schema: Introduce BuiltinReferences(modPath) (#93)

* schema: Introduce BuiltinReferences(modPath)

* add comment

internal/schema/refscope/scopes.go

@@ -5,6 +5,7 @@ import (
 )
 
 var (
+	BuiltinScope  = lang.ScopeId("builtin")
 	DataScope     = lang.ScopeId("data")
 	LocalScope    = lang.ScopeId("local")
 	ModuleScope   = lang.ScopeId("module")

schema/builtin_references.go

@@ -0,0 +1,55 @@
+package schema
+
+import (
+	"github.com/hashicorp/hcl-lang/lang"
+	"github.com/hashicorp/hcl-lang/reference"
+	"github.com/hashicorp/terraform-schema/internal/schema/refscope"
+	"github.com/zclconf/go-cty/cty"
+)
+
+// BuiltinReferences returns known "built-in" reference targets
+// (range-less references available within any module)
+func BuiltinReferences(modPath string) reference.Targets {
+	return reference.Targets{
+		{
+			Addr: lang.Address{
+				lang.RootStep{Name: "path"},
+				lang.AttrStep{Name: "module"},
+			},
+			ScopeId: refscope.BuiltinScope,
+			Type:    cty.String,
+			Description: lang.Markdown("The filesystem path of the module where the expression is placed\n\n" +
+				modPath),
+		},
+		{
+			Addr: lang.Address{
+				lang.RootStep{Name: "path"},
+				lang.AttrStep{Name: "root"},
+			},
+			ScopeId:     refscope.BuiltinScope,
+			Type:        cty.String,
+			Description: lang.Markdown("The filesystem path of the root module of the configuration"),
+		},
+		{
+			Addr: lang.Address{
+				lang.RootStep{Name: "path"},
+				lang.AttrStep{Name: "cwd"},
+			},
+			ScopeId: refscope.BuiltinScope,
+			Type:    cty.String,
+			Description: lang.Markdown("The filesystem path of the current working directory.\n\n" +
+				"In normal use of Terraform this is the same as `path.root`, " +
+				"but some advanced uses of Terraform run it from a directory " +
+				"other than the root module directory, causing these paths to be different."),
+		},
+		{
+			Addr: lang.Address{
+				lang.RootStep{Name: "terraform"},
+				lang.AttrStep{Name: "workspace"},
+			},
+			ScopeId:     refscope.BuiltinScope,
+			Type:        cty.String,
+			Description: lang.Markdown("The name of the currently selected workspace"),
+		},
+	}
+}