command/format: indicate in diff when adding an attribute forces replacement

command/format/diff.go

@@ -253,6 +253,9 @@ func (p *blockBodyDiffPrinter) writeAttrDiff(name string, attrS *configschema.At
 		switch {
 		case showJustNew:
 			p.writeValue(new, action, indent+2)
+			if p.pathForcesNewResource(path) {
+				p.buf.WriteString(p.color.Color(forcesNewResourceCaption))
+			}
 		default:
 			// We show new even if it is null to emphasize the fact
 			// that it is being unset, since otherwise it is easy to

command/format/diff_test.go

@@ -327,6 +327,62 @@ new line
       ~ ami = "ami-BEFORE" -> "ami-AFTER" # forces replacement
       ~ id  = "i-02ae66f368e8518a9" -> (known after apply)
     }
+`,
+		},
+		"force replacement with empty before value": {
+			Action: plans.DeleteThenCreate,
+			Mode:   addrs.ManagedResourceMode,
+			Before: cty.ObjectVal(map[string]cty.Value{
+				"name":   cty.StringVal("name"),
+				"forced": cty.NullVal(cty.String),
+			}),
+			After: cty.ObjectVal(map[string]cty.Value{
+				"name":   cty.StringVal("name"),
+				"forced": cty.StringVal("example"),
+			}),
+			Schema: &configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"name":   {Type: cty.String, Optional: true},
+					"forced": {Type: cty.String, Optional: true},
+				},
+			},
+			RequiredReplace: cty.NewPathSet(cty.Path{
+				cty.GetAttrStep{Name: "forced"},
+			}),
+			Tainted: false,
+			ExpectedOutput: `  # test_instance.example must be replaced
+-/+ resource "test_instance" "example" {
+      + forced = "example" # forces replacement
+        name   = "name"
+    }
+`,
+		},
+		"force replacement with empty before value legacy": {
+			Action: plans.DeleteThenCreate,
+			Mode:   addrs.ManagedResourceMode,
+			Before: cty.ObjectVal(map[string]cty.Value{
+				"name":   cty.StringVal("name"),
+				"forced": cty.StringVal(""),
+			}),
+			After: cty.ObjectVal(map[string]cty.Value{
+				"name":   cty.StringVal("name"),
+				"forced": cty.StringVal("example"),
+			}),
+			Schema: &configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"name":   {Type: cty.String, Optional: true},
+					"forced": {Type: cty.String, Optional: true},
+				},
+			},
+			RequiredReplace: cty.NewPathSet(cty.Path{
+				cty.GetAttrStep{Name: "forced"},
+			}),
+			Tainted: false,
+			ExpectedOutput: `  # test_instance.example must be replaced
+-/+ resource "test_instance" "example" {
+      + forced = "example" # forces replacement
+        name   = "name"
+    }
 `,
 		},
 	}