[hcledit/read] fallback to raw values if unparsable (#100)

* [hcledit/read] fallback to raw values if unparsable

* [hcledit/read] add option to give clients ability to enable fallback behavior

* [hcledit/read] add flag to CLI command to control this behavior

cmd/hcledit/internal/command/fixture/file.tf

@@ -15,6 +15,9 @@ module "my-module" {
     "f",
   ]
 
+  unevaluateable_reference = var.name
+  unevaluateable_interpolation = "this-${local.reference}"
+
   map_variable = {
     bool_variable   = true
     int_variable    = 1

cmd/hcledit/internal/command/read.go

@@ -15,6 +15,7 @@ import (
 
 type ReadOptions struct {
 	OutputFormat string
+	Fallback     bool
 }
 
 func NewCmdRead() *cobra.Command {
@@ -36,6 +37,7 @@ func NewCmdRead() *cobra.Command {
 	}
 
 	cmd.Flags().StringVarP(&opts.OutputFormat, "output-format", "o", "go-template='{{.Value}}'", "format to print the value as")
+	cmd.Flags().BoolVar(&opts.Fallback, "fallback", false, "falls back to reading the raw value if it cannot be evaluated")
 
 	return cmd
 }
@@ -48,7 +50,11 @@ func runRead(opts *ReadOptions, args []string) (string, error) {
 		return "", fmt.Errorf("failed to read file: %s", err)
 	}
 
-	results, err := editor.Read(query)
+	readOpts:= []hcledit.Option{}
+	if opts.Fallback {
+		readOpts = append(readOpts, hcledit.WithReadFallbackToRawString())
+	}
+	results, err := editor.Read(query, readOpts...)
 	if err != nil {
 		return "", fmt.Errorf("failed to read file: %s", err)
 	}

cmd/hcledit/internal/command/read_test.go

@@ -95,6 +95,22 @@ func TestRunRead(t *testing.T) {
 			want:  "",
 			opts:  defaultOpts,
 		},
+		"unevaluateable reference fallback": {
+			query: "module.my-module.unevaluateable_reference",
+			want:  "var.name",
+			opts: &ReadOptions{
+				OutputFormat: "go-template='{{.Value}}'",
+				Fallback:     true,
+			},
+		},
+		"unevaluateable interpolation fallback": {
+			query: "module.my-module.unevaluateable_interpolation",
+			want:  `"this-${local.reference}"`,
+			opts: &ReadOptions{
+				OutputFormat: "go-template='{{.Value}}'",
+				Fallback:     true,
+			},
+		},
 	}
 
 	for name, tc := range cases {

hcledit.go

@@ -89,7 +89,7 @@ func (h *HCLEditor) Read(queryStr string, opts ...Option) (map[string]interface{
 	}
 
 	results := make(map[string]cty.Value)
-	hdlr, err := handler.NewReadHandler(results)
+	hdlr, err := handler.NewReadHandler(results, opt.readFallbackToRawString)
 	if err != nil {
 		return nil, err
 	}

hcledit_test.go

@@ -190,15 +190,17 @@ object1 = {
 
 func TestRead(t *testing.T) {
 	cases := map[string]struct {
-		input string
-		query string
-		want  map[string]interface{}
+		input   string
+		query   string
+		options []hcledit.Option
+		want    map[string]interface{}
 	}{
 		"Attribute": {
 			input: `
 attribute = "R"
 `,
 			query: "attribute",
+			options: make([]hcledit.Option, 0),
 			want: map[string]interface{}{
 				"attribute": "R",
 			},
@@ -211,6 +213,7 @@ block "label1" "label2" {
   attribute = "str"
 }
 `,
+			options: make([]hcledit.Option, 0),
 			query: "block",
 			want:  map[string]interface{}{},
 		},
@@ -221,6 +224,7 @@ block "label1" "label2" {
   attribute = "R"
 }
 `,
+			options: make([]hcledit.Option, 0),
 			query: "block.label1.label2.attribute",
 			want: map[string]interface{}{
 				"block.label1.label2.attribute": "R",
@@ -235,6 +239,7 @@ block1 "label1" "label2" {
   }
 }
 `,
+			options: make([]hcledit.Option, 0),
 			query: "block1.label1.label2.block2.label3.label4.attribute",
 			want: map[string]interface{}{
 				"block1.label1.label2.block2.label3.label4.attribute": "R",
@@ -252,6 +257,7 @@ block "label" "label2" {
 }
 
 `,
+			options: make([]hcledit.Option, 0),
 			query: "block.label.*.attribute",
 			want: map[string]interface{}{
 				"block.label.label1.attribute": "R",
@@ -265,6 +271,7 @@ object = {
   attribute = "R"
 }
 `,
+			options: make([]hcledit.Option, 0),
 			query: "object.attribute",
 			want: map[string]interface{}{
 				"object.attribute": "R",
@@ -278,6 +285,7 @@ object1 = {
   }  
 }
 `,
+			options: make([]hcledit.Option, 0),
 			query: "object1.object2.attribute",
 			want: map[string]interface{}{
 				"object1.object2.attribute": "R",
@@ -288,6 +296,7 @@ object1 = {
 			input: `
 attribute = 1
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": 1,
@@ -298,6 +307,7 @@ attribute = 1
 			input: `
 attribute = "str"
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": "str",
@@ -308,6 +318,7 @@ attribute = "str"
 			input: `
 attribute = true
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": true,
@@ -318,6 +329,7 @@ attribute = true
 			input: `
 attribute = false
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": false,
@@ -328,6 +340,7 @@ attribute = false
 			input: `
 attribute = ["str1", "str2", "str3"]
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": []string{"str1", "str2", "str3"},
@@ -338,6 +351,7 @@ attribute = ["str1", "str2", "str3"]
 			input: `
 attribute = [1, 2, 3]
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": []int{1, 2, 3},
@@ -348,11 +362,34 @@ attribute = [1, 2, 3]
 			input: `
 attribute = [true, false, true]
 `,
+			options: make([]hcledit.Option, 0),
 			query: "attribute",
 			want: map[string]interface{}{
 				"attribute": []bool{true, false, true},
 			},
 		},
+
+		"fallback to absolute variable name": {
+			input: `
+attribute = local.var
+`,
+			options: []hcledit.Option{hcledit.WithReadFallbackToRawString()},
+			query: "attribute",
+			want: map[string]interface{}{
+				"attribute": "local.var",
+			},
+		},
+
+		"fallback to uninterpolated string": {
+			input: `
+attribute = "some-${local.var}"
+`,
+			options: []hcledit.Option{hcledit.WithReadFallbackToRawString()},
+			query: "attribute",
+			want: map[string]interface{}{
+				"attribute": `"some-${local.var}"`,
+			},
+		},
 	}
 
 	for name, tc := range cases {
@@ -363,7 +400,7 @@ attribute = [true, false, true]
 				t.Fatal(err)
 			}
 
-			got, err := editor.Read(tc.query)
+			got, err := editor.Read(tc.query, tc.options...)
 			if err != nil {
 				t.Fatal(err)
 			}

internal/handler/read.go

@@ -12,18 +12,20 @@ import (
 )
 
 type readHandler struct {
-	results map[string]cty.Value
+	results             map[string]cty.Value
+	fallbackToRawString bool
 }
 
-func NewReadHandler(results map[string]cty.Value) (Handler, error) {
+func NewReadHandler(results map[string]cty.Value, fallbackToRawString bool) (Handler, error) {
 	return &readHandler{
-		results: results,
+		results:             results,
+		fallbackToRawString: fallbackToRawString,
 	}, nil
 }
 
 func (h *readHandler) HandleBody(body *hclwrite.Body, name string, keyTrail []string) error {
 	buf := body.GetAttribute(name).BuildTokens(nil).Bytes()
-	value, err := parse(buf, name)
+	value, err := parse(buf, name, h.fallbackToRawString)
 	if err != nil {
 		return err
 	}
@@ -33,24 +35,31 @@ func (h *readHandler) HandleBody(body *hclwrite.Body, name string, keyTrail []st
 
 func (h *readHandler) HandleObject(object *ast.Object, name string, keyTrail []string) error {
 	buf := object.GetObjectAttribute(name).BuildTokens().Bytes()
-	value, err := parse(buf, name)
+	value, err := parse(buf, name, h.fallbackToRawString)
 	if err != nil {
 		return err
 	}
 	h.results[strings.Join(keyTrail, ".")] = value
 	return nil
 }
 
-func parse(buf []byte, name string) (cty.Value, error) {
+func parse(buf []byte, name string, fallback bool) (cty.Value, error) {
 	file, diags := hclsyntax.ParseConfig(buf, "", hcl.Pos{Line: 1, Column: 1})
 	if diags.HasErrors() {
 		return cty.Value{}, diags
 	}
 
 	body := file.Body.(*hclsyntax.Body)
-	v, diags := body.Attributes[name].Expr.Value(nil)
+	expr := body.Attributes[name].Expr
+	v, diags := expr.Value(nil)
 	if diags.HasErrors() {
-		return cty.Value{}, diags
+		if !fallback {
+			return cty.Value{}, diags
+		}
+
+		// Could not parse the value with a nil EvalContext, so this is likely an
+		// interpolated string. Instead, attempt to parse the raw string value.
+		return cty.StringVal(string(expr.Range().SliceBytes(buf))), nil
 	}
 	return v, nil
 }

option.go

@@ -1,9 +1,10 @@
 package hcledit
 
 type option struct {
-	comment       string
-	afterKey      string
-	beforeNewline bool
+	comment                 string
+	afterKey                string
+	beforeNewline           bool
+	readFallbackToRawString bool
 }
 
 // Option configures specific behavior for specific HCLEditor operations.
@@ -30,3 +31,9 @@ func WithNewLine() Option {
 		opt.beforeNewline = true
 	}
 }
+
+func WithReadFallbackToRawString() Option {
+	return func(opt *option) {
+		opt.readFallbackToRawString = true
+	}
+}