fix(imports): Cache the error too in importAST().

imports.go

@@ -98,17 +98,22 @@ func MakeContentsRaw(bytes []byte) Contents {
 // It also verifies that the content pointer is the same for two foundAt values.
 type importCache struct {
 	foundAtVerification map[string]Contents
-	astCache            map[string]ast.Node
+	astCache            map[string]astCacheEntry
 	codeCache           map[string]potentialValue
 	importer            Importer
 }
 
+type astCacheEntry struct {
+	node ast.Node
+	err  error
+}
+
 // makeImportCache creates an importCache using an Importer.
 func makeImportCache(importer Importer) *importCache {
 	return &importCache{
 		importer:            importer,
 		foundAtVerification: make(map[string]Contents),
-		astCache:            make(map[string]ast.Node),
+		astCache:            make(map[string]astCacheEntry),
 		codeCache:           make(map[string]potentialValue),
 	}
 }
@@ -137,11 +142,11 @@ func (cache *importCache) importAST(importedFrom, importedPath string) (ast.Node
 	if err != nil {
 		return nil, "", err
 	}
-	if cachedNode, isCached := cache.astCache[foundAt]; isCached {
-		return cachedNode, foundAt, nil
+	if entry, isCached := cache.astCache[foundAt]; isCached {
+		return entry.node, foundAt, entry.err
 	}
 	node, err := program.SnippetToAST(ast.DiagnosticFileName(foundAt), foundAt, contents.String())
-	cache.astCache[foundAt] = node
+	cache.astCache[foundAt] = astCacheEntry{node: node, err: err}
 	return node, foundAt, err
 }
 

main_test.go

@@ -517,3 +517,20 @@ func TestEvalUnusualFilenames(t *testing.T) {
 		})
 	}
 }
+
+func TestEvalCachedErrorTwice(t *testing.T) {
+	// Evaluate the same erroneous file twice in the same VM.
+	// See https://github.com/google/go-jsonnet/issues/822
+	vm := MakeVM()
+	_, err1 := vm.EvaluateFile("testdata/syntax_error.jsonnet")
+	if err1 == nil {
+		t.Fatal("expected an error")
+	}
+	_, err2 := vm.EvaluateFile("testdata/syntax_error.jsonnet")
+	if err2 == nil {
+		t.Fatal("expected an error")
+	}
+	if err1.Error() != err2.Error() {
+		t.Fatalf("different error on the second run:\n1st: %q\n2nd: %q", err1, err2)
+	}
+}