Allow void if expressions (#1164)

Enhancements:
- Allow void values in if expressions (closes #1159)
- Pass type constraints through if let and nested if (closes #1160)

Bugs fixed:
- Signature help not available for constructor calls without new (closes #1161)
- let in not accepted in return statement (closes #1162)
- Lambdas cannot infer void return type (closes #1163)

.config/dotnet-tools.json

@@ -15,7 +15,7 @@
       ]
     },
     "ghul.compiler": {
-      "version": "0.8.36",
+      "version": "0.8.37",
       "commands": [
         "ghul-compiler"
       ]

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <Version>0.8.37-alpha.131</Version>
+    <Version>0.8.38-alpha.30</Version>
     <NoWarn>$(NoWarn);NU1507</NoWarn>
   </PropertyGroup>
   <ItemGroup>

integration-tests/execution/implied-anonymous-function-argument-types-2/test.ghul

@@ -1,23 +1,21 @@
-namespace Test is
-    use Std = IO.Std;
+use Std = IO.Std;
 
-    class Main is
-        entry() static is
-
-
-            Main().test();
-        si
-
-        init() is
-        si
+class Main is
+    entry() static is
 
-
-        test() is
-            Std.write_line("map 123 to string: " + map_int_to_string(123, i => "'" + i + "'"));
 
-            return;
-        si
+        Main().test();
+    si
 
-        map_int_to_string(i: int, f: int -> string) -> string static => f(i);
+    init() is
     si
-si
+
+
+    test() is
+        Std.write_line("map 123 to string: " + map_int_to_string(123, i => "'" + i + "'"));
+
+        return;
+    si
+
+    map_int_to_string(i: int, f: int -> string) -> string static => f(i);
+si

src/ir/values/block.ghul

@@ -2,8 +2,6 @@ namespace IR.Values is
     use TypeTyped = Semantic.Types.Typed;
     use Semantic.Types.Type;
 
-    use Logging;
-
     class BLOCK: Value, TypeTyped is
         _values: Collections.MutableList[Value];
 
@@ -14,6 +12,8 @@ namespace IR.Values is
         is_closed: bool;
         is_emitted: bool;
 
+        is_consumable: bool => true;
+
         init(type: Type) is
             super.init();
 

src/syntax/parsers/statements/node.ghul

@@ -63,6 +63,7 @@ namespace Syntax.Parsers.Statements is
                 Lexical.TOKEN.SUPER,
                 Lexical.TOKEN.REC,
                 Lexical.TOKEN.IF,
+                Lexical.TOKEN.LET,
                 Lexical.TOKEN.OPERATOR
             ];
 

src/syntax/process/compile_expressions.ghul

@@ -646,8 +646,7 @@ namespace Syntax.Process is
 
             if 
                 !function.return_type? \/ 
-                function.return_type.is_any \/ 
-                function.return_type =~ _innate_symbol_lookup.get_void_type()
+                function.return_type.is_any
             then
                 return false;
             fi
@@ -682,7 +681,7 @@ namespace Syntax.Process is
             let void_type = _innate_symbol_lookup.get_void_type();
 
             if function.return_type.is_inferred then
-                if Value.check_is_consumable(_logger, expression.expression.location, expression.expression.value) then
+                if Value.check_is_consumable_allow_void(_logger, expression.expression.location, expression.expression.value) then
                     function.set_return_type(expression.expression.value.type);
                 elif expression.expression.value? /\ expression.expression.value.type? /\ expression.expression.value.type.is_error then
                     function.set_return_type(Semantic.Types.ERROR());
@@ -711,34 +710,26 @@ namespace Syntax.Process is
         pre(function: Trees.Expressions.FUNCTION) -> bool is
             super.pre(function);
 
-            if !function.value? then
-                function.value = IR.Values.WRAPPER();
-            fi
-
-            let closure = cast Semantic.Symbols.Closure(scope_for(function));
-
-            if !closure? then
-                return true;                
-            fi
-
-            closure.map_type_arguments();
-
             return true;
         si
 
-
         visit(function: Trees.Expressions.FUNCTION) is
             try
                 _visit(function);
             catch ex: Exception
-                debug_always("{function.location} caught {ex}");
-                _logger.poison(function.location, "oops: {ex.message}");
+                _logger.exception(function.location, ex, "exception walking lambda");
             yrt            
         si
 
         _visit(function: Trees.Expressions.FUNCTION) is
+            if !function.value? then
+                function.value = IR.Values.WRAPPER();
+            fi
+
             let closure = cast Semantic.Symbols.Closure(scope_for(function));
 
+            closure.map_type_arguments();
+
             let implied_type: Type;
             let implied_argument_types: Collections.List[Type];
 
@@ -805,9 +796,6 @@ namespace Syntax.Process is
                 else
                     return_type = Semantic.Types.INFERED_RETURN_TYPE();
                 fi                
-
-                // FIXME is this needed? it's not referenced after this point
-                argument_types.add(return_type);
 
                 closure.argument_names = argument_names;
 
@@ -1297,7 +1285,7 @@ namespace Syntax.Process is
                 );
         si
 
-        resolve_constructor(location: LOCATION, right_location: LOCATION, type: Semantic.Types.Type, argument_expressions: Trees.Expressions.LIST) -> Value is
+        resolve_constructor(location: LOCATION, right_location: LOCATION, type: Semantic.Types.Type, argument_expressions: Trees.Expressions.LIST) -> (Value, Value) is
             let result: Value;
 
             let named_type = cast Semantic.Types.NAMED(type);
@@ -1328,23 +1316,15 @@ namespace Syntax.Process is
             od
 
             if !function_group? then
-                _logger.error(location, "no constructor found init({argument_types|})");                
+                _logger.error(location, "no constructor found init({argument_types|})");
 
-                return
-                    DUMMY(
-                        type,
-                        location
-                    );
+                return (cast Value(DUMMY(type, location)), cast Value(DUMMY(type, location)));
             fi
 
-            let overload_result = _overload_resolver.resolve(location, function_group, argument_types, false, true);
+            let overload_result = _overload_resolver.resolve(location, function_group, argument_types, true, true);
 
             if overload_result == null then
-                return
-                    DUMMY(
-                        type,
-                        location
-                    );
+                return (cast Value(Load.SYMBOL(null, function_group)), cast Value(DUMMY(type, location)));
             fi
 
             let function = overload_result.function;
@@ -1364,12 +1344,7 @@ namespace Syntax.Process is
             _symbol_use_locations.add_symbol_use(right_location, function);
             _symbol_use_locations.add_symbol_use(right_location, type_symbol.root_unspecialized_symbol);
 
-            return
-                NEW(
-                    type,
-                    function,
-                    arguments
-                );
+            return (cast Value(Load.SYMBOL(null, function_group)), cast Value(NEW(type, function, arguments)));
         si
 
         visit(unary: Trees.Expressions.UNARY) is
@@ -2546,7 +2521,7 @@ namespace Syntax.Process is
             fi
 
             if call.function.value.is_type_expression then
-                call.value = resolve_constructor(call.location, call.right_location, call.function.value.type, call.arguments);
+                (call.function.value, call.value) = resolve_constructor(call.location, call.right_location, call.function.value.type, call.arguments);
 
                 return;
             fi
@@ -2685,7 +2660,7 @@ namespace Syntax.Process is
                 fi
             else
                 if load_symbol? /\ load_symbol.is_type then
-                    call.value = resolve_constructor(call.location, call.right_location, load_symbol.type, call.arguments);
+                    (call.function.value, call.value) = resolve_constructor(call.location, call.right_location, load_symbol.type, call.arguments);
                 else
                     _logger.error(call.function.location, "cannot call value of non-function type {call.function.value.type}");
                     call.value = DUMMY(Semantic.Types.ERROR(), call.location);
@@ -2960,7 +2935,10 @@ namespace Syntax.Process is
                 return;
             fi
 
-            if !`if.branches | .any(b => b? /\ !b.condition?) then
+            if 
+                !`if.branches | .any(b => b? /\ !b.condition?) /\
+                (!`if.constraint? \/ !`if.constraint.is_void)
+            then
                 // if the if has no else branch, then don't bother reporting any
                 // semantic errors:
                 _logger.error(`if.location, "expected else in if expression");
@@ -2985,12 +2963,18 @@ namespace Syntax.Process is
                     continue;
                 fi
 
-                if !branch.value.check_is_consumable(_logger, branch.location) then
-                    continue;
+                if `if.constraint? then
+                    if !branch.value.check_is_consumable_allow_void(_logger, branch.location) then
+                        continue;
+                    fi
+                else
+                    if !branch.value.check_is_consumable(_logger, branch.location) then
+                        continue;
+                    fi
                 fi
 
-                if `if.constraint? then                
-                    if !`if.constraint.is_assignable_from(branch.value.type) then
+                if `if.constraint? then
+                    if !`if.constraint.is_void /\ !`if.constraint.is_assignable_from(branch.value.type) then
                         _logger.error(branch.location, string.format(`if.constraint_error_message, branch.value.type, type));
                     fi
                     seen_non_null_values = true;

src/syntax/process/generate_il.ghul

@@ -1063,6 +1063,10 @@ namespace Syntax.Process is
 
                 if `if.want_value /\ b.body.value? then
                     add(b.body.value);
+
+                    if `if.constraint? /\ `if.constraint.is_void /\ !b.body.value.type.is_void then
+                        add("pop");
+                    fi
                 fi
 
                 brancher.branch(end);

src/syntax/process/signature_help.ghul

@@ -41,10 +41,10 @@ namespace Syntax.Process is
                 return;
             fi
 
-            if !(_results?) then
-                if
-                    !call.location.contains(_target_line, _target_column) \/
-                    call.function.location.contains(_target_line, _target_column)
+            if !_results? then
+                if !call.arguments.location.contains(_target_line, _target_column) /\
+                    (!call.location.contains(_target_line, _target_column) \/
+                    call.function.location.contains(_target_line, _target_column))
                 then
                     return;
                 fi
@@ -133,7 +133,15 @@ namespace Syntax.Process is
                 return null;
             fi
 
-            if call.function.value == null then
+            let load = cast IR.Values.Load.SYMBOL(call.function.value);
+
+            if !load? then
+                return null;
+            fi
+
+            let function_group = cast Semantic.Symbols.FUNCTION_GROUP(load.symbol);
+
+            if !function_group? then
                 return null;
             fi
 
@@ -147,20 +155,13 @@ namespace Syntax.Process is
                 fi
             od
 
-            if isa IR.Values.Load.SYMBOL(call.function.value) then
-                let load = cast IR.Values.Load.SYMBOL(call.function.value);
-
-                if load.symbol? /\ isa Semantic.Symbols.FUNCTION_GROUP(load.symbol) then
-                    let function_group = cast Semantic.Symbols.FUNCTION_GROUP(load.symbol);
-                    let overload_results = _overload_resolver.find_matches(function_group, argument_types);
-
-                    if overload_results.results.count == 0 then
-                        return null;
-                    fi
+            let overload_results = _overload_resolver.find_matches(function_group, argument_types);
 
-                    return overload_results;
-                fi
+            if overload_results.results.count == 0 then
+                return null;
             fi
+
+            return overload_results;
         si
 
         help_for(`new: Trees.Expressions.NEW) -> Semantic.OVERLOAD_MATCHES_RESULT is

src/syntax/trees/expressions/let_in.ghul

@@ -1,6 +1,6 @@
 namespace Syntax.Trees.Expressions is
     use Source;
-    
+
     class LET_IN: Expression is
         variables: Variables.LIST;
         expression: Expression;
@@ -26,6 +26,12 @@ namespace Syntax.Trees.Expressions is
             fi
         si
 
+        try_set_constraint(constraint: Semantic.Types.Type, error_message: string) is
+            if expression? then
+                expression.try_set_constraint(constraint, error_message);
+            fi
+        si
+
         accept(visitor: Visitor) is
             visitor.visit(self);
         si

src/syntax/trees/statements/if.ghul

@@ -16,6 +16,10 @@ namespace Syntax.Trees.Statements is
         try_set_constraint(constraint: Semantic.Types.Type, error_message: string) is
             self.constraint = constraint;
             self.constraint_error_message = error_message;
+
+            for b in branches do
+                b.body.try_set_constraint(constraint, error_message);
+            od
         si
 
         accept(visitor: Visitor) is