trim index steps from RequiresNew paths

Only GetAttrSteps can actually trigger RequiresNew, but the flatmaps
paths will point to the indexed value that caused the change.

config/hcl2shim/paths.go

@@ -28,6 +28,10 @@ func RequiresReplace(attrs []string, ty cty.Type) ([]cty.Path, error) {
 		paths = append(paths, p)
 	}
 
+	// now trim off any trailing paths that aren't GetAttrSteps, since only an
+	// attribute itself can require replacement
+	paths = trimPaths(paths)
+
 	// There may be redundant paths due to set elements or index attributes
 	// Do some ugly n^2 filtering, but these are always fairly small sets.
 	for i := 0; i < len(paths)-1; i++ {
@@ -44,6 +48,30 @@ func RequiresReplace(attrs []string, ty cty.Type) ([]cty.Path, error) {
 	return paths, nil
 }
 
+// trimPaths removes any trailing steps that aren't of type GetAttrSet, since
+// only an attribute itself can require replacement
+func trimPaths(paths []cty.Path) []cty.Path {
+	var trimmed []cty.Path
+	for _, path := range paths {
+		path = trimPath(path)
+		if len(path) > 0 {
+			trimmed = append(trimmed, path)
+		}
+	}
+	return trimmed
+}
+
+func trimPath(path cty.Path) cty.Path {
+	for len(path) > 0 {
+		_, isGetAttr := path[len(path)-1].(cty.GetAttrStep)
+		if isGetAttr {
+			break
+		}
+		path = path[:len(path)-1]
+	}
+	return path
+}
+
 // requiresReplacePath takes a key from a flatmap along with the cty.Type
 // describing the structure, and returns the cty.Path that would be used to
 // reference the nested value in the data structure.

config/hcl2shim/paths_test.go

@@ -6,9 +6,18 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/google/go-cmp/cmp/cmpopts"
+
+	"github.com/google/go-cmp/cmp"
+
 	"github.com/zclconf/go-cty/cty"
 )
 
+var (
+	ignoreUnexported = cmpopts.IgnoreUnexported(cty.GetAttrStep{}, cty.IndexStep{})
+	valueComparer    = cmp.Comparer(cty.Value.RawEquals)
+)
+
 func TestPathFromFlatmap(t *testing.T) {
 	tests := []struct {
 		Flatmap string
@@ -221,3 +230,140 @@ func TestPathFromFlatmap(t *testing.T) {
 		})
 	}
 }
+
+func TestRequiresReplace(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		attrs    []string
+		expected []cty.Path
+		ty       cty.Type
+	}{
+		{
+			name: "basic",
+			attrs: []string{
+				"foo",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.String,
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}},
+			},
+		},
+		{
+			name: "two",
+			attrs: []string{
+				"foo",
+				"bar",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.String,
+				"bar": cty.String,
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}},
+				cty.Path{cty.GetAttrStep{Name: "bar"}},
+			},
+		},
+		{
+			name: "nested object",
+			attrs: []string{
+				"foo.bar",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.Object(map[string]cty.Type{
+					"bar": cty.String,
+				}),
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}, cty.GetAttrStep{Name: "bar"}},
+			},
+		},
+		{
+			name: "nested objects",
+			attrs: []string{
+				"foo.bar.baz",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.Object(map[string]cty.Type{
+					"bar": cty.Object(map[string]cty.Type{
+						"baz": cty.String,
+					}),
+				}),
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}, cty.GetAttrStep{Name: "bar"}, cty.GetAttrStep{Name: "baz"}},
+			},
+		},
+		{
+			name: "nested map",
+			attrs: []string{
+				"foo.%",
+				"foo.bar",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.Map(cty.String),
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}},
+			},
+		},
+		{
+			name: "nested list",
+			attrs: []string{
+				"foo.#",
+				"foo.1",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.Map(cty.String),
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}},
+			},
+		},
+		{
+			name: "object in map",
+			attrs: []string{
+				"foo.bar.baz",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.Map(cty.Object(
+					map[string]cty.Type{
+						"baz": cty.String,
+					},
+				)),
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}, cty.IndexStep{Key: cty.StringVal("bar")}, cty.GetAttrStep{Name: "baz"}},
+			},
+		},
+		{
+			name: "object in list",
+			attrs: []string{
+				"foo.1.baz",
+			},
+			ty: cty.Object(map[string]cty.Type{
+				"foo": cty.List(cty.Object(
+					map[string]cty.Type{
+						"baz": cty.String,
+					},
+				)),
+			}),
+			expected: []cty.Path{
+				cty.Path{cty.GetAttrStep{Name: "foo"}, cty.IndexStep{Key: cty.NumberIntVal(1)}, cty.GetAttrStep{Name: "baz"}},
+			},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			rp, err := RequiresReplace(tc.attrs, tc.ty)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !cmp.Equal(tc.expected, rp, ignoreUnexported, valueComparer) {
+				t.Fatalf("\nexpected: %#v\ngot: %#v\n", tc.expected, rp)
+			}
+		})
+
+	}
+
+}