Update go-cty and improve documentation for optional and default attributes

6 files changed, 60 insertions, 36 deletions

diff --git a/ext/typeexpr/README.md b/ext/typeexpr/README.md
index 058f1e3..c0fa6ab 100644
--- a/ext/typeexpr/README.md
+++ b/ext/typeexpr/README.md
@@ -66,6 +66,27 @@ types with weird attributes generally show up only from arbitrary object
 constructors in configuration files, which are usually treated either as maps
 or as the dynamic pseudo-type.
 
+### Optional Object Attributes
+
+As part of object expressions attributes can be marked as optional. Missing 
+object attributes would typically result in an error when type constraints are
+validated or used. Optional missing attributes, however, would not result in an 
+error. The `cty` ["convert" function](#the-convert-cty-function) will populate 
+missing optional attributes with null values.
+
+For example:
+
+* `object({name=string,age=optional(number)})`
+
+Optional attributes can also be specified with default values. The 
+`TypeConstraintWithDefaults` function will return a `Defaults` object that can
+be used to populate missing optional attributes with defaults in a given 
+`cty.Value`.
+
+For example:
+
+* `object({name=string,age=optional(number, 0)})`
+
 ## Type Constraints as Values
 
 Along with defining a convention for writing down types using HCL expression
diff --git a/ext/typeexpr/defaults.go b/ext/typeexpr/defaults.go
index 851c72f..4e96057 100644
--- a/ext/typeexpr/defaults.go
+++ b/ext/typeexpr/defaults.go
@@ -6,7 +6,7 @@ import (
 
 // Defaults represents a type tree which may contain default values for
 // optional object attributes at any level. This is used to apply nested
-// defaults to an input value before converting it to the concrete type.
+// defaults to a given cty.Value.
 type Defaults struct {
 	// Type of the node for which these defaults apply. This is necessary in
 	// order to determine how to inspect the Defaults and Children collections.
@@ -28,8 +28,8 @@ type Defaults struct {
 
 // Apply walks the given value, applying specified defaults wherever optional
 // attributes are missing. The input and output values may have different
-// types, and the result may still require type conversion to the final desired
-// type.
+// types, to avoid this the input value should be converted into the desired
+// type first.
 //
 // This function is permissive and does not report errors, assuming that the
 // caller will have better context to report useful type conversion failure
diff --git a/ext/typeexpr/public.go b/ext/typeexpr/public.go
index 82f215c..f2e187e 100644
--- a/ext/typeexpr/public.go
+++ b/ext/typeexpr/public.go
@@ -35,10 +35,6 @@ func TypeConstraint(expr hcl.Expression) (cty.Type, hcl.Diagnostics) {
 // constraint which may include default values for object attributes. If
 // successful both the resulting type and corresponding defaults are returned.
 // If unsuccessful, error diagnostics are returned.
-//
-// When using this function, defaults should be applied to the input value
-// before type conversion, to ensure that objects with missing attributes have
-// default values populated.
 func TypeConstraintWithDefaults(expr hcl.Expression) (cty.Type, *Defaults, hcl.Diagnostics) {
 	return getType(expr, true, true)
 }
diff --git a/go.mod b/go.mod
index 8f7c79f..0d22ec3 100644
--- a/go.mod
+++ b/go.mod
@@ -14,7 +14,7 @@ require (
 	github.com/mitchellh/go-wordwrap v0.0.0-20150314170334-ad45545899c7
 	github.com/sergi/go-diff v1.0.0
 	github.com/spf13/pflag v1.0.2
-	github.com/zclconf/go-cty v1.8.0
+	github.com/zclconf/go-cty v1.12.0
 	github.com/zclconf/go-cty-debug v0.0.0-20191215020915-b22d67c1ba0b
 	golang.org/x/crypto v0.0.0-20220517005047-85d78b3ac167
 )
@@ -25,5 +25,5 @@ require (
 	github.com/stretchr/testify v1.2.2 // indirect
 	golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1 // indirect
 	golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1 // indirect
-	golang.org/x/text v0.3.6 // indirect
+	golang.org/x/text v0.3.7 // indirect
 )
diff --git a/go.sum b/go.sum
index 2d2ddb3..ac1a714 100644
--- a/go.sum
+++ b/go.sum
@@ -2,7 +2,6 @@ github.com/agext/levenshtein v1.2.1 h1:QmvMAjj2aEICytGiWzmxoE0x2KZvE0fvmqMOfy2tj
 github.com/agext/levenshtein v1.2.1/go.mod h1:JEDfjyjHDjOF/1e4FlBE/PkbqA9OfWu2ki2W0IB5558=
 github.com/apparentlymart/go-dump v0.0.0-20180507223929-23540a00eaa3 h1:ZSTrOEhiM5J5RFxEaFvMZVEAM1KvT1YzbEOwB2EAGjA=
 github.com/apparentlymart/go-dump v0.0.0-20180507223929-23540a00eaa3/go.mod h1:oL81AME2rN47vu18xqj1S1jPIPuN7afo62yKTNn3XMM=
-github.com/apparentlymart/go-textseg v1.0.0 h1:rRmlIsPEEhUTIKQb7T++Nz/A5Q6C9IuX2wFoYVvnCs0=
 github.com/apparentlymart/go-textseg v1.0.0/go.mod h1:z96Txxhf3xSFMPmb5X/1W05FF/Nj9VFpLOpjS5yuumk=
 github.com/apparentlymart/go-textseg/v13 v13.0.0 h1:Y+KvPE1NYz0xl601PVImeQfFyEy6iT90AvPUL1NNfNw=
 github.com/apparentlymart/go-textseg/v13 v13.0.0/go.mod h1:ZK2fH7c4NqDTLtiYLvIkEghdlcqw7yxLeM89kiTRPUo=
@@ -11,8 +10,6 @@ github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 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/protobuf v1.1.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/golang/protobuf v1.3.4/go.mod h1:vzj43D7+SQXF/4pzW/hwtAqwc6iTitCiVSaWz5lYuqw=
 github.com/google/go-cmp v0.3.1 h1:Xye71clBPdm5HgqGwUkwhbynsUJZhDbS20FvLhQ2izg=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
@@ -33,34 +30,22 @@ github.com/spf13/pflag v1.0.2/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnIn
 github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/vmihailenco/msgpack v3.3.3+incompatible/go.mod h1:fy3FlTQTDXWkZ7Bh6AcGMlsjHatGryHQYUTf1ShIgkk=
-github.com/vmihailenco/msgpack/v4 v4.3.12/go.mod h1:gborTTJjAo/GWTqqRjrLCn9pgNN+NXzzngzBKDPIqw4=
-github.com/vmihailenco/tagparser v0.1.1/go.mod h1:OeAg3pn3UbLjkWt+rN9oFYB6u/cQgqMEUPoW2WPyhdI=
 github.com/zclconf/go-cty v1.2.0/go.mod h1:hOPWgoHbaTUnI5k4D2ld+GRpFJSCe6bCM7m1q/N4PQ8=
-github.com/zclconf/go-cty v1.8.0 h1:s4AvqaeQzJIu3ndv4gVIhplVD0krU+bgrcLSVUnaWuA=
-github.com/zclconf/go-cty v1.8.0/go.mod h1:vVKLxnk3puL4qRAv72AO+W99LUD4da90g3uUAzyuvAk=
+github.com/zclconf/go-cty v1.12.0 h1:F5E/vbilcrCtat9sYcEjlwwg1mDqbRTjyXR57nnx5sc=
+github.com/zclconf/go-cty v1.12.0/go.mod h1:s9IfD1LK5ccNMSWCVFCE2rJfHiZgi7JijgeWIMfhLvA=
 github.com/zclconf/go-cty-debug v0.0.0-20191215020915-b22d67c1ba0b h1:FosyBZYxY34Wul7O/MSKey3txpPYyCqVO5ZyceuQJEI=
 github.com/zclconf/go-cty-debug v0.0.0-20191215020915-b22d67c1ba0b/go.mod h1:ZRKQfBXbGkpdV6QMzT3rU1kSTAnfu1dO8dPKjYprgj8=
-golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20220517005047-85d78b3ac167 h1:O8uGbHCqlTp2P6QJSLmCojM4mN6UemYv8K+dCnmHmu0=
 golang.org/x/crypto v0.0.0-20220517005047-85d78b3ac167/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/net v0.0.0-20180811021610-c39426892332/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
-golang.org/x/net v0.0.0-20190603091049-60506f45cf65/go.mod h1:HSz+uSET+XFnRR8LxR5pz3Of3rY3CfYBVs4xY44aLks=
-golang.org/x/net v0.0.0-20200301022130-244492dfa37a/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
-golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1 h1:SrN+KX8Art/Sf4HNj6Zcz06G7VEz+7w9tdXTPOZ7+l4=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1 h1:v+OssWQX+hTHEmOBgwxdZxK4zHq3yOs8F9J7mk0PY8E=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
-golang.org/x/text v0.3.5/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.3.6 h1:aRYxNxv6iGQlyVaZmk6ZgYEDa+Jg18DxebPSrd6bg1M=
-golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
-google.golang.org/appengine v1.6.5/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/hclsyntax/expression_test.go b/hclsyntax/expression_test.go
index 77d959f..d22406f 100644
--- a/hclsyntax/expression_test.go
+++ b/hclsyntax/expression_test.go
@@ -1847,6 +1847,28 @@ EOT
 			cty.NumberIntVal(1),
 			0,
 		},
+		{ // auto-converts collection types
+			`true ? listOf1Tuple : listOf0Tuple`,
+			&hcl.EvalContext{
+				Variables: map[string]cty.Value{
+					"listOf1Tuple": cty.ListVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True})}),
+					"listOf0Tuple": cty.ListVal([]cty.Value{cty.EmptyTupleVal}),
+				},
+			},
+			cty.ListVal([]cty.Value{cty.ListVal([]cty.Value{cty.True})}),
+			0,
+		},
+		{
+			`true ? setOf1Tuple : setOf0Tuple`,
+			&hcl.EvalContext{
+				Variables: map[string]cty.Value{
+					"setOf1Tuple": cty.SetVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True})}),
+					"setOf0Tuple": cty.SetVal([]cty.Value{cty.EmptyTupleVal}),
+				},
+			},
+			cty.SetVal([]cty.Value{cty.ListVal([]cty.Value{cty.True})}),
+			0,
+		},
 		{ // marked argument expansion
 			`min(xs...)`,
 			&hcl.EvalContext{
@@ -1937,26 +1959,26 @@ func TestExpressionErrorMessages(t *testing.T) {
 			"The true and false result expressions must have consistent types. The 'false' value includes object attribute \"b\", which is absent in the 'true' value.",
 		},
 		{
-			"true ? listOf1Tuple : listOf0Tuple",
+			"true ? listOf2Tuple : listOf1Tuple",
 			&hcl.EvalContext{
 				Variables: map[string]cty.Value{
+					"listOf2Tuple": cty.ListVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True, cty.Zero})}),
 					"listOf1Tuple": cty.ListVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True})}),
-					"listOf0Tuple": cty.ListVal([]cty.Value{cty.EmptyTupleVal}),
 				},
 			},
 			"Inconsistent conditional result types",
-			"The true and false result expressions must have consistent types. Mismatched list element types: The 'true' tuple has length 1, but the 'false' tuple has length 0.",
+			"The true and false result expressions must have consistent types. Mismatched list element types: The 'true' tuple has length 2, but the 'false' tuple has length 1.",
 		},
 		{
-			"true ? setOf1Tuple : setOf0Tuple",
+			"true ? setOf2Tuple : setOf1Tuple",
 			&hcl.EvalContext{
 				Variables: map[string]cty.Value{
+					"setOf2Tuple": cty.SetVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True, cty.Zero})}),
 					"setOf1Tuple": cty.SetVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True})}),
-					"setOf0Tuple": cty.SetVal([]cty.Value{cty.EmptyTupleVal}),
 				},
 			},
 			"Inconsistent conditional result types",
-			"The true and false result expressions must have consistent types. Mismatched set element types: The 'true' tuple has length 1, but the 'false' tuple has length 0.",
+			"The true and false result expressions must have consistent types. Mismatched set element types: The 'true' tuple has length 2, but the 'false' tuple has length 1.",
 		},
 		{
 			"true ? mapOf1Tuple : mapOf2Tuple",
@@ -1970,11 +1992,11 @@ func TestExpressionErrorMessages(t *testing.T) {
 			"The true and false result expressions must have consistent types. Mismatched map element types: The 'true' tuple has length 1, but the 'false' tuple has length 2.",
 		},
 		{
-			"true ? listOfListOf1Tuple : listOfListOf0Tuple",
+			"true ? listOfListOf2Tuple : listOfListOf1Tuple",
 			&hcl.EvalContext{
 				Variables: map[string]cty.Value{
+					"listOfListOf2Tuple": cty.ListVal([]cty.Value{cty.ListVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True, cty.Zero})})}),
 					"listOfListOf1Tuple": cty.ListVal([]cty.Value{cty.ListVal([]cty.Value{cty.TupleVal([]cty.Value{cty.True})})}),
-					"listOfListOf0Tuple": cty.ListVal([]cty.Value{cty.ListVal([]cty.Value{cty.EmptyTupleVal})}),
 				},
 			},
 			"Inconsistent conditional result types",