toml: support arrays in value key query syntax (#12527)

vlib/toml/toml.v

@@ -156,28 +156,48 @@ pub fn (d Doc) to_any() Any {
 }
 
 // value queries a value from the TOML document.
-// `key` should be in "dotted" form (`a.b.c`).
-// `key` supports quoted keys like `a."b.c"`.
+// `key` supports a small query syntax scheme:
+// Maps can be queried in "dotted" form e.g. `a.b.c`.
+// quoted keys are supported as `a."b.c"` or `a.'b.c'`.
+// Arrays can be queried  with `a[0].b[1].[2]`.
 pub fn (d Doc) value(key string) Any {
-	values := d.ast.table as map[string]ast.Value
 	key_split := parse_dotted_key(key) or { return Any(Null{}) }
-	return d.value_(values, key_split)
+	return d.value_(d.ast.table, key_split)
 }
 
 // value_ returns the value found at `key` in the map `values` as `Any` type.
-fn (d Doc) value_(values map[string]ast.Value, key []string) Any {
-	value := values[key[0]] or {
-		return Any(Null{})
-		// TODO decide this
-		// panic(@MOD + '.' + @STRUCT + '.' + @FN + ' key "$key[0]" does not exist')
+fn (d Doc) value_(value ast.Value, key []string) Any {
+	assert key.len > 0
+	mut ast_value := ast.Value(ast.Null{})
+	mut index := -1
+	mut k := key[0]
+	if k.contains('[') {
+		index = k.all_after('[').all_before(']').int()
+		if k.starts_with('[') {
+			k = '' // k.all_after(']')
+		} else {
+			k = k.all_before('[')
+		}
+	}
+	if k == '' {
+		a := value as []ast.Value
+		ast_value = a[index] or { return Any(Null{}) }
+	}
+
+	if value is map[string]ast.Value {
+		ast_value = value[k] or { return Any(Null{}) }
+		if index > -1 {
+			a := ast_value as []ast.Value
+			ast_value = a[index] or { return Any(Null{}) }
+		}
+	}
+
+	if key.len <= 1 {
+		return d.ast_to_any(ast_value)
 	}
 	// `match` isn't currently very suitable for these types of sum type constructs...
-	if value is map[string]ast.Value {
-		if key.len <= 1 {
-			return d.ast_to_any(value)
-		}
-		m := (value as map[string]ast.Value)
-		return d.value_(m, key[1..])
+	if ast_value is map[string]ast.Value || ast_value is []ast.Value {
+		return d.value_(ast_value, key[1..])
 	}
 	return d.ast_to_any(value)
 }