Add support for lists in the structured renderer (#32401)

* prep for processing the structured run output

* undo unwanted change to a json key

* Add skeleton functions and API for refactored renderer

* goimports

* Fix documentation of the RenderOpts struct

* Add rendering functionality for primitives to the structured renderer

* add test case for override

* Add support for parsing and rendering sensitive values in the renderer

* Add support for unknown/computed values in the structured renderer

* delete missing unit tests

* Add support for object attributes in the structured renderer

* goimports

* Add support for the replace paths data in the structured renderer

* Add support for maps in the structured renderer

* Add support for lists in the structured renderer

* goimports

* add additional comments explaining

internal/command/jsonformat/change/list.go

@@ -0,0 +1,120 @@
+package change
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/hashicorp/terraform/internal/command/format"
+	"github.com/hashicorp/terraform/internal/plans"
+)
+
+func List(elements []Change) Renderer {
+	return &listRenderer{
+		displayContext: true,
+		elements:       elements,
+	}
+}
+
+func NestedList(elements []Change) Renderer {
+	return &listRenderer{
+		elements: elements,
+	}
+}
+
+type listRenderer struct {
+	NoWarningsRenderer
+
+	// displayContext tells the renderer to display additional information about
+	// the before and after index values within a given list. For example, index
+	//
+	displayContext bool
+	elements       []Change
+}
+
+func (renderer listRenderer) Render(change Change, indent int, opts RenderOpts) string {
+	if len(renderer.elements) == 0 {
+		return fmt.Sprintf("[]%s%s", change.nullSuffix(opts.overrideNullSuffix), change.forcesReplacement())
+	}
+
+	elementOpts := opts.Clone()
+	elementOpts.overrideNullSuffix = true
+
+	unchangedElementOpts := opts.Clone()
+	unchangedElementOpts.showUnchangedChildren = true
+
+	var unchangedElements []Change
+
+	// renderNext tells the renderer to print out the next element in the list
+	// whatever state it is in. So, even if a change is a NoOp we will still
+	// print it out if the last change we processed wants us to.
+	renderNext := false
+
+	var buf bytes.Buffer
+	buf.WriteString(fmt.Sprintf("[%s\n", change.forcesReplacement()))
+	for _, element := range renderer.elements {
+		if element.action == plans.NoOp && !renderNext && !opts.showUnchangedChildren {
+			unchangedElements = append(unchangedElements, element)
+			continue
+		}
+		renderNext = false
+
+		// If we want to display the context around this change, we want to
+		// render the change immediately before this change in the list, and the
+		// change immediately after in the list, even if both these changes are
+		// NoOps. This will give the user reading the diff some context as to
+		// where in the list these changes are being made, as order matters.
+		if renderer.displayContext {
+			// If our list of unchanged elements contains more than one entry
+			// we'll print out a count of the number of unchanged elements that
+			// we skipped. Note, this is the length of the unchanged elements
+			// minus 1 as the most recent unchanged element will be printed out
+			// in full.
+			if len(unchangedElements) > 1 {
+				buf.WriteString(fmt.Sprintf("%s%s %s\n", change.indent(indent+1), change.emptySymbol(), change.unchanged("element", len(unchangedElements)-1)))
+			}
+			// If our list of unchanged elements contains at least one entry,
+			// we're going to print out the most recent change in full. That's
+			// what happens here.
+			if len(unchangedElements) > 0 {
+				lastElement := unchangedElements[len(unchangedElements)-1]
+				buf.WriteString(fmt.Sprintf("%s    %s,\n", change.indent(indent+1), lastElement.Render(indent+1, unchangedElementOpts)))
+			}
+			// We now reset the unchanged elements list, we've printed out a
+			// count of all the elements we skipped so we start counting from
+			// scratch again. This means that if we process a run of changed
+			// elements, they won't all start printing out summaries of every
+			// change that happened previously.
+			unchangedElements = nil
+
+			// As we also want to render the element immediately after any
+			// changes, we make a note here to say we should render the next
+			// change whatever it is. But, we only want to render the next
+			// change if the current change isn't a NoOp. If the current change
+			// is a NoOp then it was told to print by the last change and we
+			// don't want to cascade and print all changes from now on.
+			renderNext = element.action != plans.NoOp
+		}
+
+		for _, warning := range element.Warnings(indent + 1) {
+			buf.WriteString(fmt.Sprintf("%s%s\n", change.indent(indent+1), warning))
+		}
+		if element.action == plans.NoOp {
+			buf.WriteString(fmt.Sprintf("%s    %s,\n", change.indent(indent+1), element.Render(indent+1, unchangedElementOpts)))
+		} else {
+			buf.WriteString(fmt.Sprintf("%s%s %s,\n", change.indent(indent+1), format.DiffActionSymbol(element.action), element.Render(indent+1, elementOpts)))
+		}
+	}
+
+	// If we were not displaying any context alongside our changes then the
+	// unchangedElements list will contain every unchanged element, and we'll
+	// print that out as we do with every other collection.
+	//
+	// If we were displaying context, then this will contain any unchanged
+	// elements since our last change, so we should also print it out.
+	if len(unchangedElements) > 0 {
+		buf.WriteString(fmt.Sprintf("%s%s %s\n", change.indent(indent+1), change.emptySymbol(), change.unchanged("element", len(unchangedElements))))
+	}
+
+	buf.WriteString(fmt.Sprintf("%s%s ]%s", change.indent(indent), change.emptySymbol(), change.nullSuffix(opts.overrideNullSuffix)))
+	return buf.String()
+}

internal/command/jsonformat/change/renderer_test.go

@@ -518,6 +518,24 @@ func TestRenderers(t *testing.T) {
 {
       ~ "element_one" = (sensitive)
     }
+`,
+		},
+		"map_update_sensitive_element_status": {
+			change: Change{
+				renderer: Map(map[string]Change{
+					"element_one": {
+						renderer: Sensitive(0, 0, true, false),
+						action:   plans.Update,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+{
+      # Warning: this attribute value will no longer be marked as sensitive
+      # after applying this change. The value is unchanged.
+      ~ "element_one" = (sensitive)
+    }
 `,
 		},
 		"map_delete_sensitive_element": {
@@ -569,6 +587,308 @@ func TestRenderers(t *testing.T) {
 {
       ~ "element_one" = 1 -> (known after apply)
     }
+`,
+		},
+		"list_create_empty": {
+			change: Change{
+				renderer: List([]Change{}),
+				action:   plans.Create,
+			},
+			expected: "[]",
+		},
+		"list_create": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(nil, strptr("1")),
+						action:   plans.Create,
+					},
+				}),
+				action: plans.Create,
+			},
+			expected: `
+[
+      + 1,
+    ]
+`,
+		},
+		"list_delete_empty": {
+			change: Change{
+				renderer: List([]Change{}),
+				action:   plans.Delete,
+			},
+			expected: "[] -> null",
+		},
+		"list_delete": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(strptr("1"), nil),
+						action:   plans.Delete,
+					},
+				}),
+				action: plans.Delete,
+			},
+			expected: `
+[
+      - 1,
+    ] -> null
+`,
+		},
+		"list_create_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(nil, strptr("1")),
+						action:   plans.Create,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      + 1,
+    ]
+`,
+		},
+		"list_update_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(strptr("0"), strptr("1")),
+						action:   plans.Update,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      ~ 0 -> 1,
+    ]
+`,
+		},
+		"list_replace_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(strptr("0"), nil),
+						action:   plans.Delete,
+					},
+					{
+						renderer: Primitive(nil, strptr("1")),
+						action:   plans.Create,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      - 0,
+      + 1,
+    ]
+`,
+		},
+		"list_delete_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(strptr("0"), nil),
+						action:   plans.Delete,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      - 0,
+    ]
+`,
+		},
+		"list_update_forces_replacement": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(strptr("0"), strptr("1")),
+						action:   plans.Update,
+					},
+				}),
+				action:  plans.Update,
+				replace: true,
+			},
+			expected: `
+[ # forces replacement
+      ~ 0 -> 1,
+    ]
+`,
+		},
+		"list_update_ignores_unchanged": {
+			change: Change{
+				renderer: NestedList([]Change{
+					{
+						renderer: Primitive(strptr("0"), strptr("0")),
+						action:   plans.NoOp,
+					},
+					{
+						renderer: Primitive(strptr("1"), strptr("1")),
+						action:   plans.NoOp,
+					},
+					{
+						renderer: Primitive(strptr("2"), strptr("5")),
+						action:   plans.Update,
+					},
+					{
+						renderer: Primitive(strptr("3"), strptr("3")),
+						action:   plans.NoOp,
+					},
+					{
+						renderer: Primitive(strptr("4"), strptr("4")),
+						action:   plans.NoOp,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      ~ 2 -> 5,
+        # (4 unchanged elements hidden)
+    ]
+`,
+		},
+		"list_update_ignored_unchanged_with_context": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Primitive(strptr("0"), strptr("0")),
+						action:   plans.NoOp,
+					},
+					{
+						renderer: Primitive(strptr("1"), strptr("1")),
+						action:   plans.NoOp,
+					},
+					{
+						renderer: Primitive(strptr("2"), strptr("5")),
+						action:   plans.Update,
+					},
+					{
+						renderer: Primitive(strptr("3"), strptr("3")),
+						action:   plans.NoOp,
+					},
+					{
+						renderer: Primitive(strptr("4"), strptr("4")),
+						action:   plans.NoOp,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+        # (1 unchanged element hidden)
+        1,
+      ~ 2 -> 5,
+        3,
+        # (1 unchanged element hidden)
+    ]
+`,
+		},
+		"list_create_sensitive_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Sensitive(nil, 1, false, true),
+						action:   plans.Create,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      + (sensitive),
+    ]
+`,
+		},
+		"list_delete_sensitive_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Sensitive(1, nil, true, false),
+						action:   plans.Delete,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      - (sensitive),
+    ]
+`,
+		},
+		"list_update_sensitive_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Sensitive(nil, 1, false, true),
+						action:   plans.Update,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      ~ (sensitive),
+    ]
+`,
+		},
+		"list_update_sensitive_element_status": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Sensitive(1, 1, false, true),
+						action:   plans.Update,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      # Warning: this attribute value will be marked as sensitive and will not
+      # display in UI output after applying this change. The value is unchanged.
+      ~ (sensitive),
+    ]
+`,
+		},
+		"list_create_computed_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Computed(Change{}),
+						action:   plans.Create,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      + (known after apply),
+    ]
+`,
+		},
+		"list_update_computed_element": {
+			change: Change{
+				renderer: List([]Change{
+					{
+						renderer: Computed(Change{
+							renderer: Primitive(strptr("0"), nil),
+							action:   plans.Delete,
+						}),
+						action: plans.Update,
+					},
+				}),
+				action: plans.Update,
+			},
+			expected: `
+[
+      ~ 0 -> (known after apply),
+    ]
 `,
 		},
 	}

internal/command/jsonformat/change/testing.go

@@ -126,6 +126,50 @@ func ValidateMap(elements map[string]ValidateChangeFunc, action plans.Action, re
 	}
 }
 
+func ValidateList(elements []ValidateChangeFunc, action plans.Action, replace bool) ValidateChangeFunc {
+	return func(t *testing.T, change Change) {
+		validateChange(t, change, action, replace)
+
+		list, ok := change.renderer.(*listRenderer)
+		if !ok {
+			t.Fatalf("invalid renderer type: %T", change.renderer)
+		}
+
+		if !list.displayContext {
+			t.Fatalf("created the wrong type of list renderer")
+		}
+
+		validateList(t, list, elements)
+	}
+}
+
+func ValidateNestedList(elements []ValidateChangeFunc, action plans.Action, replace bool) ValidateChangeFunc {
+	return func(t *testing.T, change Change) {
+		validateChange(t, change, action, replace)
+
+		list, ok := change.renderer.(*listRenderer)
+		if !ok {
+			t.Fatalf("invalid renderer type: %T", change.renderer)
+		}
+
+		if list.displayContext {
+			t.Fatalf("created the wrong type of list renderer")
+		}
+
+		validateList(t, list, elements)
+	}
+}
+
+func validateList(t *testing.T, list *listRenderer, elements []ValidateChangeFunc) {
+	if len(list.elements) != len(elements) {
+		t.Fatalf("expected %d elements but found %d elements", len(elements), len(list.elements))
+	}
+
+	for ix := 0; ix < len(elements); ix++ {
+		elements[ix](t, list.elements[ix])
+	}
+}
+
 func ValidateSensitive(before, after interface{}, beforeSensitive, afterSensitive bool, action plans.Action, replace bool) ValidateChangeFunc {
 	return func(t *testing.T, change Change) {
 		validateChange(t, change, action, replace)

internal/command/jsonformat/differ/attribute.go

@@ -21,6 +21,8 @@ func (v Value) computeChangeForNestedAttribute(attribute *jsonprovider.NestedTyp
 		return v.computeAttributeChangeAsNestedObject(attribute.Attributes)
 	case "map":
 		return v.computeAttributeChangeAsNestedMap(attribute.Attributes)
+	case "list":
+		return v.computeAttributeChangeAsNestedList(attribute.Attributes)
 	default:
 		panic("unrecognized nesting mode: " + attribute.NestingMode)
 	}
@@ -34,8 +36,10 @@ func (v Value) computeChangeForType(ctyType cty.Type) change.Change {
 		return v.computeAttributeChangeAsObject(ctyType.AttributeTypes())
 	case ctyType.IsMapType():
 		return v.computeAttributeChangeAsMap(ctyType.ElementType())
+	case ctyType.IsListType():
+		return v.computeAttributeChangeAsList(ctyType.ElementType())
 	default:
-		panic("not implemented")
+		panic("unrecognized type: " + ctyType.FriendlyName())
 	}
 }
 

internal/command/jsonformat/differ/list.go

@@ -0,0 +1,165 @@
+package differ
+
+import (
+	"reflect"
+
+	"github.com/zclconf/go-cty/cty"
+
+	"github.com/hashicorp/terraform/internal/command/jsonformat/change"
+	"github.com/hashicorp/terraform/internal/command/jsonprovider"
+)
+
+func (v Value) computeAttributeChangeAsList(elementType cty.Type) change.Change {
+	var elements []change.Change
+	current := v.getDefaultActionForIteration()
+	v.processList(elementType, func(value Value) {
+		element := value.ComputeChange(elementType)
+		elements = append(elements, element)
+		current = compareActions(current, element.GetAction())
+	})
+	return change.New(change.List(elements), current, v.replacePath())
+}
+
+func (v Value) computeAttributeChangeAsNestedList(attributes map[string]*jsonprovider.Attribute) change.Change {
+	var elements []change.Change
+	current := v.getDefaultActionForIteration()
+	v.processNestedList(func(value Value) {
+		element := value.ComputeChange(attributes)
+		elements = append(elements, element)
+		current = compareActions(current, element.GetAction())
+	})
+	return change.New(change.NestedList(elements), current, v.replacePath())
+}
+
+func (v Value) processNestedList(process func(value Value)) {
+	sliceValue := v.asSlice()
+	for ix := 0; ix < len(sliceValue.Before) || ix < len(sliceValue.After); ix++ {
+		process(sliceValue.getChild(ix, ix, false))
+	}
+}
+
+func (v Value) processList(elementType cty.Type, process func(value Value)) {
+	sliceValue := v.asSlice()
+
+	lcs := lcs(sliceValue.Before, sliceValue.After)
+	var beforeIx, afterIx, lcsIx int
+	for beforeIx < len(sliceValue.Before) || afterIx < len(sliceValue.After) || lcsIx < len(lcs) {
+		// Step through all the before values until we hit the next item in the
+		// longest common subsequence. We are going to just say that all of
+		// these have been deleted.
+		for beforeIx < len(sliceValue.Before) && (lcsIx >= len(lcs) || !reflect.DeepEqual(sliceValue.Before[beforeIx], lcs[lcsIx])) {
+			isObjectDiff := elementType.IsObjectType() && afterIx < len(sliceValue.After) && (lcsIx >= len(lcs) || !reflect.DeepEqual(sliceValue.After[afterIx], lcs[lcsIx]))
+			if isObjectDiff {
+				process(sliceValue.getChild(beforeIx, afterIx, false))
+				beforeIx++
+				afterIx++
+				continue
+			}
+
+			process(sliceValue.getChild(beforeIx, len(sliceValue.After), false))
+			beforeIx++
+		}
+
+		// Now, step through all the after values until hit the next item in the
+		// LCS. We are going to say that all of these have been created.
+		for afterIx < len(sliceValue.After) && (lcsIx >= len(lcs) || !reflect.DeepEqual(sliceValue.After[afterIx], lcs[lcsIx])) {
+			process(sliceValue.getChild(len(sliceValue.Before), afterIx, false))
+			afterIx++
+		}
+
+		// Finally, add the item in common as unchanged.
+		if lcsIx < len(lcs) {
+			process(sliceValue.getChild(beforeIx, afterIx, false))
+			beforeIx++
+			afterIx++
+			lcsIx++
+		}
+	}
+}
+
+func lcs(xs, ys []interface{}) []interface{} {
+	if len(xs) == 0 || len(ys) == 0 {
+		return make([]interface{}, 0)
+	}
+
+	c := make([]int, len(xs)*len(ys))
+	eqs := make([]bool, len(xs)*len(ys))
+	w := len(xs)
+
+	for y := 0; y < len(ys); y++ {
+		for x := 0; x < len(xs); x++ {
+			eq := false
+			if reflect.DeepEqual(xs[x], ys[y]) {
+				eq = true
+				eqs[(w*y)+x] = true // equality tests can be expensive, so cache it
+			}
+			if eq {
+				// Sequence gets one longer than for the cell at top left,
+				// since we'd append a new item to the sequence here.
+				if x == 0 || y == 0 {
+					c[(w*y)+x] = 1
+				} else {
+					c[(w*y)+x] = c[(w*(y-1))+(x-1)] + 1
+				}
+			} else {
+				// We follow the longest of the sequence above and the sequence
+				// to the left of us in the matrix.
+				l := 0
+				u := 0
+				if x > 0 {
+					l = c[(w*y)+(x-1)]
+				}
+				if y > 0 {
+					u = c[(w*(y-1))+x]
+				}
+				if l > u {
+					c[(w*y)+x] = l
+				} else {
+					c[(w*y)+x] = u
+				}
+			}
+		}
+	}
+
+	// The bottom right cell tells us how long our longest sequence will be
+	seq := make([]interface{}, c[len(c)-1])
+
+	// Now we will walk back from the bottom right cell, finding again all
+	// of the equal pairs to construct our sequence.
+	x := len(xs) - 1
+	y := len(ys) - 1
+	i := len(seq) - 1
+
+	for x > -1 && y > -1 {
+		if eqs[(w*y)+x] {
+			// Add the value to our result list and then walk diagonally
+			// up and to the left.
+			seq[i] = xs[x]
+			x--
+			y--
+			i--
+		} else {
+			// Take the path with the greatest sequence length in the matrix.
+			l := 0
+			u := 0
+			if x > 0 {
+				l = c[(w*y)+(x-1)]
+			}
+			if y > 0 {
+				u = c[(w*(y-1))+x]
+			}
+			if l > u {
+				x--
+			} else {
+				y--
+			}
+		}
+	}
+
+	if i > -1 {
+		// should never happen if the matrix was constructed properly
+		panic("not enough elements in sequence")
+	}
+
+	return seq
+}

internal/command/jsonformat/differ/map.go

@@ -1,9 +1,10 @@
 package differ
 
 import (
+	"github.com/zclconf/go-cty/cty"
+
 	"github.com/hashicorp/terraform/internal/command/jsonformat/change"
 	"github.com/hashicorp/terraform/internal/command/jsonprovider"
-	"github.com/zclconf/go-cty/cty"
 )
 
 func (v Value) computeAttributeChangeAsMap(elementType cty.Type) change.Change {

internal/command/jsonformat/differ/value_map.go

@@ -61,6 +61,9 @@ func (m ValueMap) processReplacePaths(key string) []interface{} {
 		path := p.([]interface{})
 
 		if len(path) == 0 {
+			// This means that the current value is causing a replacement but
+			// not its children, so we skip as we are returning the child's
+			// value.
 			continue
 		}
 

internal/command/jsonformat/differ/value_slice.go

@@ -0,0 +1,96 @@
+package differ
+
+type ValueSlice struct {
+	// Before contains the value before the proposed change.
+	Before []interface{}
+
+	// After contains the value after the proposed change.
+	After []interface{}
+
+	// Unknown contains the unknown status of any elements of this list/set.
+	Unknown []interface{}
+
+	// BeforeSensitive contains the before sensitive status of any elements of
+	//this list/set.
+	BeforeSensitive []interface{}
+
+	// AfterSensitive contains the after sensitive status of any elements of
+	//this list/set.
+	AfterSensitive []interface{}
+
+	// ReplacePaths matches the same attributes in Value exactly.
+	ReplacePaths []interface{}
+}
+
+func (v Value) asSlice() ValueSlice {
+	return ValueSlice{
+		Before:          genericToSlice(v.Before),
+		After:           genericToSlice(v.After),
+		Unknown:         genericToSlice(v.Unknown),
+		BeforeSensitive: genericToSlice(v.BeforeSensitive),
+		AfterSensitive:  genericToSlice(v.AfterSensitive),
+		ReplacePaths:    v.ReplacePaths,
+	}
+}
+
+func (s ValueSlice) getChild(beforeIx, afterIx int, propagateReplace bool) Value {
+	before, beforeExplicit := getFromGenericSlice(s.Before, beforeIx)
+	after, afterExplicit := getFromGenericSlice(s.After, afterIx)
+	unknown, _ := getFromGenericSlice(s.Unknown, afterIx)
+	beforeSensitive, _ := getFromGenericSlice(s.BeforeSensitive, beforeIx)
+	afterSensitive, _ := getFromGenericSlice(s.AfterSensitive, afterIx)
+
+	return Value{
+		BeforeExplicit:  beforeExplicit,
+		AfterExplicit:   afterExplicit,
+		Before:          before,
+		After:           after,
+		Unknown:         unknown,
+		BeforeSensitive: beforeSensitive,
+		AfterSensitive:  afterSensitive,
+		ReplacePaths:    s.processReplacePaths(beforeIx, propagateReplace),
+	}
+}
+
+func (s ValueSlice) processReplacePaths(ix int, propagateReplace bool) []interface{} {
+	var ret []interface{}
+	for _, p := range s.ReplacePaths {
+		path := p.([]interface{})
+
+		if len(path) == 0 {
+			// This means that the current value is causing a replacement but
+			// not its children. Normally, we'd skip this as we do with maps
+			// but sets display the replace suffix on all their children even
+			// if they themselves are specified, so we want to pass this on.
+			if propagateReplace {
+				ret = append(ret, path)
+			}
+			// If we don't want to propagate the replace we just skip over this
+			// entry. If we do, we've added it to the returned set of paths
+			// already, so we still want to skip over the rest of this.
+			continue
+		}
+
+		if int(path[0].(float64)) == ix {
+			ret = append(ret, path[1:])
+		}
+	}
+	return ret
+}
+
+func getFromGenericSlice(generic []interface{}, ix int) (interface{}, bool) {
+	if generic == nil {
+		return nil, false
+	}
+	if ix < 0 || ix >= len(generic) {
+		return nil, false
+	}
+	return generic[ix], true
+}
+
+func genericToSlice(generic interface{}) []interface{} {
+	if concrete, ok := generic.([]interface{}); ok {
+		return concrete
+	}
+	return nil
+}

internal/command/jsonformat/differ/value_test.go

@@ -422,6 +422,34 @@ func TestValue_ObjectAttributes(t *testing.T) {
 				validate(t, input.ComputeChange(attribute))
 			})
 
+			t.Run("list", func(t *testing.T) {
+				attribute := &jsonprovider.Attribute{
+					AttributeType: unmarshalType(t, cty.List(cty.Object(tc.attributes))),
+				}
+
+				input := wrapValueInSlice(tc.input)
+
+				if tc.validateObject != nil {
+					validate := change.ValidateList([]change.ValidateChangeFunc{
+						tc.validateObject,
+					}, collectionDefaultAction, false)
+					validate(t, input.ComputeChange(attribute))
+					return
+				}
+
+				if tc.validateSingleChange != nil {
+					validate := change.ValidateList([]change.ValidateChangeFunc{
+						tc.validateSingleChange,
+					}, collectionDefaultAction, false)
+					validate(t, input.ComputeChange(attribute))
+					return
+				}
+
+				validate := change.ValidateList([]change.ValidateChangeFunc{
+					change.ValidateObject(tc.validateChanges, tc.validateAction, tc.validateReplace),
+				}, collectionDefaultAction, false)
+				validate(t, input.ComputeChange(attribute))
+			})
 		})
 
 		t.Run(fmt.Sprintf("nested_%s", name), func(t *testing.T) {
@@ -494,6 +522,46 @@ func TestValue_ObjectAttributes(t *testing.T) {
 				}, collectionDefaultAction, false)
 				validate(t, input.ComputeChange(attribute))
 			})
+
+			t.Run("list", func(t *testing.T) {
+				attribute := &jsonprovider.Attribute{
+					AttributeNestedType: &jsonprovider.NestedType{
+						Attributes: func() map[string]*jsonprovider.Attribute {
+							attributes := make(map[string]*jsonprovider.Attribute)
+							for key, attribute := range tc.attributes {
+								attributes[key] = &jsonprovider.Attribute{
+									AttributeType: unmarshalType(t, attribute),
+								}
+							}
+							return attributes
+						}(),
+						NestingMode: "list",
+					},
+				}
+
+				input := wrapValueInSlice(tc.input)
+
+				if tc.validateNestedObject != nil {
+					validate := change.ValidateNestedList([]change.ValidateChangeFunc{
+						tc.validateNestedObject,
+					}, collectionDefaultAction, false)
+					validate(t, input.ComputeChange(attribute))
+					return
+				}
+
+				if tc.validateSingleChange != nil {
+					validate := change.ValidateNestedList([]change.ValidateChangeFunc{
+						tc.validateSingleChange,
+					}, collectionDefaultAction, false)
+					validate(t, input.ComputeChange(attribute))
+					return
+				}
+
+				validate := change.ValidateNestedList([]change.ValidateChangeFunc{
+					change.ValidateNestedObject(tc.validateChanges, tc.validateAction, tc.validateReplace),
+				}, collectionDefaultAction, false)
+				validate(t, input.ComputeChange(attribute))
+			})
 		})
 	}
 }
@@ -504,9 +572,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 	// contexts of collections.
 
 	tcs := map[string]struct {
-		input          Value
-		attribute      cty.Type
-		validateChange change.ValidateChangeFunc
+		input               Value
+		attribute           cty.Type
+		validateChange      change.ValidateChangeFunc
+		validateListChanges []change.ValidateChangeFunc // Lists are special in some cases.
 	}{
 		"primitive_create": {
 			input: Value{
@@ -529,6 +598,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 			},
 			attribute:      cty.String,
 			validateChange: change.ValidatePrimitive(strptr("\"old\""), strptr("\"new\""), plans.Update, false),
+			validateListChanges: []change.ValidateChangeFunc{
+				change.ValidatePrimitive(strptr("\"old\""), nil, plans.Delete, false),
+				change.ValidatePrimitive(nil, strptr("\"new\""), plans.Create, false),
+			},
 		},
 		"primitive_set_explicit_null": {
 			input: Value{
@@ -538,6 +611,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 			},
 			attribute:      cty.String,
 			validateChange: change.ValidatePrimitive(strptr("\"old\""), nil, plans.Update, false),
+			validateListChanges: []change.ValidateChangeFunc{
+				change.ValidatePrimitive(strptr("\"old\""), nil, plans.Delete, false),
+				change.ValidatePrimitive(nil, nil, plans.Create, false),
+			},
 		},
 		"primitive_unset_explicit_null": {
 			input: Value{
@@ -547,6 +624,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 			},
 			attribute:      cty.String,
 			validateChange: change.ValidatePrimitive(nil, strptr("\"new\""), plans.Update, false),
+			validateListChanges: []change.ValidateChangeFunc{
+				change.ValidatePrimitive(nil, nil, plans.Delete, false),
+				change.ValidatePrimitive(nil, strptr("\"new\""), plans.Create, false),
+			},
 		},
 		"primitive_create_sensitive": {
 			input: Value{
@@ -575,6 +656,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 			},
 			attribute:      cty.String,
 			validateChange: change.ValidateSensitive("old", "new", true, true, plans.Update, false),
+			validateListChanges: []change.ValidateChangeFunc{
+				change.ValidateSensitive("old", nil, true, false, plans.Delete, false),
+				change.ValidateSensitive(nil, "new", false, true, plans.Create, false),
+			},
 		},
 		"primitive_create_computed": {
 			input: Value{
@@ -593,6 +678,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 			},
 			attribute:      cty.String,
 			validateChange: change.ValidateComputed(change.ValidatePrimitive(strptr("\"old\""), nil, plans.Delete, false), plans.Update, false),
+			validateListChanges: []change.ValidateChangeFunc{
+				change.ValidatePrimitive(strptr("\"old\""), nil, plans.Delete, false),
+				change.ValidateComputed(nil, plans.Create, false),
+			},
 		},
 		"primitive_update_replace": {
 			input: Value{
@@ -604,6 +693,10 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 			},
 			attribute:      cty.String,
 			validateChange: change.ValidatePrimitive(strptr("\"old\""), strptr("\"new\""), plans.Update, true),
+			validateListChanges: []change.ValidateChangeFunc{
+				change.ValidatePrimitive(strptr("\"old\""), nil, plans.Delete, true),
+				change.ValidatePrimitive(nil, strptr("\"new\""), plans.Create, false),
+			},
 		},
 		"noop": {
 			input: Value{
@@ -640,6 +733,24 @@ func TestValue_PrimitiveAttributes(t *testing.T) {
 				}, defaultCollectionsAction, false)
 				validate(t, input.ComputeChange(attribute))
 			})
+
+			t.Run("list", func(t *testing.T) {
+				input := wrapValueInSlice(tc.input)
+				attribute := &jsonprovider.Attribute{
+					AttributeType: unmarshalType(t, cty.List(tc.attribute)),
+				}
+
+				if tc.validateListChanges != nil {
+					validate := change.ValidateList(tc.validateListChanges, defaultCollectionsAction, false)
+					validate(t, input.ComputeChange(attribute))
+					return
+				}
+
+				validate := change.ValidateList([]change.ValidateChangeFunc{
+					tc.validateChange,
+				}, defaultCollectionsAction, false)
+				validate(t, input.ComputeChange(attribute))
+			})
 		})
 	}
 }
@@ -765,6 +876,108 @@ func TestValue_CollectionAttributes(t *testing.T) {
 			},
 			validateChange: change.ValidateComputed(change.ValidateMap(nil, plans.Delete, false), plans.Update, false),
 		},
+		"list_create_empty": {
+			input: Value{
+				Before: nil,
+				After:  []interface{}{},
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateList(nil, plans.Create, false),
+		},
+		"list_create_populated": {
+			input: Value{
+				Before: nil,
+				After:  []interface{}{"one", "two"},
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateList([]change.ValidateChangeFunc{
+				change.ValidatePrimitive(nil, strptr("\"one\""), plans.Create, false),
+				change.ValidatePrimitive(nil, strptr("\"two\""), plans.Create, false),
+			}, plans.Create, false),
+		},
+		"list_delete_empty": {
+			input: Value{
+				Before: []interface{}{},
+				After:  nil,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateList(nil, plans.Delete, false),
+		},
+		"list_delete_populated": {
+			input: Value{
+				Before: []interface{}{"one", "two"},
+				After:  nil,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateList([]change.ValidateChangeFunc{
+				change.ValidatePrimitive(strptr("\"one\""), nil, plans.Delete, false),
+				change.ValidatePrimitive(strptr("\"two\""), nil, plans.Delete, false),
+			}, plans.Delete, false),
+		},
+		"list_create_sensitive": {
+			input: Value{
+				Before:         nil,
+				After:          []interface{}{},
+				AfterSensitive: true,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateSensitive(nil, []interface{}{}, false, true, plans.Create, false),
+		},
+		"list_update_sensitive": {
+			input: Value{
+				Before:          []interface{}{"one"},
+				BeforeSensitive: true,
+				After:           []interface{}{},
+				AfterSensitive:  true,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateSensitive([]interface{}{"one"}, []interface{}{}, true, true, plans.Update, false),
+		},
+		"list_delete_sensitive": {
+			input: Value{
+				Before:          []interface{}{},
+				BeforeSensitive: true,
+				After:           nil,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateSensitive([]interface{}{}, nil, true, false, plans.Delete, false),
+		},
+		"list_create_unknown": {
+			input: Value{
+				Before:  nil,
+				After:   []interface{}{},
+				Unknown: true,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateComputed(nil, plans.Create, false),
+		},
+		"list_update_unknown": {
+			input: Value{
+				Before:  []interface{}{},
+				After:   []interface{}{"one"},
+				Unknown: true,
+			},
+			attribute: &jsonprovider.Attribute{
+				AttributeType: unmarshalType(t, cty.List(cty.String)),
+			},
+			validateChange: change.ValidateComputed(change.ValidateList(nil, plans.Delete, false), plans.Update, false),
+		},
 	}
 
 	for name, tc := range tcs {
@@ -785,10 +998,27 @@ func unmarshalType(t *testing.T, ctyType cty.Type) json.RawMessage {
 	return msg
 }
 
+// wrapValueInSlice does the same as wrapValueInMap, except it wraps it into a
+// slice internally.
+func wrapValueInSlice(input Value) Value {
+	return wrapValue(input, float64(0), func(value interface{}, unknown interface{}, explicit bool) interface{} {
+		switch value.(type) {
+		case nil:
+			if set, ok := unknown.(bool); (set && ok) || explicit {
+				return []interface{}{nil}
+
+			}
+			return []interface{}{}
+		default:
+			return []interface{}{value}
+		}
+	})
+}
+
 // wrapValueInMap access a single Value and returns a new Value that represents
 // a map with a single element. That single element is the input value.
 func wrapValueInMap(input Value) Value {
-	tomap := func(value interface{}, unknown interface{}, explicit bool) interface{} {
+	return wrapValue(input, "element", func(value interface{}, unknown interface{}, explicit bool) interface{} {
 		switch value.(type) {
 		case nil:
 			if set, ok := unknown.(bool); (set && ok) || explicit {
@@ -802,20 +1032,22 @@ func wrapValueInMap(input Value) Value {
 				"element": value,
 			}
 		}
-	}
+	})
+}
 
+func wrapValue(input Value, step interface{}, wrap func(interface{}, interface{}, bool) interface{}) Value {
 	return Value{
-		Before:          tomap(input.Before, nil, input.BeforeExplicit),
-		After:           tomap(input.After, input.Unknown, input.AfterExplicit),
-		Unknown:         tomap(input.Unknown, nil, false),
-		BeforeSensitive: tomap(input.BeforeSensitive, nil, false),
-		AfterSensitive:  tomap(input.AfterSensitive, nil, false),
+		Before:          wrap(input.Before, nil, input.BeforeExplicit),
+		After:           wrap(input.After, input.Unknown, input.AfterExplicit),
+		Unknown:         wrap(input.Unknown, nil, false),
+		BeforeSensitive: wrap(input.BeforeSensitive, nil, false),
+		AfterSensitive:  wrap(input.AfterSensitive, nil, false),
 		ReplacePaths: func() []interface{} {
 			var ret []interface{}
 			for _, path := range input.ReplacePaths {
 				old := path.([]interface{})
 				var updated []interface{}
-				updated = append(updated, "element")
+				updated = append(updated, step)
 				updated = append(updated, old...)
 				ret = append(ret, updated)
 			}