100% compatibility with the BurntSushi tests established.

Makefile

@@ -1,9 +1,11 @@
-all:
+all: build
+
+build:
 	@(cd cmd/toml-test-decoder; go build)
 
 test:
-	@(cd ast; go test)
-	@(cd parse; go test)
+	@(cd ast; go test | grep -v ^PASS)
+	@(cd parse; go test | grep -v ^PASS)
 
-sushi-test:
+sushi-test: build
 	@(cd cmd/toml-test-decoder; go build; ${GOPATH}/bin/toml-test ./toml-test-decoder)

ast/ast.go

@@ -69,10 +69,10 @@ const (
 	TypeBoolean ValueType = "boolean"
 
 	// TypeOffsetDateTime identifies a date/time value, including timezone info (2019-06-18 10:32:15.173645362+0200).
-	TypeOffsetDateTime ValueType = "offset datetime"
+	TypeOffsetDateTime ValueType = "datetime"
 
 	// TypeLocalDateTime identifies a date/time value, without timezone info (2018-12-25 12:12:18.876772533).
-	TypeLocalDateTime ValueType = "datetime"
+	TypeLocalDateTime ValueType = "datetime-local"
 
 	// TypeLocalDate identifies a date value (2017-05-17).
 	TypeLocalDate ValueType = "date"
@@ -81,13 +81,18 @@ const (
 	TypeLocalTime ValueType = "time"
 
 	// TypeArrayOfTables identifies an [[array.of.tables]].
-	TypeArrayOfTables ValueType = "arrayOfTables"
+	TypeArrayOfTables ValueType = "array-of-tables"
 
 	// TypeArray identifies ["an", "inline", "static", "array"].
 	TypeArray ValueType = "array"
 
 	// TypeTable identifies an { "inline" = "table" } or [standard.table].
 	TypeTable ValueType = "table"
+
+	// TypeImplicitTable identifies an intermediate table that was created
+	// using a table definition that looks like [a.b.c.d] (where a, b and c
+	// would be implicit tables when they hadn't been created explicitly before).
+	TypeImplicitTable ValueType = "implicit-table"
 )
 
 // SetKeyValuePair is used to set a key and an accompanying value in the
@@ -115,22 +120,30 @@ func (doc *Document) OpenTable(key Key) error {
 	doc.CurrentKey = nil
 	doc.Current = doc.Root
 	// Go over all requested levels of the key. For all levels, except the last
-	// one, it is okay if a Table or TableArray already exists. For at least the
-	// last level, no table or value must exist, because that would mean we are
-	// overwriting an existing key/value pair, which is not allowed.
+	// one, it is okay if a Table, implicit Table or TableArray already exists.
+	// For at least the last level, no table or value must exist, or an implicit
+	// table must exist. Otherwise we are overwriting an existing value, which
+	// is not allowed.
 	node, lastKeyPart, err := doc.makeTablePath(key)
 	if err != nil {
 		return fmt.Errorf("invalid table: %s", err)
 	}
-	// Check if the key is still free for use.
+	// Check if the key is already in use.
 	if existing, ok := node[lastKeyPart]; ok {
-		path := doc.formatKeyPath(key, len(key)-1)
-		return fmt.Errorf("invalid table: %s value already exists at key %s", existing.Type, path)
+		// It is, but it is an implicit table. Upgrade it to an explicit and use it.
+		if existing.Type == TypeImplicitTable {
+			existing.Type = TypeTable
+			node = existing.Data[0].(Table)
+		} else {
+			path := doc.formatKeyPath(key, len(key)-1)
+			return fmt.Errorf("invalid table: %s value already exists at key %s", existing.Type, path)
+		}
+	} else {
+		// The subtable does not exist yet. Create the subtable.
+		subTable := make(Table)
+		node[lastKeyPart] = NewValue(TypeTable, subTable)
+		node = subTable
 	}
-	// The subtable does not exist yet. Create the subtable.
-	subTable := make(Table)
-	node[lastKeyPart] = NewValue(TypeTable, subTable)
-	node = subTable
 
 	// From here on, key/value pairs are added to the newly defined table.
 	doc.Current = node
@@ -193,10 +206,10 @@ func (doc *Document) makeTablePath(key Key) (Table, string, error) {
 		}
 		if subValue, ok := node[keyPart]; ok {
 			// You cannot overwrite an already defined key, regardless its value.
-			// When a value already exists at the current key, this can only be a table
-			// or an array of tables. In case of an array of tables, the last created
-			// table will be used.
-			if subValue.Type == TypeTable {
+			// When a value already exists at the current key, this can only be a table,
+			// an implicit table or an array of tables. In case of an array of tables,
+			// the table that was added last to the array will be used.
+			if subValue.Type == TypeTable || subValue.Type == TypeImplicitTable {
 				// A table was found, traverse to that table.
 				node = subValue.Data[0].(Table)
 			} else if subValue.Type == TypeArrayOfTables {
@@ -209,9 +222,9 @@ func (doc *Document) makeTablePath(key Key) (Table, string, error) {
 				return nil, "", fmt.Errorf("%s value already exists at key %s", subValue.Type, path)
 			}
 		} else {
-			// The subtable does not exist yet. Create the subtable.
+			// The subtable does not exist yet. Create the subtable as an implicit table.
 			subTable := make(Table)
-			node[keyPart] = NewValue(TypeTable, subTable)
+			node[keyPart] = NewValue(TypeImplicitTable, subTable)
 			node = subTable
 		}
 	}

ast/ast_test.go

@@ -73,9 +73,9 @@ func Test_ConstructExplicitTableAfterImplicitSubtable(t *testing.T) {
 		p := ast.NewDocument()
 		p.OpenTable(ast.NewKey("a", "b", "c"))
 		p.SetKeyValuePair(ast.NewKey("answer"), ast.NewValue(ast.TypeString, "42"))
-		p.OpenTable(ast.NewKey("a"))
+		err := p.OpenTable(ast.NewKey("a"))
 		p.SetKeyValuePair(ast.NewKey("better"), ast.NewValue(ast.TypeString, "43"))
-		return nil, p
+		return err, p
 	},
 		"",
 		`{"a": {"b": {"c": {"answer": "42"}}, "better": "43"}}`)

ast/string.go

@@ -35,6 +35,8 @@ func (value Value) String() string {
 			values[i] = value.(*Value).String()
 		}
 		return fmt.Sprintf("[%s]", strings.Join(values, ", "))
+	case TypeImplicitTable:
+		fallthrough
 	case TypeTable:
 		pairs := value.Data[0].(Table)
 		keys := make([]string, len(pairs))

cmd/toml-test-decoder/main.go

@@ -77,6 +77,8 @@ func makeSushi(value *ast.Value) string {
 		} else {
 			return fmt.Sprintf(`{"type": "array", "value": [%s]}`, strings.Join(values, ", "))
 		}
+	case ast.TypeImplicitTable:
+		fallthrough
 	case ast.TypeTable:
 		pairs := value.Data[0].(ast.Table)
 		keys := make([]string, len(pairs))

parse/value_array_test.go

@@ -39,7 +39,7 @@ func TestArray(t *testing.T) {
 		{`x=[[1],['a']]`, `{"x": [[1], ["a"]]}`, ``},
 		{`x=[[[],[]],[]]`, `{"x": [[[], []], []]}`, ``},
 		{"x=[\r\n\r\n \t\n [\r\n\r\n\t  [],[\t]],\t\n[]\t \t \n   ]", `{"x": [[[], []], []]}`, ``},
-		{`x=[[1],'a']`, `{}`, `type mismatch in array of static arrays: found an item of type string at line 1, column 11`},
+		{`x=[[1],'a']`, `{}`, `type mismatch in array of arrays: found an item of type string at line 1, column 11`},
 	} {
 		p := newParser()
 		testParse(t, p, p.startDocument, test)