Fixed a file loading bug not covered by the mycology test suite

pkg/field/field.go

@@ -36,13 +36,19 @@ func Load(fd io.Reader) (*Field, error) {
 		data := make([]byte, 4096)
 		if n, errRead := fd.Read(data); errRead != nil {
 			if errRead == io.EOF {
-				if f.ly == 0 && l.l == 0 {
-					return nil, newDecodeError("No instruction on the first line of the file produces an unusable program in Befunge98")
+				if f.ly == 0 {
+					if l.l == 0 {
+						return nil, newDecodeError("No instruction on the first line of the file produces an unusable program in Befunge98")
+					}
+					f.x = l.x
 				}
 				if l.l > 0 {
 					f.ly++
-					if f.lx-f.x < l.l-l.x {
-						f.lx = l.l - l.x + f.x
+					if f.x < l.x {
+						f.x = l.x
+					}
+					if f.lx < l.l+l.x-f.x {
+						f.lx = l.l + l.x - f.x
 					}
 					f.lines = append(f.lines, *l)
 				}
@@ -56,12 +62,18 @@ func Load(fd io.Reader) (*Field, error) {
 					continue
 				}
 				if data[i] == '\n' || data[i] == '\r' {
-					if f.ly == 0 && l.l == 0 {
-						return nil, newDecodeError("No instruction on the first line of the file produces an unusable program in Befunge98")
+					if f.ly == 0 {
+						if l.l == 0 {
+							return nil, newDecodeError("No instruction on the first line of the file produces an unusable program in Befunge98")
+						}
+						f.x = l.x
 					}
 					f.ly++
-					if f.lx < l.l {
-						f.lx = l.l
+					if f.x > l.x {
+						f.x = l.x
+					}
+					if f.lx < l.l+l.x-f.x {
+						f.lx = l.l + l.x - f.x
 					}
 					f.lines = append(f.lines, *l)
 					l = new(Line)

pkg/field/field_test.go

@@ -38,6 +38,21 @@ func TestLoad(t *testing.T) {
 			},
 		},
 	}
+	// hello2 b98 file
+	hello2Field := Field{
+		x:  1,
+		y:  0,
+		lx: 33,
+		ly: 2,
+		lines: []Line{
+			Line{x: 33, l: 1, columns: []int{'v'}},
+			Line{
+				x:       1,
+				l:       33,
+				columns: []int{'@', ' ', '>', ' ', '#', ';', '>', ':', '#', ',', '_', 'e', '-', 'j', ';', ' ', '"', 'H', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', '!', '"', 'd', 'a', '<'},
+			},
+		},
+	}
 	// factorial b98 file
 	factorialField := Field{
 		x:  0,
@@ -134,6 +149,7 @@ func TestLoad(t *testing.T) {
 		{"io error", "test_data/minimal.b98", iotest.TimeoutReader, nil, &ReadError{}},
 		{"minimal", "test_data/minimal.b98", nil, &minimalField, nil},
 		{"hello", "test_data/hello.b98", nil, &helloField, nil},
+		{"hello2", "test_data/hello2.b98", nil, &hello2Field, nil},
 		{"factorial", "test_data/factorial.b98", nil, &factorialField, nil},
 		{"dna", "test_data/dna.b98", nil, &dnaField, nil},
 		{"\\r\\n file", "test_data/rn.b98", nil, &rnField, nil},

pkg/field/test_data/hello2.b98

@@ -0,0 +1,2 @@
+                                 v
+ @ > #;>:#,_e-j; "Hello world!"da<