lang: Fix non-string key panics in map function

The map function assumed that the key arguments were strings, and would
panic if they were not.

After this commit, calling `map(1, 2)` will result in a map `{"1" = 1}`,
and calling `map(null, 1)` will result in a syntax error.

Fixes #23346, fixes #23043

lang/funcs/collection.go

@@ -346,12 +346,14 @@ var MapFunc = function.New(&function.Spec{
 
 		for i := 0; i < len(args); i += 2 {
 
-			key := args[i].AsString()
+			keyVal, err := convert.Convert(args[i], cty.String)
-
-			err := gocty.FromCtyValue(args[i], &key)
 			if err != nil {
 				return cty.NilVal, err
 			}
+			if keyVal.IsNull() {
+				return cty.NilVal, fmt.Errorf("argument %d is a null key", i+1)
+			}
+			key := keyVal.AsString()
 
 			val := args[i+1]
 

lang/funcs/collection_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/function"
 )
 
 func TestLength(t *testing.T) {
@@ -730,6 +731,19 @@ func TestMap(t *testing.T) {
 			}),
 			false,
 		},
+		{ // convert number keys to strings
+			[]cty.Value{
+				cty.NumberIntVal(1),
+				cty.StringVal("hello"),
+				cty.NumberIntVal(2),
+				cty.StringVal("goodbye"),
+			},
+			cty.MapVal(map[string]cty.Value{
+				"1": cty.StringVal("hello"),
+				"2": cty.StringVal("goodbye"),
+			}),
+			false,
+		},
 		{ // map of lists is okay
 			[]cty.Value{
 				cty.StringVal("hello"),
@@ -785,6 +799,14 @@ func TestMap(t *testing.T) {
 			cty.NilVal,
 			true,
 		},
+		{ // null key returns an error
+			[]cty.Value{
+				cty.NullVal(cty.DynamicPseudoType),
+				cty.NumberIntVal(5),
+			},
+			cty.NilVal,
+			true,
+		},
 	}
 
 	for _, test := range tests {
@@ -794,6 +816,9 @@ func TestMap(t *testing.T) {
 				if err == nil {
 					t.Fatal("succeeded; want error")
 				}
+				if _, ok := err.(function.PanicError); ok {
+					t.Fatalf("unexpected panic: %s", err)
+				}
 				return
 			} else if err != nil {
 				t.Fatalf("unexpected error: %s", err)