validate provided table property values to prevent V panics (#32)

* check that data is not empty

* ensure tabsize of at least 2

* validate padding

* provide a default value for Table.custom_style

* add test for the validation function

termtable.v

@@ -34,10 +34,14 @@ pub mut:
 	align        Alignment = .left
 	padding      int = 1
 	tabsize      int = 4
-	custom_style StyleConfig
+	custom_style StyleConfig = StyleConfig{}
 }
 
 pub fn (t Table) str() string {
+	validate_table_properties(t) or {
+		eprintln('termtable: $err')
+		exit(1)
+	}
 	edata := expand_tabs(t.data, t.tabsize)
 	rowdata, coldata := get_row_and_col_data(edata, t.orientation)
 	colmaxes := max_column_sizes(coldata)
@@ -68,6 +72,18 @@ pub fn (t Table) str() string {
 	return final_str.trim_space()
 }
 
+fn validate_table_properties(t Table) ? {
+	if t.data == [][]string{} {
+		return error('Table.data should not be empty.')
+	}
+	if t.tabsize < 2 {
+		return error('tabsize should be at least 2 (got $t.tabsize).')
+	}
+	if t.padding < 0 {
+		return error('cannot use a negative padding (got $t.padding).')
+	}
+}
+
 fn expand_tabs(raw_data [][]string, tabsize int) [][]string {
 	mut edata := [][]string{}
 	for d in raw_data {

termtable_test.v

@@ -1,5 +1,32 @@
 module termtable
 
+fn test_validate_table_properties() {
+	tables := {
+		'no_data': Table{}
+		'small_tab': Table{
+			data: [['Foo\t']]
+			tabsize: 1
+		}
+		'negative_pad': Table{
+			data: [['Foo']]
+			padding: -1
+		}
+	}
+	error_suffixes := {
+		'no_data': 'Table.data should not be empty.'
+		'small_tab': 'tabsize should be at least 2 (got 1).'
+		'negative_pad': 'cannot use a negative padding (got -1).'
+	}
+	mut errors := 0
+	for k, t in tables {
+		validate_table_properties(t) or {
+			errors++
+			assert err == error_suffixes[k]
+		}
+	}
+	assert errors == tables.len
+}
+
 fn test_expand_tabs() {
 	tabs := [
 		['\tName', 'Sex\t\t'],