configs: support ignore_changes wildcards

The initial pass of implementation here missed the special case where
ignore_changes can, in the old parser, be set to ["*"] to ignore changes
to all attributes.

Since that syntax is awkward and non-obvious, our new decoder will instead
expect ignore_changes = all, using HCL2's capability to interpret an
expression as a literal keyword. For compatibility with old configurations
we will still accept the ["*"] form but emit a deprecation warning to
encourage moving to the new form.

configs/compat_shim.go

@@ -3,6 +3,7 @@ package configs
 import (
 	"github.com/hashicorp/hcl2/hcl"
 	"github.com/hashicorp/hcl2/hcl/hclsyntax"
+	"github.com/zclconf/go-cty/cty"
 )
 
 // -------------------------------------------------------------------------
@@ -79,3 +80,20 @@ func shimTraversalInString(expr hcl.Expression, wantKeyword bool) (hcl.Expressio
 		SrcRange:  srcRange,
 	}, diags
 }
+
+// shimIsIgnoreChangesStar returns true if the given expression seems to be
+// a string literal whose value is "*". This is used to support a legacy
+// form of ignore_changes = all .
+//
+// This function does not itself emit any diagnostics, so it's the caller's
+// responsibility to emit a warning diagnostic when this function returns true.
+func shimIsIgnoreChangesStar(expr hcl.Expression) bool {
+	val, valDiags := expr.Value(nil)
+	if valDiags.HasErrors() {
+		return false
+	}
+	if val.Type() != cty.String || val.IsNull() || !val.IsKnown() {
+		return false
+	}
+	return val.AsString() == "*"
+}

configs/parser_config_test.go

@@ -129,6 +129,16 @@ func TestParserLoadConfigFileFailureMessages(t *testing.T) {
 			hcl.DiagWarning,
 			"Quoted references are deprecated",
 		},
+		{
+			"valid-files/resources-ignorechanges-all-legacy.tf",
+			hcl.DiagWarning,
+			"Deprecated ignore_changes wildcard",
+		},
+		{
+			"valid-files/resources-ignorechanges-all-legacy.tf.json",
+			hcl.DiagWarning,
+			"Deprecated ignore_changes wildcard",
+		},
 		{
 			"valid-files/resources-provisioner-when-quoted.tf",
 			hcl.DiagWarning,

configs/resource.go

@@ -26,6 +26,7 @@ type ManagedResource struct {
 	CreateBeforeDestroy bool
 	PreventDestroy      bool
 	IgnoreChanges       []hcl.Traversal
+	IgnoreAllChanges    bool
 
 	CreateBeforeDestroySet bool
 	PreventDestroySet      bool
@@ -118,19 +119,66 @@ func decodeResourceBlock(block *hcl.Block) (*ManagedResource, hcl.Diagnostics) {
 			}
 
 			if attr, exists := lcContent.Attributes["ignore_changes"]; exists {
-				exprs, listDiags := hcl.ExprList(attr.Expr)
-				diags = append(diags, listDiags...)
 
-				for _, expr := range exprs {
+				// ignore_changes can either be a list of relative traversals
-					expr, shimDiags := shimTraversalInString(expr, false)
+				// or it can be just the keyword "all" to ignore changes to this
-					diags = append(diags, shimDiags...)
+				// resource entirely.
+				//   ignore_changes = [ami, instance_type]
+				//   ignore_changes = all
+				// We also allow two legacy forms for compatibility with earlier
+				// versions:
+				//   ignore_changes = ["ami", "instance_type"]
+				//   ignore_changes = ["*"]
 
-					traversal, travDiags := hcl.RelTraversalForExpr(expr)
+				kw := hcl.ExprAsKeyword(attr.Expr)
-					diags = append(diags, travDiags...)
+
-					if len(traversal) != 0 {
+				switch {
-						r.IgnoreChanges = append(r.IgnoreChanges, traversal)
+				case kw == "all":
+					r.IgnoreAllChanges = true
+				default:
+					exprs, listDiags := hcl.ExprList(attr.Expr)
+					diags = append(diags, listDiags...)
+
+					var ignoreAllRange hcl.Range
+
+					for _, expr := range exprs {
+
+						// our expr might be the literal string "*", which
+						// we accept as a deprecated way of saying "all".
+						if shimIsIgnoreChangesStar(expr) {
+							r.IgnoreAllChanges = true
+							ignoreAllRange = expr.Range()
+							diags = append(diags, &hcl.Diagnostic{
+								Severity: hcl.DiagWarning,
+								Summary:  "Deprecated ignore_changes wildcard",
+								Detail:   "The [\"*\"] form of ignore_changes wildcard is reprecated. Use \"ignore_changes = all\" to ignore changes to all attributes.",
+								Subject:  attr.Expr.Range().Ptr(),
+							})
+							continue
+						}
+
+						expr, shimDiags := shimTraversalInString(expr, false)
+						diags = append(diags, shimDiags...)
+
+						traversal, travDiags := hcl.RelTraversalForExpr(expr)
+						diags = append(diags, travDiags...)
+						if len(traversal) != 0 {
+							r.IgnoreChanges = append(r.IgnoreChanges, traversal)
+						}
 					}
+
+					if r.IgnoreAllChanges && len(r.IgnoreChanges) != 0 {
+						diags = append(diags, &hcl.Diagnostic{
+							Severity: hcl.DiagError,
+							Summary:  "Invalid ignore_changes ruleset",
+							Detail:   "Cannot mix wildcard string \"*\" with non-wildcard references.",
+							Subject:  &ignoreAllRange,
+							Context:  attr.Expr.Range().Ptr(),
+						})
+					}
+
 				}
+
 			}
 
 		case "connection":

configs/test-fixtures/invalid-files/resources-ignorechanges-all-legacymix.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "web" {
+  lifecycle {
+    ignore_changes = ["*", "foo"]
+  }
+}

configs/test-fixtures/valid-files/resources-ignorechanges-all-legacy.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "web" {
+  lifecycle {
+    ignore_changes = ["*"]
+  }
+}

configs/test-fixtures/valid-files/resources-ignorechanges-all-legacy.tf.json

@@ -0,0 +1,11 @@
+{
+  "resource": {
+    "aws_instance": {
+      "web": {
+        "lifecycle": {
+          "ignore_changes": ["*"]
+        }
+      }
+    }
+  }
+}

configs/test-fixtures/valid-files/resources-ignorechanges-all.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "web" {
+  lifecycle {
+    ignore_changes = all
+  }
+}

configs/test-fixtures/valid-files/resources-ignorechanges-all.tf.json

@@ -0,0 +1,11 @@
+{
+  "resource": {
+    "aws_instance": {
+      "web": {
+        "lifecycle": {
+          "ignore_changes": "all"
+        }
+      }
+    }
+  }
+}