don't panic on invalid keys for relevant attrs

The PathMatcher used when rendering diffs assumes the caller knows the
structure the path was derived from, which is incorrect.
RelevantAttributes is derived from references to an object, which may
have errors hidden by `try` or `can` functions, or the data may not have
been updated to match paths via targeted operations.

Even in the case where the data may be incorrect, we can't crash when
rendering the data, because the user may not be able to work around the
panic with no other information about which resource contains unexpected
references.

internal/command/jsonformat/structured/attribute_path/matcher.go

@@ -18,7 +18,7 @@ import (
 //
 // The caller of the above functions is required to know whether the next value
 // in the path is a list type or an object type and call the relevant function,
-// otherwise these functions will crash/panic.
+// otherwise no match will be returned.
 //
 // The Matches function returns true if the paths you have traversed until now
 // ends.
@@ -151,8 +151,18 @@ func (p *PathMatcher) GetChildWithKey(key string) Matcher {
 			continue
 		}
 
-		if path[0].(string) == key {
-			child.Paths = append(child.Paths, path[1:])
+		switch val := path[0].(type) {
+		case string:
+			if val == key {
+				child.Paths = append(child.Paths, path[1:])
+			}
+		case float64:
+			// here we must assume the path being looked up no longer matches
+			// the given data structure, so the caller in incorrect. This is
+			// fine, because it only means that we don't match any paths.
+		default:
+			panic(fmt.Errorf("found invalid type within path (%v:%T), the validation shouldn't have allowed this to happen; this is a bug in Terraform, please report it", val, val))
+
 		}
 	}
 	return child
@@ -190,15 +200,12 @@ func (p *PathMatcher) GetChildWithIndex(index int) Matcher {
 
 		switch val := path[0].(type) {
 		case float64:
-			if int(path[0].(float64)) == index {
+			if int(val) == index {
 				child.Paths = append(child.Paths, path[1:])
 			}
 		case string:
 			f, err := strconv.ParseFloat(val, 64)
-			if err != nil {
-				panic(fmt.Errorf("found invalid type within path (%v:%T), the validation shouldn't have allowed this to happen; this is a bug in Terraform, please report it", val, val))
-			}
-			if int(f) == index {
+			if err == nil && int(f) == index {
 				child.Paths = append(child.Paths, path[1:])
 			}
 		default:

internal/command/jsonformat/structured/attribute_path/matcher_test.go

@@ -254,3 +254,39 @@ func TestPathMatcher_MultiplePaths(t *testing.T) {
 		t.Errorf("should not have partial matched at leaf level")
 	}
 }
+
+// Since paths may be coming from relevant attributes, and those paths may no
+// longer correspond to an updated schema, we can't always be certain the caller
+// knows the correct type.
+func TestPathMatcher_WrongKeyTypes(t *testing.T) {
+	var matcher Matcher
+
+	matcher = &PathMatcher{
+		Paths: [][]interface{}{
+			{
+				float64(0),
+				"key",
+				float64(0),
+			},
+		},
+	}
+
+	failed := matcher.GetChildWithKey("key")
+	if failed.Matches() || failed.MatchesPartial() {
+		t.Errorf("should not have any match at on failure")
+	}
+
+	matcher = matcher.GetChildWithIndex(0).GetChildWithKey("key")
+
+	if matcher.Matches() {
+		t.Errorf("should not have exact matched at first level")
+	}
+	if !matcher.MatchesPartial() {
+		t.Errorf("should have partial matched at first level")
+	}
+
+	failed = matcher.GetChildWithKey("zero")
+	if failed.Matches() || failed.MatchesPartial() {
+		t.Errorf("should not have any match at on failure")
+	}
+}