all: Add support for write-only attributes

.changes/unreleased/FEATURES-20250121-165644.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'helper/schema: Added `WriteOnly` schema behavior for managed resource schemas to indicate a write-only attribute. 
+Write-only attributes are managed resource attributes whose values are not saved to the Terraform plan or state artifacts.'
+time: 2025-01-21T16:56:44.038893-05:00
+custom:
+    Issue: "1375"

.changes/unreleased/FEATURES-20250121-170105.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'helper/validation: Added `PreferWriteOnlyAttribute()` validator that warns practitioners when a write-only version of 
+a configured attribute is available.'
+time: 2025-01-21T17:01:05.40229-05:00
+custom:
+    Issue: "1375"

.changes/unreleased/NOTES-20250121-170545.yaml

@@ -0,0 +1,5 @@
+kind: NOTES
+body: Write-only attribute support is in technical preview and offered without compatibility promises until Terraform 1.11 is generally available.
+time: 2025-01-21T17:05:45.398836-05:00
+custom:
+    Issue: "1375"

go.mod

@@ -16,7 +16,7 @@ require (
 	github.com/hashicorp/logutils v1.0.0
 	github.com/hashicorp/terraform-exec v0.21.0
 	github.com/hashicorp/terraform-json v0.24.0
-	github.com/hashicorp/terraform-plugin-go v0.25.0
+	github.com/hashicorp/terraform-plugin-go v0.26.0
 	github.com/hashicorp/terraform-plugin-log v0.9.0
 	github.com/mitchellh/copystructure v1.2.0
 	github.com/mitchellh/go-testing-interface v1.14.1
@@ -38,7 +38,7 @@ require (
 	github.com/hashicorp/go-cleanhttp v0.5.2 // indirect
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
 	github.com/hashicorp/go-retryablehttp v0.7.7 // indirect
-	github.com/hashicorp/terraform-registry-address v0.2.3 // indirect
+	github.com/hashicorp/terraform-registry-address v0.2.4 // indirect
 	github.com/hashicorp/terraform-svchost v0.1.1 // indirect
 	github.com/hashicorp/yamux v0.1.1 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
@@ -49,13 +49,13 @@ require (
 	github.com/vmihailenco/msgpack/v5 v5.4.1 // indirect
 	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect
 	golang.org/x/mod v0.22.0 // indirect
-	golang.org/x/net v0.33.0 // indirect
+	golang.org/x/net v0.34.0 // indirect
 	golang.org/x/sync v0.10.0 // indirect
 	golang.org/x/sys v0.29.0 // indirect
 	golang.org/x/text v0.21.0 // indirect
 	golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d // indirect
 	google.golang.org/appengine v1.6.8 // indirect
-	google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 // indirect
-	google.golang.org/grpc v1.67.1 // indirect
-	google.golang.org/protobuf v1.35.1 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20241015192408-796eee8c2d53 // indirect
+	google.golang.org/grpc v1.69.4 // indirect
+	google.golang.org/protobuf v1.36.3 // indirect
 )

go.sum

@@ -29,6 +29,10 @@ github.com/go-git/go-billy/v5 v5.6.0 h1:w2hPNtoehvJIxR00Vb4xX94qHQi/ApZfX+nBE2Cj
 github.com/go-git/go-billy/v5 v5.6.0/go.mod h1:sFDq7xD3fn3E0GOwUSZqHo9lrkmx8xJhA0ZrfvjBRGM=
 github.com/go-git/go-git/v5 v5.13.0 h1:vLn5wlGIh/X78El6r3Jr+30W16Blk0CTcxTYcYPWi5E=
 github.com/go-git/go-git/v5 v5.13.0/go.mod h1:Wjo7/JyVKtQgUNdXYXIepzWfJQkUEIGvkvVkiXRR/zw=
+github.com/go-logr/logr v1.4.2 h1:6pFjapn8bFcIbiKo3XT4j/BhANplGihG6tvd+8rYgrY=
+github.com/go-logr/logr v1.4.2/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/go-test/deep v1.0.3 h1:ZrJSEWsXzPOxaZnFteGEfooLba+ju3FYIbOrS+rQd68=
 github.com/go-test/deep v1.0.3/go.mod h1:wGDj63lr65AM2AQyKZd/NYHGb0R+1RLqB8NKt3aSFNA=
 github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da h1:oI5xCqsCo564l8iNU+DwB5epxmsaqB+rhGL0m5jtYqE=
@@ -42,6 +46,8 @@ github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMyw
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/hashicorp/errwrap v1.0.0 h1:hLrqtEDnRye3+sgx6z4qVLNuviH3MR5aQ0ykNJa/UYA=
 github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-checkpoint v0.5.0 h1:MFYpPZCnQqQTE18jFwSII6eUQrD/oxMFp3mlgcqk5mU=
@@ -74,12 +80,12 @@ github.com/hashicorp/terraform-exec v0.21.0 h1:uNkLAe95ey5Uux6KJdua6+cv8asgILFVW
 github.com/hashicorp/terraform-exec v0.21.0/go.mod h1:1PPeMYou+KDUSSeRE9szMZ/oHf4fYUmB923Wzbq1ICg=
 github.com/hashicorp/terraform-json v0.24.0 h1:rUiyF+x1kYawXeRth6fKFm/MdfBS6+lW4NbeATsYz8Q=
 github.com/hashicorp/terraform-json v0.24.0/go.mod h1:Nfj5ubo9xbu9uiAoZVBsNOjvNKB66Oyrvtit74kC7ow=
-github.com/hashicorp/terraform-plugin-go v0.25.0 h1:oi13cx7xXA6QciMcpcFi/rwA974rdTxjqEhXJjbAyks=
-github.com/hashicorp/terraform-plugin-go v0.25.0/go.mod h1:+SYagMYadJP86Kvn+TGeV+ofr/R3g4/If0O5sO96MVw=
+github.com/hashicorp/terraform-plugin-go v0.26.0 h1:cuIzCv4qwigug3OS7iKhpGAbZTiypAfFQmw8aE65O2M=
+github.com/hashicorp/terraform-plugin-go v0.26.0/go.mod h1:+CXjuLDiFgqR+GcrM5a2E2Kal5t5q2jb0E3D57tTdNY=
 github.com/hashicorp/terraform-plugin-log v0.9.0 h1:i7hOA+vdAItN1/7UrfBqBwvYPQ9TFvymaRGZED3FCV0=
 github.com/hashicorp/terraform-plugin-log v0.9.0/go.mod h1:rKL8egZQ/eXSyDqzLUuwUYLVdlYeamldAHSxjUFADow=
-github.com/hashicorp/terraform-registry-address v0.2.3 h1:2TAiKJ1A3MAkZlH1YI/aTVcLZRu7JseiXNRHbOAyoTI=
-github.com/hashicorp/terraform-registry-address v0.2.3/go.mod h1:lFHA76T8jfQteVfT7caREqguFrW3c4MFSPhZB7HHgUM=
+github.com/hashicorp/terraform-registry-address v0.2.4 h1:JXu/zHB2Ymg/TGVCRu10XqNa4Sh2bWcqCNyKWjnCPJA=
+github.com/hashicorp/terraform-registry-address v0.2.4/go.mod h1:tUNYTVyCtU4OIGXXMDp7WNcJ+0W1B4nmstVDgHMjfAU=
 github.com/hashicorp/terraform-svchost v0.1.1 h1:EZZimZ1GxdqFRinZ1tpJwVxxt49xc/S52uzrw4x0jKQ=
 github.com/hashicorp/terraform-svchost v0.1.1/go.mod h1:mNsjQfZyf/Jhz35v6/0LWcv26+X7JPS+buii2c9/ctc=
 github.com/hashicorp/yamux v0.1.1 h1:yrQxtgseBDrq9Y652vSRDvsKCJKOUD+GzTS4Y0Y8pvE=
@@ -142,6 +148,16 @@ github.com/zclconf/go-cty v1.16.1 h1:a5TZEPzBFFR53udlIKApXzj8JIF4ZNQ6abH79z5R1S0
 github.com/zclconf/go-cty v1.16.1/go.mod h1:VvMs5i0vgZdhYawQNq5kePSpLAoz8u1xvZgrPIxfnZE=
 github.com/zclconf/go-cty-debug v0.0.0-20240509010212-0d6042c53940 h1:4r45xpDWB6ZMSMNJFMOjqrGHynW3DIBuR2H9j0ug+Mo=
 github.com/zclconf/go-cty-debug v0.0.0-20240509010212-0d6042c53940/go.mod h1:CmBdvvj3nqzfzJ6nTCIwDTPZ56aVGvDrmztiO5g3qrM=
+go.opentelemetry.io/otel v1.31.0 h1:NsJcKPIW0D0H3NgzPDHmo0WW6SptzPdqg/L1zsIm2hY=
+go.opentelemetry.io/otel v1.31.0/go.mod h1:O0C14Yl9FgkjqcCZAsE053C13OaddMYr/hz6clDkEJE=
+go.opentelemetry.io/otel/metric v1.31.0 h1:FSErL0ATQAmYHUIzSezZibnyVlft1ybhy4ozRPcF2fE=
+go.opentelemetry.io/otel/metric v1.31.0/go.mod h1:C3dEloVbLuYoX41KpmAhOqNriGbA+qqH6PQ5E5mUfnY=
+go.opentelemetry.io/otel/sdk v1.31.0 h1:xLY3abVHYZ5HSfOg3l2E5LUj2Cwva5Y7yGxnSW9H5Gk=
+go.opentelemetry.io/otel/sdk v1.31.0/go.mod h1:TfRbMdhvxIIr/B2N2LQW2S5v9m3gOQ/08KsbbO5BPT0=
+go.opentelemetry.io/otel/sdk/metric v1.31.0 h1:i9hxxLJF/9kkvfHppyLL55aW7iIJz4JjxTeYusH7zMc=
+go.opentelemetry.io/otel/sdk/metric v1.31.0/go.mod h1:CRInTMVvNhUKgSAMbKyTMxqOBC0zgyxzW55lZzX43Y8=
+go.opentelemetry.io/otel/trace v1.31.0 h1:ffjsj1aRouKewfr85U2aGagJ46+MvodynlQ1HYdmJys=
+go.opentelemetry.io/otel/trace v1.31.0/go.mod h1:TXZkRk7SM2ZQLtR6eoAWQFIHPvzQ06FJAsO1tJg480A=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.32.0 h1:euUpcYgM8WcP71gNpTqQCn6rC2t6ULUPiOzfWaXVVfc=
@@ -153,8 +169,8 @@ golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
-golang.org/x/net v0.33.0 h1:74SYHlV8BIgHIFC/LrYkOGIwL19eTYXQ5wc6TBuO36I=
-golang.org/x/net v0.33.0/go.mod h1:HXLR5J+9DxmrqMwG9qjGCxZ+zKXxBru04zlTvWlWuN4=
+golang.org/x/net v0.34.0 h1:Mb7Mrk043xzHgnRM88suvJFwzVrRfHEHJEl5/71CKw0=
+golang.org/x/net v0.34.0/go.mod h1:di0qlW3YNM5oh6GqDGQr92MyTozJPmybPK4Ev/Gm31k=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -195,14 +211,14 @@ golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8T
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
 google.golang.org/appengine v1.6.8 h1:IhEN5q69dyKagZPYMSdIjS2HqprW324FRQZJcGqPAsM=
 google.golang.org/appengine v1.6.8/go.mod h1:1jJ3jBArFh5pcgW8gCtRJnepW8FzD1V44FJffLiz/Ds=
-google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 h1:e7S5W7MGGLaSu8j3YjdezkZ+m1/Nm0uRVRMEMGk26Xs=
-google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142/go.mod h1:UqMtugtsSgubUsoxbuAoiCXvqvErP7Gf0so0mK9tHxU=
-google.golang.org/grpc v1.67.1 h1:zWnc1Vrcno+lHZCOofnIMvycFcc0QRGIzm9dhnDX68E=
-google.golang.org/grpc v1.67.1/go.mod h1:1gLDyUQU7CTLJI90u3nXZ9ekeghjeM7pTDZlqFNg2AA=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20241015192408-796eee8c2d53 h1:X58yt85/IXCx0Y3ZwN6sEIKZzQtDEYaBWrDvErdXrRE=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20241015192408-796eee8c2d53/go.mod h1:GX3210XPVPUjJbTUbvwI8f2IpZDMZuPJWDzDuebbviI=
+google.golang.org/grpc v1.69.4 h1:MF5TftSMkd8GLw/m0KM6V8CMOCY6NZ1NQDPGFgbTt4A=
+google.golang.org/grpc v1.69.4/go.mod h1:vyjdE6jLBI76dgpDojsFGNaHlxdjXN9ghpnd2o7JGZ4=
 google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
 google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
-google.golang.org/protobuf v1.35.1 h1:m3LfL6/Ca+fqnjnlqQXNpFPABW1UD7mjh8KO2mKFytA=
-google.golang.org/protobuf v1.35.1/go.mod h1:9fA7Ob0pmnwhb644+1+CVWFRbNajQ6iRojtC/QF5bRE=
+google.golang.org/protobuf v1.36.3 h1:82DV7MYdb8anAVi3qge1wSnMDrnKK7ebr+I0hHRN1BU=
+google.golang.org/protobuf v1.36.3/go.mod h1:9fA7Ob0pmnwhb644+1+CVWFRbNajQ6iRojtC/QF5bRE=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

helper/schema/core_schema.go

@@ -167,6 +167,7 @@ func (s *Schema) coreConfigSchemaAttribute() *configschema.Attribute {
 		Description:     desc,
 		DescriptionKind: descKind,
 		Deprecated:      s.Deprecated != "",
+		WriteOnly:       s.WriteOnly,
 	}
 }
 

helper/schema/core_schema_test.go

@@ -458,6 +458,25 @@ func TestSchemaMapCoreConfigSchema(t *testing.T) {
 				BlockTypes: map[string]*configschema.NestedBlock{},
 			}),
 		},
+		"write-only": {
+			map[string]*Schema{
+				"string": {
+					Type:      TypeString,
+					Optional:  true,
+					WriteOnly: true,
+				},
+			},
+			testResource(&configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"string": {
+						Type:      cty.String,
+						Optional:  true,
+						WriteOnly: true,
+					},
+				},
+				BlockTypes: map[string]*configschema.NestedBlock{},
+			}),
+		},
 	}
 
 	for name, test := range tests {

helper/schema/grpc_provider.go

@@ -283,6 +283,32 @@ func (s *GRPCProviderServer) ValidateResourceTypeConfig(ctx context.Context, req
 		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)
 		return resp, nil
 	}
+	if req.ClientCapabilities == nil || !req.ClientCapabilities.WriteOnlyAttributesAllowed {
+		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, validateWriteOnlyNullValues(configVal, schemaBlock, cty.Path{}))
+	}
+
+	r := s.provider.ResourcesMap[req.TypeName]
+
+	// Calling all ValidateRawResourceConfigFunc here since they validate on the raw go-cty config value
+	// and were introduced after the public provider.ValidateResource method.
+	if r.ValidateRawResourceConfigFuncs != nil {
+		writeOnlyAllowed := false
+
+		if req.ClientCapabilities != nil {
+			writeOnlyAllowed = req.ClientCapabilities.WriteOnlyAttributesAllowed
+		}
+
+		validateReq := ValidateResourceConfigFuncRequest{
+			WriteOnlyAttributesAllowed: writeOnlyAllowed,
+			RawConfig:                  configVal,
+		}
+
+		for _, validateFunc := range r.ValidateRawResourceConfigFuncs {
+			validateResp := &ValidateResourceConfigFuncResponse{}
+			validateFunc(ctx, validateReq, validateResp)
+			resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, validateResp.Diagnostics)
+		}
+	}
 
 	config := terraform.NewResourceConfigShimmed(configVal, schemaBlock)
 
@@ -394,6 +420,9 @@ func (s *GRPCProviderServer) UpgradeResourceState(ctx context.Context, req *tfpr
 	// Normalize the value and fill in any missing blocks.
 	val = objchange.NormalizeObjectFromLegacySDK(val, schemaBlock)
 
+	// Set any write-only attribute values to null
+	val = setWriteOnlyNullValues(val, schemaBlock)
+
 	// encode the final state to the expected msgpack format
 	newStateMP, err := msgpack.Marshal(val, schemaBlock.ImpliedType())
 	if err != nil {
@@ -738,6 +767,7 @@ func (s *GRPCProviderServer) ReadResource(ctx context.Context, req *tfprotov5.Re
 
 	newStateVal = normalizeNullValues(newStateVal, stateVal, false)
 	newStateVal = copyTimeoutValues(newStateVal, stateVal)
+	newStateVal = setWriteOnlyNullValues(newStateVal, schemaBlock)
 
 	newStateMP, err := msgpack.Marshal(newStateVal, schemaBlock.ImpliedType())
 	if err != nil {
@@ -937,6 +967,9 @@ func (s *GRPCProviderServer) PlanResourceChange(ctx context.Context, req *tfprot
 		plannedStateVal = SetUnknowns(plannedStateVal, schemaBlock)
 	}
 
+	// Set any write-only attribute values to null
+	plannedStateVal = setWriteOnlyNullValues(plannedStateVal, schemaBlock)
+
 	plannedMP, err := msgpack.Marshal(plannedStateVal, schemaBlock.ImpliedType())
 	if err != nil {
 		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)
@@ -1184,6 +1217,8 @@ func (s *GRPCProviderServer) ApplyResourceChange(ctx context.Context, req *tfpro
 
 	newStateVal = copyTimeoutValues(newStateVal, plannedStateVal)
 
+	newStateVal = setWriteOnlyNullValues(newStateVal, schemaBlock)
+
 	newStateMP, err := msgpack.Marshal(newStateVal, schemaBlock.ImpliedType())
 	if err != nil {
 		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)
@@ -1305,6 +1340,9 @@ func (s *GRPCProviderServer) ImportResourceState(ctx context.Context, req *tfpro
 			newStateVal = cty.ObjectVal(newStateValueMap)
 		}
 
+		// Set any write-only attribute values to null
+		newStateVal = setWriteOnlyNullValues(newStateVal, schemaBlock)
+
 		newStateMP, err := msgpack.Marshal(newStateVal, schemaBlock.ImpliedType())
 		if err != nil {
 			resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)