cpp else` — Branches
+### <a id="branches"></a> `#!cpp if`, `#!cpp else` — Branches
 
 `if` and `else` are like always in C++, except that `(` `)` parentheses around the condition are not required. Instead, `{` `}` braces around a branch body *are* required. For example:
 
@@ -216,7 +238,7 @@ else {
 ```
 
 
-## <a id="loops"></a> `#!cpp for`, `#!cpp while`, `#!cpp do` — Loops
+### <a id="loops"></a> `#!cpp for`, `#!cpp while`, `#!cpp do` — Loops
 
 **`#!cpp do`** and **`#!cpp while`** are like always in C++, except that `(` `)` parentheses around the condition are not required. Instead, `{` `}` braces around the loop body *are* required.
 
@@ -296,7 +318,7 @@ Line by line:
 - `next i++`: The end-of-loop-iteration statement. Note `++` is always postfix in Cpp2.
 
 
-### Loop names, `#!cpp break`, and `#!cpp continue`
+#### Loop names, `#!cpp break`, and `#!cpp continue`
 
 Loops can be named using the usual **name `:`** syntax that introduces all names, and `#!cpp break` and `#!cpp continue` can refer to those names. For example:
 

Diff for: include/cpp2util.h

@@ -518,15 +518,17 @@ inline std::string join(List const& list) {
 //
 //  Conveniences for expressing Cpp1 references (rarely useful)
 // 
-//  Note: Only needed in rare cases to take full control of matching a
-//        Cpp1 signature exactly. Most cases don't need this, for example
-//        a Cpp1 virtual function signature declaration like
+//  Note: Only needed in rare cases to take full control of matching an
+//        odd Cpp1 signature exactly. Most cases don't need this... for
+//        example, a Cpp1 virtual function signature declaration like
 // 
-//              virtual void f(int&) const
+//              virtual void myfunc(int& val) const
 // 
 //        can already be directly overriden by a Cpp2 declaration of
 // 
-//              f: (override this, inout val : int)
+//              myfunc: (override this, inout val: int)
+//                  // identical to this in Cpp1 syntax:
+//                  //  void myfunc(int& val) const override
 // 
 //        without any need to say cpp1_ref on the int parameter.
 // 

Diff for: regression-tests/pure2-function-typeids.cpp2

@@ -0,0 +1,102 @@
+
+//  --- Scaffolding
+
+f: () = std::cout << "hello world!\n";
+
+g_in   : (      s: std::string) = std::cout << "Come in, (s)$\n";
+g_inout: (inout s: std::string) = std::cout << "Come in awhile, but take some biscuits on your way out, (s)$!\n";
+g_out  : (out   s: std::string) = s = "A Powerful Mage";
+g_move : (move  s: std::string) = std::cout << "I hear you've moving, (s)$?\n";
+
+h_forward: (inout s: std::string) -> forward std::string = { std::cout << "Inout (s)$ ... "; return s; }
+h_out    : (      s: std::string) ->         std::string = { std::cout << "In (s)$ ... "; return "yohoho"; }
+
+f1: (a: std::function< (x:int) -> int >) -> int = a(1);
+f2: (a:              * (x:int) -> int  ) -> int = a(2);
+g :                    (x:int) -> int           = x+42;
+
+
+// --- Tests for type aliases
+
+A_h_forward: type == (inout s: std::string) -> forward std::string;
+
+
+main: () = 
+{
+    //  --- Test basic/degenerate cases
+
+    //  Test std::function< void() >
+    ff: std::function< () -> void > = f&;
+    ff();
+
+    //  Ordinary pointer to function, deduced (always worked)
+    pf: * () -> void = f&;
+    pf();
+
+
+    //  --- Tests for parameters
+    //      Note: Not forward parameters which imply a template...
+    //            function type-ids are for single function signatures
+
+    fg_in   : std::function< (      s: std::string) -> void > = g_in&;
+    fg_inout: std::function< (inout s: std::string) -> void > = g_inout&;
+    fg_out  : std::function< (out   s: std::string) -> void > = g_out&;
+    fg_move : std::function< (move  s: std::string) -> void > = g_move&;
+    pg_in   :              * (      s: std::string) -> void   = g_in&;
+    pg_inout:              * (inout s: std::string) -> void   = g_inout&;
+    pg_out  :              * (out   s: std::string) -> void   = g_out&;
+    pg_move :              * (move  s: std::string) -> void   = g_move&;
+
+    frodo: std::string = "Frodo";
+    sam  : std::string = "Sam";
+
+    //  Test in param
+    fg_in(frodo);
+    pg_in(sam);
+
+    //  Test inout
+    fg_inout(frodo);
+    pg_inout(sam);
+
+    //  Test out
+    gandalf  : std::string;
+    galadriel: std::string;
+    fg_out(out gandalf);
+    std::cout << "fg_out initialized gandalf to: (gandalf)$\n";
+    pg_out(out galadriel);
+    std::cout << "pg_out initialized galadriel to: (galadriel)$\n";
+    gandalf   = "Gandalf";
+    galadriel = "Galadriel";
+
+    //  Test move
+    fg_move(frodo); // last use, so (move frodo) is not required
+    pg_move(sam);   // last use, so (move sam) is not required
+
+
+    //  --- Tests for single anonymous returns
+    //      Note: Not multiple named return values... function-type-ids 
+    //      are for Cpp1-style (single anonymous, possibly void) returns
+
+    fh_forward: std::function< (inout s: std::string) -> forward std::string > = h_forward&;
+    fh_out    : std::function< (      s: std::string) ->         std::string > = h_out&;
+    ph_forward:              * (inout s: std::string) -> forward std::string   = h_forward&;
+    ph_out    :              * (      s: std::string) ->         std::string   = h_out&;
+
+    ph_forward2: * A_h_forward = h_forward&;
+
+    //  Test forward return
+    std::cout << "fh_forward returned: (fh_forward(gandalf))$\n";
+    std::cout << "ph_forward returned: (ph_forward(galadriel))$\n";
+    std::cout << "ph_forward2 returned: (ph_forward2(galadriel))$\n";
+
+    //  Test out return
+    std::cout << "fh_out returned: (fh_out(gandalf))$\n";
+    std::cout << "ph_out returned: (ph_out(galadriel))$\n";
+
+
+    //  --- Tests for function parameters
+    std::cout << "(f1(g&))$\n";
+    std::cout << "(f2(g&))$\n";
+
+
+}

Diff for: regression-tests/test-results/clang-12-c++20/pure2-function-typeids.cpp.execution

@@ -0,0 +1,17 @@
+hello world!
+hello world!
+Come in, Frodo
+Come in, Sam
+Come in awhile, but take some biscuits on your way out, Frodo!
+Come in awhile, but take some biscuits on your way out, Sam!
+fg_out initialized gandalf to: A Powerful Mage
+pg_out initialized galadriel to: A Powerful Mage
+I hear you've moving, Frodo?
+I hear you've moving, Sam?
+Inout Gandalf ... fh_forward returned: Gandalf
+Inout Galadriel ... ph_forward returned: Galadriel
+Inout Galadriel ... ph_forward2 returned: Galadriel
+In Gandalf ... fh_out returned: yohoho
+In Galadriel ... ph_out returned: yohoho
+43
+44

Diff for: regression-tests/test-results/clang-12-c++20/run-tests-clang-12.sh

@@ -20,5 +20,6 @@ do
     fi
 done
 rm -f *.obj *.exp *.lib
+find . -type f -exec bash -c "[ ! -s \"{}\" ] && rm \"{}\"" \;
 printf "\nDone: %s .cpp tests compiled\n" "$count"
 printf "\n      %s .cpp executables generated and run\n" "$exe_count"

Diff for: regression-tests/test-results/gcc-10-c++20/pure2-function-typeids.cpp.execution

@@ -0,0 +1,17 @@
+hello world!
+hello world!
+Come in, Frodo
+Come in, Sam
+Come in awhile, but take some biscuits on your way out, Frodo!
+Come in awhile, but take some biscuits on your way out, Sam!
+fg_out initialized gandalf to: A Powerful Mage
+pg_out initialized galadriel to: A Powerful Mage
+I hear you've moving, Frodo?
+I hear you've moving, Sam?
+Inout Gandalf ... fh_forward returned: Gandalf
+Inout Galadriel ... ph_forward returned: Galadriel
+Inout Galadriel ... ph_forward2 returned: Galadriel
+In Gandalf ... fh_out returned: yohoho
+In Galadriel ... ph_out returned: yohoho
+43
+44

Diff for: regression-tests/test-results/gcc-10-c++20/run-tests-gcc-10.sh

@@ -20,5 +20,6 @@ do
     fi
 done
 rm -f *.obj *.exp *.lib
+find . -type f -exec bash -c "[ ! -s \"{}\" ] && rm \"{}\"" \;
 printf "\nDone: %s .cpp tests compiled\n" "$count"
 printf "\n      %s .cpp executables generated and run\n" "$exe_count"

Diff for: regression-tests/test-results/gcc-14-c++2b/mixed-bugfix-for-ufcs-non-local.cpp.output

@@ -1,41 +1,41 @@
 In file included from mixed-bugfix-for-ufcs-non-local.cpp:6:
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 | class finally_success
+ 2100 | 
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     finally(finally&& that) noexcept
+ 2137 |     ~finally() noexcept { f(); }
       |                                                           ^         
 mixed-bugfix-for-ufcs-non-local.cpp2:13:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:13:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 | class finally_success
+ 2100 | 
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     finally(finally&& that) noexcept
+ 2137 |     ~finally() noexcept { f(); }
       |                                                           ^         
 mixed-bugfix-for-ufcs-non-local.cpp2:21:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:21:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 | class finally_success
+ 2100 | 
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     finally(finally&& that) noexcept
+ 2137 |     ~finally() noexcept { f(); }
       |                                                           ^         
 mixed-bugfix-for-ufcs-non-local.cpp2:31:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:31:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 | class finally_success
+ 2100 | 
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     finally(finally&& that) noexcept
+ 2137 |     ~finally() noexcept { f(); }
       |                                                           ^         
 mixed-bugfix-for-ufcs-non-local.cpp2:33:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:33:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 | class finally_success
+ 2100 | 
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     finally(finally&& that) noexcept
+ 2137 |     ~finally() noexcept { f(); }
       |                                                           ^         
 mixed-bugfix-for-ufcs-non-local.cpp2:21:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:21:36: error: template argument 1 is invalid

Diff for: regression-tests/test-results/gcc-14-c++2b/pure2-function-typeids.cpp.execution

@@ -0,0 +1,17 @@
+hello world!
+hello world!
+Come in, Frodo
+Come in, Sam
+Come in awhile, but take some biscuits on your way out, Frodo!
+Come in awhile, but take some biscuits on your way out, Sam!
+fg_out initialized gandalf to: A Powerful Mage
+pg_out initialized galadriel to: A Powerful Mage
+I hear you've moving, Frodo?
+I hear you've moving, Sam?
+Inout Gandalf ... fh_forward returned: Gandalf
+Inout Galadriel ... ph_forward returned: Galadriel
+Inout Galadriel ... ph_forward2 returned: Galadriel
+In Gandalf ... fh_out returned: yohoho
+In Galadriel ... ph_out returned: yohoho
+43
+44

Diff for: regression-tests/test-results/gcc-14-c++2b/run-tests-gcc-14.sh

@@ -20,5 +20,6 @@ do
     fi
 done
 rm -f *.obj *.exp *.lib
+find . -type f -exec bash -c "[ ! -s \"{}\" ] && rm \"{}\"" \;
 printf "\nDone: %s .cpp tests compiled\n" "$count"
 printf "\n      %s .cpp executables generated and run\n" "$exe_count"

Diff for: regression-tests/test-results/msvc-2022-c++latest/pure2-function-typeids.cpp.execution

@@ -0,0 +1,17 @@
+hello world!
+hello world!
+Come in, Frodo
+Come in, Sam
+Come in awhile, but take some biscuits on your way out, Frodo!
+Come in awhile, but take some biscuits on your way out, Sam!
+fg_out initialized gandalf to: A Powerful Mage
+pg_out initialized galadriel to: A Powerful Mage
+I hear you've moving, Frodo?
+I hear you've moving, Sam?
+Inout Gandalf ... fh_forward returned: Gandalf
+Inout Galadriel ... ph_forward returned: Galadriel
+Inout Galadriel ... ph_forward2 returned: Galadriel
+In Gandalf ... fh_out returned: yohoho
+In Galadriel ... ph_out returned: yohoho
+43
+44

Diff for: regression-tests/test-results/msvc-2022-c++latest/pure2-function-typeids.cpp.output

@@ -0,0 +1 @@
+pure2-function-typeids.cpp

Diff for: regression-tests/test-results/msvc-2022-c++latest/run-tests-msvc-2022.bat

@@ -26,6 +26,7 @@ for %%f in (*.cpp) do (
     )
 )
 del pure2-*.obj mixed-*.obj *.exp *.lib
+..\..\rm-empty-files.bat
 echo.
 echo Done: %count% .cpp tests compiled
 echo.