parser, checker: fix generic fn variable assignment in generic fn (#18180)

vlib/v/checker/assign.v

@@ -182,6 +182,10 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 				if right.op == .amp && right.right is ast.StructInit {
 					right_type = c.expr(right)
 				}
+			} else if mut right is ast.Ident {
+				if right.kind == .function {
+					c.expr(right)
+				}
 			}
 			if right.is_auto_deref_var() {
 				left_type = ast.mktyp(right_type.deref())

vlib/v/checker/checker.v

@@ -3238,6 +3238,12 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 		return typ
 	} else if node.kind == .function {
 		info := node.info as ast.IdentFn
+		if func := c.table.find_fn(node.name) {
+			if func.generic_names.len > 0 {
+				concrete_types := node.concrete_types.map(c.unwrap_generic(it))
+				c.table.register_fn_concrete_types(func.fkey(), concrete_types)
+			}
+		}
 		return info.typ
 	} else if node.kind == .unresolved {
 		// first use
@@ -3394,11 +3400,12 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 			mut fn_type := ast.new_type(c.table.find_or_register_fn_type(func, false,
 				true))
 			if func.generic_names.len > 0 {
+				concrete_types := node.concrete_types.map(c.unwrap_generic(it))
 				if typ_ := c.table.resolve_generic_to_concrete(fn_type, func.generic_names,
-					node.concrete_types)
+					concrete_types)
 				{
 					fn_type = typ_
-					c.table.register_fn_concrete_types(func.fkey(), node.concrete_types)
+					c.table.register_fn_concrete_types(func.fkey(), concrete_types)
 				}
 			}
 			node.name = name

vlib/v/parser/parser.v

@@ -2131,7 +2131,7 @@ fn (mut p Parser) is_following_concrete_types() bool {
 		} else if cur_tok.kind == .rsbr {
 			break
 		} else if cur_tok.kind == .name {
-			if !(cur_tok.lit.len > 1 && p.is_typename(cur_tok)) {
+			if !(p.is_typename(cur_tok) && !(cur_tok.lit.len == 1 && !cur_tok.lit[0].is_capital())) {
 				return false
 			}
 		} else if cur_tok.kind != .comma {

vlib/v/tests/generics_fn_variable_2_test.v

@@ -0,0 +1,26 @@
+fn g[T]() u32 {
+	return sizeof(T)
+}
+
+fn f[T]() u32 {
+	p := g[T]
+	return p()
+}
+
+fn test_generic_fn_variable() {
+	r1 := f[int]()
+	println(r1)
+	assert r1 == 4
+
+	r2 := f[string]()
+	println(r2)
+	assert r2 == 16
+
+	r3 := f[f64]()
+	println(r3)
+	assert r3 == 8
+
+	r4 := f[bool]()
+	println(r4)
+	assert r4 == 1
+}