reference: Update type matching to align w/ Terraform's (#243)

Terraform itself basically doesn't use cty's TestConformance, but instead uses the convert.Convert function.
This makes the type comparison a lot more lenient, where it accepts basically any primitive type for any other.
It does however reject mismatch between complex types.

Other products / language servers may benefit from the stricter comparison (as implemented by TestConformance)
but we do not have enough data to understand this problem space and so we optimise for Terraform for now.
This should not hurt other products unless they have a lot of references to filter. At worst they'll get
*more* completion items and hover/semtokens for references which are not relevant, but should still get
the ones which are relevant.

decoder/expr_reference_completion_test.go

@@ -48,6 +48,13 @@ func TestCompletionAtPos_exprReference(t *testing.T) {
 						lang.RootStep{Name: "local"},
 						lang.AttrStep{Name: "bar"},
 					},
+					Type: cty.List(cty.Number),
+				},
+				{
+					Addr: lang.Address{
+						lang.RootStep{Name: "local"},
+						lang.AttrStep{Name: "baz"},
+					},
 					Type: cty.Number,
 				},
 			},
@@ -68,6 +75,20 @@ func TestCompletionAtPos_exprReference(t *testing.T) {
 						},
 					},
 				},
+				{
+					Label:  "local.baz",
+					Detail: "number",
+					Kind:   lang.TraversalCandidateKind,
+					TextEdit: lang.TextEdit{
+						NewText: "local.baz",
+						Snippet: "local.baz",
+						Range: hcl.Range{
+							Filename: "test.tf",
+							Start:    hcl.Pos{Line: 1, Column: 8, Byte: 7},
+							End:      hcl.Pos{Line: 1, Column: 8, Byte: 7},
+						},
+					},
+				},
 			}),
 		},
 		{
@@ -85,7 +106,7 @@ func TestCompletionAtPos_exprReference(t *testing.T) {
 						lang.RootStep{Name: "local"},
 						lang.AttrStep{Name: "foo"},
 					},
-					Type: cty.String,
+					Type: cty.List(cty.String),
 				},
 				{
 					Addr: lang.Address{
@@ -143,7 +164,7 @@ func TestCompletionAtPos_exprReference(t *testing.T) {
 						lang.RootStep{Name: "local"},
 						lang.AttrStep{Name: "bar"},
 					},
-					Type: cty.Number,
+					Type: cty.List(cty.Number),
 				},
 				{
 					Addr: lang.Address{
@@ -194,7 +215,7 @@ func TestCompletionAtPos_exprReference(t *testing.T) {
 						lang.RootStep{Name: "local"},
 						lang.AttrStep{Name: "bar"},
 					},
-					Type: cty.Number,
+					Type: cty.List(cty.Number),
 				},
 				{
 					Addr: lang.Address{

decoder/expression_candidates_legacy_test.go

@@ -1478,7 +1478,7 @@ func TestLegacyDecoder_CandidateAtPos_traversalExpressions(t *testing.T) {
 				Attributes: map[string]*schema.AttributeSchema{
 					"attr": {
 						Expr: schema.ExprConstraints{
-							schema.TraversalExpr{OfType: cty.String},
+							schema.TraversalExpr{OfType: cty.List(cty.String)},
 						},
 					},
 				},
@@ -1521,7 +1521,7 @@ func TestLegacyDecoder_CandidateAtPos_traversalExpressions(t *testing.T) {
 						lang.RootStep{Name: "var"},
 						lang.AttrStep{Name: "first"},
 					},
-					Type: cty.Bool,
+					Type: cty.List(cty.Number),
 				},
 				reference.Target{
 					Addr: lang.Address{

decoder/hover_expressions_legacy_test.go

@@ -1410,7 +1410,7 @@ func TestLegacyDecoder_HoverAtPos_traversalExpressions(t *testing.T) {
 						lang.RootStep{Name: "var"},
 						lang.AttrStep{Name: "blah"},
 					},
-					Type: cty.Bool,
+					Type: cty.List(cty.Bool),
 				},
 			},
 			reference.Origins{

decoder/semantic_tokens_expr_legacy_test.go

@@ -1481,7 +1481,7 @@ func TestLegacyDecoder_SemanticTokensInFile_traversalExpression(t *testing.T) {
 						lang.RootStep{Name: "var"},
 						lang.AttrStep{Name: "blah"},
 					},
-					Type: cty.Bool,
+					Type: cty.List(cty.Bool),
 				},
 			},
 			reference.Origins{

reference/target.go

@@ -10,6 +10,7 @@ import (
 	"github.com/hashicorp/hcl-lang/schema"
 	"github.com/hashicorp/hcl/v2"
 	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/convert"
 )
 
 type Target struct {
@@ -141,30 +142,30 @@ func (r Target) TargetRange() (hcl.Range, bool) {
 }
 
 func (target Target) MatchesConstraint(ref schema.Reference) bool {
-	return target.MatchesScopeId(ref.OfScopeId) && target.ConformsToType(ref.OfType)
+	return target.MatchesScopeId(ref.OfScopeId) && target.IsConvertibleToType(ref.OfType)
 }
 
 func (ref Target) LegacyMatchesConstraint(te schema.TraversalExpr) bool {
-	return ref.MatchesScopeId(te.OfScopeId) && ref.ConformsToType(te.OfType)
+	return ref.MatchesScopeId(te.OfScopeId) && ref.IsConvertibleToType(te.OfType)
 }
 
 func (ref Target) MatchesScopeId(scopeId lang.ScopeId) bool {
 	return scopeId == "" || ref.ScopeId == scopeId
 }
 
-func (ref Target) ConformsToType(typ cty.Type) bool {
-	conformsToType := false
+func (ref Target) IsConvertibleToType(typ cty.Type) bool {
+	isConvertible := false
 	if typ != cty.NilType && ref.Type != cty.NilType {
 		if ref.Type == cty.DynamicPseudoType {
-			// anything conforms with dynamic
-			conformsToType = true
+			// anything is convertible to dynamic
+			isConvertible = true
 		}
-		if errs := ref.Type.TestConformance(typ); len(errs) == 0 {
-			conformsToType = true
+		if _, err := convert.Convert(cty.UnknownVal(ref.Type), typ); err == nil {
+			isConvertible = true
 		}
 	}
 
-	return conformsToType || (typ == cty.NilType && ref.Type == cty.NilType)
+	return isConvertible || (typ == cty.NilType && ref.Type == cty.NilType)
 }
 
 func (target Target) Matches(origin MatchableOrigin) bool {
@@ -202,7 +203,7 @@ func (target Target) Matches(origin MatchableOrigin) bool {
 			matchesCons = true
 			continue
 		}
-		if cons.OfType != cty.NilType && target.ConformsToType(cons.OfType) {
+		if cons.OfType != cty.NilType && target.IsConvertibleToType(cons.OfType) {
 			matchesCons = true
 		}
 		if cons.OfType == cty.NilType && target.Type == cty.NilType {

reference/targets_test.go

@@ -738,6 +738,13 @@ func TestTargets_LegacyMatchWalk(t *testing.T) {
 					},
 					Type: cty.String,
 				},
+				Target{
+					Addr: lang.Address{
+						lang.RootStep{Name: "var"},
+						lang.AttrStep{Name: "another"},
+					},
+					Type: cty.List(cty.String),
+				},
 			},
 			schema.TraversalExpr{
 				OfType: cty.String,
@@ -754,6 +761,13 @@ func TestTargets_LegacyMatchWalk(t *testing.T) {
 				End:      hcl.InitialPos,
 			},
 			Targets{
+				Target{
+					Addr: lang.Address{
+						lang.RootStep{Name: "var"},
+						lang.AttrStep{Name: "first"},
+					},
+					Type: cty.Bool,
+				},
 				Target{
 					Addr: lang.Address{
 						lang.RootStep{Name: "var"},