checker: force all fn declarations to follow after all other top level statements (fix #25889) (#25890)

Author: spytheman

vlib/v/checker/checker.v

@@ -266,6 +266,7 @@ pub fn (mut c Checker) check(mut ast_file ast.File) {
 			}
 		}
 	}
+	c.reorder_fns_at_the_end(mut ast_file)
 	c.stmt_level = 0
 	for mut stmt in ast_file.stmts {
 		if stmt in [ast.ConstDecl, ast.ExprStmt] {
@@ -303,6 +304,31 @@ pub fn (mut c Checker) check(mut ast_file ast.File) {
 	c.check_unused_labels()
 }
 
+pub fn (mut c Checker) reorder_fns_at_the_end(mut ast_file ast.File) {
+	mut fdeclarations := 0
+	for mut stmt in ast_file.stmts {
+		if stmt is ast.FnDecl {
+			fdeclarations++
+		}
+	}
+	if fdeclarations == 0 {
+		return
+	}
+	// eprintln('>>> ast_file: ${ast_file.path:-60s} | fdeclarations: ${fdeclarations}')
+	mut stmts := []ast.Stmt{cap: ast_file.stmts.len}
+	for stmt in ast_file.stmts {
+		if stmt !is ast.FnDecl {
+			stmts << stmt
+		}
+	}
+	for stmt in ast_file.stmts {
+		if stmt is ast.FnDecl {
+			stmts << stmt
+		}
+	}
+	ast_file.stmts = stmts
+}
+
 pub fn (mut c Checker) check_scope_vars(sc &ast.Scope) {
 	if !c.pref.is_repl && !c.file.is_test {
 		for _, obj in sc.objects {

vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.out

@@ -3,6 +3,13 @@ vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:1:1: error: C struc
       | ~~~~~~~~~~~~
     2 |     ptr &T
     3 | }
+vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:9:1: error: JS structs cannot be declared as generic
+    7 | fn JS.encode[T](data string) T
+    8 | 
+    9 | struct JS.Some[T] {
+      | ~~~~~~~~~~~~~~
+   10 |     i T
+   11 | }
 vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:5:1: error: C functions cannot be declared as generic
     3 | }
     4 | 
@@ -17,10 +24,3 @@ vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:7:1: error: JS func
       | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     8 | 
     9 | struct JS.Some[T] {
-vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:9:1: error: JS structs cannot be declared as generic
-    7 | fn JS.encode[T](data string) T
-    8 | 
-    9 | struct JS.Some[T] {
-      | ~~~~~~~~~~~~~~
-   10 |     i T
-   11 | }

vlib/v/checker/tests/duplicate_field_method_err.out

@@ -1,13 +1,13 @@
+vlib/v/checker/tests/duplicate_field_method_err.vv:9:2: error: type `Foo` has both field and method named `bar`
+    7 | interface Foo {
+    8 |     bar fn ()
+    9 |     bar()
+      |     ~~~~~
+   10 | }
 vlib/v/checker/tests/duplicate_field_method_err.vv:5:1: error: type `St` has both field and method named `attr`
     3 | }
     4 | 
     5 | fn (s St) attr() {}
       | ~~~~~~~~~~~~~~~~
     6 | 
     7 | interface Foo {
-vlib/v/checker/tests/duplicate_field_method_err.vv:9:2: error: type `Foo` has both field and method named `bar`
-    7 | interface Foo {
-    8 |     bar fn ()
-    9 |     bar()
-      |     ~~~~~
-   10 | }

vlib/v/checker/tests/invalid_parameter_name_err.out

@@ -1,14 +1,14 @@
-vlib/v/checker/tests/invalid_parameter_name_err.vv:4:24: error: invalid use of reserved type `char` as a parameter name
-    2 | }
-    3 |
-    4 | fn (mut b Buffer) put8(char u8) ! {
-      |                        ~~~~
-    5 |     return error('-')
-    6 | }
 vlib/v/checker/tests/invalid_parameter_name_err.vv:10:6: error: invalid use of reserved type `char` as a parameter name
     8 | interface Writer {
     9 | mut:
    10 |     put(char u8) !
       |         ~~~~
    11 | }
    12 |
+vlib/v/checker/tests/invalid_parameter_name_err.vv:4:24: error: invalid use of reserved type `char` as a parameter name
+    2 | }
+    3 | 
+    4 | fn (mut b Buffer) put8(char u8) ! {
+      |                        ~~~~
+    5 |     return error('-')
+    6 | }

vlib/v/tests/fns/generic_fn_order_issue_25889_test.v

@@ -0,0 +1,35 @@
+interface Speaker {
+	speak()
+}
+
+struct Cat {}
+
+fn (c &Cat) speak() {}
+
+struct EventA {
+	a u32
+}
+
+struct EventB {
+	b u32
+}
+
+type Event = EventA | EventB
+
+fn some_func() {
+	queue := Queue.new[Speaker]()
+}
+
+struct Queue[T] {
+mut:
+	data &T = unsafe { nil }
+}
+
+fn Queue.new[T]() Queue[T] {
+	return Queue[T]{}
+}
+
+fn test_main() {
+	some_func()
+	assert true
+}