lang/funcs: add (console-only) TypeFunction

command/console.go

@@ -127,6 +127,10 @@ func (c *ConsoleCommand) Run(args []string) int {
 		c.showDiagnostics(diags)
 		return 1
 	}
+
+	// set the ConsoleMode to true so any available console-only functions included.
+	scope.ConsoleMode = true
+
 	if diags.HasErrors() {
 		diags = diags.Append(tfdiags.SimpleWarning("Due to the problems above, some expressions may produce unexpected results."))
 	}

go.sum

@@ -595,8 +595,6 @@ github.com/zclconf/go-cty v1.0.0/go.mod h1:xnAOWiHeOqg2nWS62VtQ7pbOu17FtxJNW8RLE
 github.com/zclconf/go-cty v1.1.0/go.mod h1:xnAOWiHeOqg2nWS62VtQ7pbOu17FtxJNW8RLEih+O3s=
 github.com/zclconf/go-cty v1.2.0/go.mod h1:hOPWgoHbaTUnI5k4D2ld+GRpFJSCe6bCM7m1q/N4PQ8=
 github.com/zclconf/go-cty v1.8.0/go.mod h1:vVKLxnk3puL4qRAv72AO+W99LUD4da90g3uUAzyuvAk=
-github.com/zclconf/go-cty v1.8.1 h1:SI0LqNeNxAgv2WWqWJMlG2/Ad/6aYJ7IVYYMigmfkuI=
-github.com/zclconf/go-cty v1.8.1/go.mod h1:vVKLxnk3puL4qRAv72AO+W99LUD4da90g3uUAzyuvAk=
 github.com/zclconf/go-cty v1.8.2 h1:u+xZfBKgpycDnTNjPhGiTEYZS5qS/Sb5MqSfm7vzcjg=
 github.com/zclconf/go-cty v1.8.2/go.mod h1:vVKLxnk3puL4qRAv72AO+W99LUD4da90g3uUAzyuvAk=
 github.com/zclconf/go-cty-debug v0.0.0-20191215020915-b22d67c1ba0b h1:FosyBZYxY34Wul7O/MSKey3txpPYyCqVO5ZyceuQJEI=

lang/funcs/conversion.go

@@ -1,7 +1,10 @@
 package funcs
 
 import (
+	"fmt"
+	"sort"
 	"strconv"
+	"strings"
 
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/convert"
@@ -91,3 +94,128 @@ func MakeToFunc(wantTy cty.Type) function.Function {
 		},
 	})
 }
+
+var TypeFunc = function.New(&function.Spec{
+	Params: []function.Parameter{
+		{
+			Name:             "value",
+			Type:             cty.DynamicPseudoType,
+			AllowDynamicType: true,
+			AllowUnknown:     true,
+			AllowNull:        true,
+		},
+	},
+	Type: function.StaticReturnType(cty.String),
+	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
+		return cty.StringVal(TypeString(args[0].Type())).Mark("raw"), nil
+	},
+})
+
+// Modified copy of TypeString from go-cty:
+// https://github.com/zclconf/go-cty-debug/blob/master/ctydebug/type_string.go
+//
+// TypeString returns a string representation of a given type that is
+// reminiscent of Go syntax calling into the cty package but is mainly
+// intended for easy human inspection of values in tests, debug output, etc.
+//
+// The resulting string will include newlines and indentation in order to
+// increase the readability of complex structures. It always ends with a
+// newline, so you can print this result directly to your output.
+func TypeString(ty cty.Type) string {
+	var b strings.Builder
+	writeType(ty, &b, 0)
+	return b.String()
+}
+
+func writeType(ty cty.Type, b *strings.Builder, indent int) {
+	switch {
+	case ty == cty.NilType:
+		b.WriteString("nil")
+		return
+	case ty.IsObjectType():
+		atys := ty.AttributeTypes()
+		if len(atys) == 0 {
+			b.WriteString("object({})")
+			return
+		}
+		attrNames := make([]string, 0, len(atys))
+		for name := range atys {
+			attrNames = append(attrNames, name)
+		}
+		sort.Strings(attrNames)
+		b.WriteString("object({\n")
+		indent++
+		for _, name := range attrNames {
+			aty := atys[name]
+			b.WriteString(indentSpaces(indent))
+			fmt.Fprintf(b, "%s: ", name)
+			writeType(aty, b, indent)
+			b.WriteString(",\n")
+		}
+		indent--
+		b.WriteString(indentSpaces(indent))
+		b.WriteString("})")
+	case ty.IsTupleType():
+		etys := ty.TupleElementTypes()
+		if len(etys) == 0 {
+			b.WriteString("tuple([])")
+			return
+		}
+		b.WriteString("tuple([\n")
+		indent++
+		for _, ety := range etys {
+			b.WriteString(indentSpaces(indent))
+			writeType(ety, b, indent)
+			b.WriteString(",\n")
+		}
+		indent--
+		b.WriteString(indentSpaces(indent))
+		b.WriteString("])")
+	case ty.IsCollectionType():
+		ety := ty.ElementType()
+		switch {
+		case ty.IsListType():
+			b.WriteString("list(")
+		case ty.IsMapType():
+			b.WriteString("map(")
+		case ty.IsSetType():
+			b.WriteString("set(")
+		default:
+			// At the time of writing there are no other collection types,
+			// but we'll be robust here and just pass through the GoString
+			// of anything we don't recognize.
+			b.WriteString(ty.FriendlyName())
+			return
+		}
+		// Because object and tuple types render split over multiple
+		// lines, a collection type container around them can end up
+		// being hard to see when scanning, so we'll generate some extra
+		// indentation to make a collection of structural type more visually
+		// distinct from the structural type alone.
+		complexElem := ety.IsObjectType() || ety.IsTupleType()
+		if complexElem {
+			indent++
+			b.WriteString("\n")
+			b.WriteString(indentSpaces(indent))
+		}
+		writeType(ty.ElementType(), b, indent)
+		if complexElem {
+			indent--
+			b.WriteString(",\n")
+			b.WriteString(indentSpaces(indent))
+		}
+		b.WriteString(")")
+	default:
+		// For any other type we'll just use its GoString and assume it'll
+		// follow the usual GoString conventions.
+		b.WriteString(ty.FriendlyName())
+	}
+}
+
+func indentSpaces(level int) string {
+	return strings.Repeat("    ", level)
+}
+
+func Type(input []cty.Value) (cty.Value, error) {
+	return TypeFunc.Call(input)
+}

lang/funcs/conversion_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
 	"github.com/zclconf/go-cty/cty"
 )
 
@@ -177,3 +178,92 @@ func TestTo(t *testing.T) {
 		})
 	}
 }
+
+func TestType(t *testing.T) {
+	tests := []struct {
+		Input cty.Value
+		Want  string
+	}{
+		// Primititves
+		{
+			cty.StringVal("a"),
+			"string",
+		},
+		{
+			cty.NumberIntVal(42),
+			"number",
+		},
+		{
+			cty.BoolVal(true),
+			"bool",
+		},
+		// Collections
+		{
+			cty.EmptyObjectVal,
+			`object({})`,
+		},
+		{
+			cty.EmptyTupleVal,
+			`tuple([])`,
+		},
+		{
+			cty.ListValEmpty(cty.String),
+			`list(string)`,
+		},
+		{
+			cty.MapValEmpty(cty.String),
+			`map(string)`,
+		},
+		{
+			cty.SetValEmpty(cty.String),
+			`set(string)`,
+		},
+		{
+			cty.ListVal([]cty.Value{cty.StringVal("a")}),
+			`list(string)`,
+		},
+		{
+			cty.ListVal([]cty.Value{cty.ListVal([]cty.Value{cty.NumberIntVal(42)})}),
+			`list(list(number))`,
+		},
+		{
+			cty.ListVal([]cty.Value{cty.MapValEmpty(cty.String)}),
+			`list(map(string))`,
+		},
+		{
+			cty.ListVal([]cty.Value{cty.ObjectVal(map[string]cty.Value{
+				"foo": cty.StringVal("bar"),
+			})}),
+			"list(\n    object({\n        foo: string,\n    }),\n)",
+		},
+		// Unknowns and Nulls
+		{
+			cty.UnknownVal(cty.String),
+			"string",
+		},
+		{
+			cty.NullVal(cty.Object(map[string]cty.Type{
+				"foo": cty.String,
+			})),
+			"object({\n    foo: string,\n})",
+		},
+		{ // irrelevant marks do nothing
+			cty.ListVal([]cty.Value{cty.ObjectVal(map[string]cty.Value{
+				"foo": cty.StringVal("bar").Mark("ignore me"),
+			})}),
+			"list(\n    object({\n        foo: string,\n    }),\n)",
+		},
+	}
+	for _, test := range tests {
+		got, err := Type([]cty.Value{test.Input})
+		if err != nil {
+			t.Fatalf("unexpected error: %s", err)
+		}
+		// The value is marked to help with formatting
+		got, _ = got.Unmark()
+
+		if got.AsString() != test.Want {
+			t.Errorf("wrong result:\n%s", cmp.Diff(got.AsString(), test.Want))
+		}
+	}
+}

lang/functions.go

@@ -152,6 +152,11 @@ func (s *Scope) Functions() map[string]function.Function {
 			return s.funcs
 		})
 
+		if s.ConsoleMode {
+			// The type function is only available in terraform console.
+			s.funcs["type"] = funcs.TypeFunc
+		}
+
 		if s.PureOnly {
 			// Force our few impure functions to return unknown so that we
 			// can defer evaluating them until a later pass.

lang/scope.go

@@ -37,6 +37,10 @@ type Scope struct {
 	// considered as active in the module that this scope will be used for.
 	// Callers can populate it by calling the SetActiveExperiments method.
 	activeExperiments experiments.Set
+
+	// ConsoleMode can be set to true to request any console-only functions are
+	// included in this scope.
+	ConsoleMode bool
 }
 
 // SetActiveExperiments allows a caller to declare that a set of experiments

repl/format.go

@@ -16,7 +16,11 @@ func FormatValue(v cty.Value, indent int) string {
 	if !v.IsKnown() {
 		return "(known after apply)"
 	}
-	if v.IsMarked() {
+	if v.Type().Equals(cty.String) && v.HasMark("raw") {
+		raw, _ := v.Unmark()
+		return raw.AsString()
+	}
+	if v.HasMark("sensitive") {
 		return "(sensitive)"
 	}
 	if v.IsNull() {

website/docs/configuration/functions/type.html.md

@@ -0,0 +1,82 @@
+---
+layout: "language"
+page_title: "type - Functions - Configuration Language"
+sidebar_current: "docs-funcs-conversion-type"
+description: |-
+  The type function returns the type of a given value. 
+---
+
+# `type` Function
+
+-> **Note:** This function is available only in Terraform 1.0 and later.
+
+`type` retuns the type of a given value.
+
+Sometimes a Terraform configuration can result in confusing errors regarding
+inconsistent types. This function displays terraform's evaluation of a given
+value's type, which is useful in understanding this error message.
+
+This is a special function which is only available in the `terraform console` command.
+
+## Examples
+
+Here we have a conditional `output` which prints either the value of `var.list` or a local named `default_list`: 
+
+```hcl
+variable "list" {
+  default = []
+}
+
+locals {
+  default_list = [
+    {
+      foo = "bar"
+      map = { bleep = "bloop" }
+    },
+    {
+      beep = "boop"
+    },
+  ]
+}
+
+output "list" {
+  value = var.list != [] ? var.list : local.default_list
+}
+```
+
+Applying this configuration results in the following error:
+
+```
+Error: Inconsistent conditional result types
+
+  on main.tf line 18, in output "list":
+  18:   value = var.list != [] ? var.list : local.default_list
+    |----------------
+    | local.default_list is tuple with 2 elements
+    | var.list is empty tuple
+
+The true and false result expressions must have consistent types. The given
+expressions are tuple and tuple, respectively.
+```
+
+While this error message does include some type information, it can be helpful
+to inspect the exact type that Terraform has determined for each given input.
+Examining both `var.list` and `local.default_list` using the `type` function
+provides more context for the error message:
+
+```
+> type(var.list)
+tuple
+> type(local.default_list)
+tuple([
+    object({
+        foo: string,
+        map: object({
+            bleep: string,
+        }),
+    }),
+    object({
+        beep: string,
+    }),
+])
+```