Consider typed, value-less variables to have null value

A variable with a type but no default value or override resulted in an
empty string.  This matches the legacy behavior of untyped variables,
but does not make sense when using types (an empty string is itself a
type violation for everything except `string`).  All variables defined
with a type but with no value are now a typed `null`.

A variable explicitly typed `any` was previously treated as if the
typing was omitted; with no defined value or override, that resulted in
an empty string.  The `any` type is now distinguished from an omitted
type; these variables, with no default or override, are also `null`.

In other respects, the behavior of `any` is unchanged and largely
behaves as if the type was omitted.  It's not clear whether it should be
 supported, let alone how it should behave, so these tests were removed.
It's being treated as undefined behavior.

Signed-off-by: Roberto Villarreal <rrjjvv@yahoo.com>

bake/hcl_test.go

@@ -423,6 +423,63 @@ func TestHCLNullVariables(t *testing.T) {
 	require.Equal(t, ptrstr("bar"), c.Targets[0].Args["foo"])
 }
 
+func TestHCLTypedNullVariables(t *testing.T) {
+	types := []string{
+		"any",
+		"string", "number", "bool",
+		"list(string)", "set(string)", "map(string)",
+		"tuple([string])", "object({val: string})",
+	}
+	for _, varType := range types {
+		tName := fmt.Sprintf("variable typed %q with null default remains null", varType)
+		t.Run(tName, func(t *testing.T) {
+			dt := fmt.Sprintf(`
+	            variable "FOO" {
+	                type = %s
+	                default = null
+	            }
+	
+	            target "default" {
+	                args = {
+	                    foo = equal(FOO, null)
+	                }
+	            }`, varType)
+			c, err := ParseFile([]byte(dt), "docker-bake.hcl")
+			require.NoError(t, err)
+			require.Equal(t, 1, len(c.Targets))
+			require.Equal(t, "true", *c.Targets[0].Args["foo"])
+		})
+	}
+}
+
+func TestHCLTypedValuelessVariables(t *testing.T) {
+	types := []string{
+		"any",
+		"string", "number", "bool",
+		"list(string)", "set(string)", "map(string)",
+		"tuple([string])", "object({val: string})",
+	}
+	for _, varType := range types {
+		tName := fmt.Sprintf("variable typed %q with no default is null", varType)
+		t.Run(tName, func(t *testing.T) {
+			dt := fmt.Sprintf(`
+                variable "FOO" {
+                    type = %s
+                }
+
+                target "default" {
+                    args = {
+                        foo = equal(FOO, null)
+                    }
+                }`, varType)
+			c, err := ParseFile([]byte(dt), "docker-bake.hcl")
+			require.NoError(t, err)
+			require.Equal(t, 1, len(c.Targets))
+			require.Equal(t, "true", *c.Targets[0].Args["foo"])
+		})
+	}
+}
+
 func TestJSONNullVariables(t *testing.T) {
 	dt := []byte(`{
 		"variable": {
@@ -1877,19 +1934,6 @@ func TestTypedVarOverrides(t *testing.T) {
 			override:  `"hello"`,
 			wantValue: `"hello"`,
 		},
-		{
-			name:      "any",
-			varType:   "any",
-			override:  "[1,2]",
-			wantValue: "[1,2]",
-		},
-		{
-			name:         "any never convert to complex types",
-			varType:      "any",
-			override:     "[1,2]",
-			argValue:     "length(FOO)",
-			wantErrorMsg: "collection must be a list",
-		},
 		{
 			name:      "proper CSV list of strings",
 			varType:   "list(string)",
@@ -2090,19 +2134,6 @@ func TestTypedVarOverrides_JSON(t *testing.T) {
 			override:  `"hello"`,
 			wantValue: "hello",
 		},
-		{
-			name:      "any",
-			varType:   "any",
-			override:  "[1,2]",
-			wantValue: "[1,2]",
-		},
-		{
-			name:         "any never convert to complex types",
-			varType:      "any",
-			override:     "[1,2]",
-			argValue:     "length(FOO)",
-			wantErrorMsg: "collection must be a list",
-		},
 		{
 			name:      "list of strings",
 			varType:   "list(string)",
@@ -2313,6 +2344,7 @@ func TestJSONOverridePriority(t *testing.T) {
 		dt := []byte(`
             variable "foo" {
                 type = number
+                default = 101
             }
             
             target "default" {
@@ -2325,8 +2357,7 @@ func TestJSONOverridePriority(t *testing.T) {
 		c, err := ParseFile(dt, "docker-bake.hcl")
 		require.NoError(t, err)
 		require.Equal(t, 1, len(c.Targets))
-		// a variable with no value has always resulted in an empty string
-		require.Equal(t, "", *c.Targets[0].Args["bar"])
+		require.Equal(t, "101", *c.Targets[0].Args["bar"])
 
 		t.Setenv("foo_JSON", "42")
 		c, err = ParseFile(dt, "docker-bake.hcl")

bake/hclparser/hclparser.go

@@ -282,7 +282,7 @@ func (p *parser) resolveValue(ectx *hcl.EvalContext, name string) (err error) {
 	}
 
 	var diags hcl.Diagnostics
-	varType := cty.DynamicPseudoType
+	varType, typeSpecified := cty.DynamicPseudoType, false
 	def, ok := p.attrs[name]
 	if !ok {
 		vr, ok := p.vars[name]
@@ -295,12 +295,13 @@ func (p *parser) resolveValue(ectx *hcl.EvalContext, name string) (err error) {
 		if diags.HasErrors() {
 			return diags
 		}
+		typeSpecified = !varType.Equals(cty.DynamicPseudoType) || hcl.ExprAsKeyword(vr.Type) == "any"
 	}
 
 	if def == nil {
-		// lack of specified value is considered to have an empty string value,
-		// but any overrides get type checked
-		if _, ok, _ := p.valueHasOverride(name, false); !ok {
+		// Lack of specified value, when untyped is considered to have an empty string value.
+		// A typed variable with no value will result in (typed) nil.
+		if _, ok, _ := p.valueHasOverride(name, false); !ok && !typeSpecified {
 			vv := cty.StringVal("")
 			v = &vv
 			return
@@ -322,9 +323,6 @@ func (p *parser) resolveValue(ectx *hcl.EvalContext, name string) (err error) {
 		}
 	}
 
-	// Not entirely true... this doesn't differentiate between a user that specified 'any'
-	// and a user that specified nothing.  But the result is the same; both are treated as strings.
-	typeSpecified := !varType.Equals(cty.DynamicPseudoType)
 	envv, hasEnv, jsonEnv := p.valueHasOverride(name, typeSpecified)
 	_, isVar := p.vars[name]