d2ir: Add more import error tests

d2ir/import.go

@@ -3,6 +3,7 @@ package d2ir
 import (
 	"bufio"
 	"path"
+	"strings"
 
 	"oss.terrastruct.com/d2/d2ast"
 	"oss.terrastruct.com/d2/d2parser"
@@ -15,9 +16,9 @@ func (c *compiler) pushImportStack(imp *d2ast.Import) bool {
 	}
 
 	newPath := imp.Path[0].Unbox().ScalarString()
-	for _, p := range c.importStack {
+	for i, p := range c.importStack {
 		if newPath == p {
-			c.errorf(imp, "detected cyclic import of %q", newPath)
+			c.errorf(imp, "detected cyclic import chain: %s", formatCyclicChain(c.importStack[i:]))
 			return false
 		}
 	}
@@ -30,6 +31,16 @@ func (c *compiler) popImportStack() {
 	c.importStack = c.importStack[:len(c.importStack)-1]
 }
 
+func formatCyclicChain(cyclicChain []string) string {
+	var b strings.Builder
+	for _, p := range cyclicChain {
+		b.WriteString(p)
+		b.WriteString(" -> ")
+	}
+	b.WriteString(cyclicChain[0])
+	return b.String()
+}
+
 // Returns either *Map or *Field.
 func (c *compiler) _import(imp *d2ast.Import) (Node, bool) {
 	ir, ok := c.__import(imp)

d2ir/import_test.go

@@ -3,8 +3,9 @@ package d2ir_test
 import (
 	"testing"
 
-	"oss.terrastruct.com/d2/d2ir"
 	"oss.terrastruct.com/util-go/assert"
+
+	"oss.terrastruct.com/d2/d2ir"
 )
 
 func testCompileImports(t *testing.T) {
@@ -89,7 +90,25 @@ label: meow`,
 	t.Run("errors", func(t *testing.T) {
 		tca := []testCase{
 			{
-				name: "parse_error",
+				name: "not_exist",
+				run: func(t testing.TB) {
+					_, err := compileFS(t, "index.d2", map[string]string{
+						"index.d2": "...@x.d2",
+					})
+					assert.ErrorString(t, err, `index.d2:1:1: failed to import "x.d2": open x.d2: no such file or directory`)
+				},
+			},
+			{
+				name: "absolute",
+				run: func(t testing.TB) {
+					_, err := compileFS(t, "index.d2", map[string]string{
+						"index.d2": "...@/x.d2",
+					})
+					assert.ErrorString(t, err, `index.d2:1:1: import paths must be relative`)
+				},
+			},
+			{
+				name: "parse",
 				run: func(t testing.TB) {
 					_, err := compileFS(t, "index.d2", map[string]string{
 						"index.d2": "...@x.d2",
@@ -103,6 +122,18 @@ x.d2:1:6: connection missing destination
 x.d2:1:7: connection missing source`)
 				},
 			},
+			{
+				name: "cyclic",
+				run: func(t testing.TB) {
+					_, err := compileFS(t, "index.d2", map[string]string{
+						"index.d2": "...@x",
+						"x.d2":     "...@y",
+						"y.d2":     "...@q",
+						"q.d2":     "...@x",
+					})
+					assert.ErrorString(t, err, `q.d2:1:1: detected cyclic import chain: x -> y -> q -> x`)
+				},
+			},
 		}
 		runa(t, tca)
 	})