toml: isolate, fix and regress-test sumtype cast causing memory corruption (#12329)

vlib/toml/any.v

@@ -21,7 +21,11 @@ pub type Any = Null
 // string returns `Any` as a string.
 pub fn (a Any) string() string {
 	match a {
-		string { return a as string }
+		// NOTE if `.clone()` is not used here:
+		// string { return a as string }
+		// ... certain call-patterns to this function will cause a memory corruption.
+		// See `tests/toml_memory_corruption_test.v` for a matching regression test.
+		string { return (a as string).clone() }
 		time.Time { return a.format_ss_micro() }
 		else { return a.str() }
 	}

vlib/toml/tests/compact_test.v

@@ -35,18 +35,13 @@ fn test_parse_compact_text() {
 	assert title == toml.Any('TOML Example')
 	assert title as string == 'TOML Example'
 
-	owner := toml_doc.value('owner') as map[string]toml.Any
-	any_name := owner.value('name') or { panic(err) }
-	assert any_name.string() == 'Tom Preston-Werner'
-
 	database := toml_doc.value('database') as map[string]toml.Any
 	db_serv := database['server'] or {
 		panic('could not access "server" index in "database" variable')
 	}
 	assert db_serv as string == '192.168.1.1'
 
-	// TODO BUG depending on WHAT directory the tests is run from, this one assert sometimes fail?!?!
-	// assert toml_doc.value('owner.name') as string == 'Tom Preston-Werner'
+	assert toml_doc.value('owner.name') as string == 'Tom Preston-Werner'
 
 	assert toml_doc.value('database.server') as string == '192.168.1.1'
 

vlib/toml/tests/toml_memory_corruption_test.v

@@ -0,0 +1,24 @@
+// This tests the `toml` module for a known memory corruption.
+// The BUG shows below if no string `.clone()` nor any garbage-collection is done...
+import os
+import toml
+
+const toml_text = os.read_file(os.real_path(os.join_path(os.dir(@FILE), 'testdata', 'toml_test')) +
+	'.toml') or { panic(err) }
+
+fn test_toml_known_memory_corruption() {
+	toml_doc := toml.parse(toml_text) or { panic(err) }
+
+	owner := toml_doc.value('owner') as map[string]toml.Any
+	any_name := owner.value('name') or { panic(err) }
+	// This assert code path will cause the corruption.
+	assert any_name.string() == 'Tom Preston-Werner'
+
+	// This code then triggered the bug before the fix.
+	// Also see note in toml/any.v in function `pub fn (a Any) string() string`
+	assert toml_doc.value('owner.name') as string == 'Tom Preston-Werner'
+
+	// Repeat the pattern
+	assert any_name.string() == 'Tom Preston-Werner'
+	assert toml_doc.value('owner.name') as string == 'Tom Preston-Werner'
+}

vlib/toml/tests/toml_test.v

@@ -24,18 +24,13 @@ fn test_toml() {
 	assert title == toml.Any('TOML Example')
 	assert title as string == 'TOML Example'
 
-	owner := toml_doc.value('owner') as map[string]toml.Any
-	any_name := owner.value('name') or { panic(err) }
-	assert any_name.string() == 'Tom Preston-Werner'
-
 	database := toml_doc.value('database') as map[string]toml.Any
 	db_serv := database['server'] or {
 		panic('could not access "server" index in "database" variable')
 	}
 	assert db_serv as string == '192.168.1.1'
 
-	// TODO BUG depending on WHAT directory the tests is run from, this one assert sometimes fail?!?!
-	// assert toml_doc.value('owner.name') as string == 'Tom Preston-Werner'
+	assert toml_doc.value('owner.name') as string == 'Tom Preston-Werner'
 
 	assert toml_doc.value('database.server') as string == '192.168.1.1'
 

vlib/toml/toml.v

@@ -92,7 +92,6 @@ pub fn (d Doc) to_json() string {
 // value queries a value from the TOML document.
 pub fn (d Doc) value(key string) Any {
 	values := d.ast.table as map[string]ast.Value
-	// any_values := d.ast_to_any(values) as map[string]Any
 	return d.get_map_value_as_any(values, key)
 }