Implement std.isEmpty for string (google#678)

* Implement std.isEmpty for string

Author: Tejesh-Raut

builtins.go

@@ -1279,6 +1279,15 @@ func builtinStrReplace(i *interpreter, strv, fromv, tov value) (value, error) {
 	return makeValueString(strings.Replace(sStr, sFrom, sTo, -1)), nil
 }
 
+func builtinIsEmpty(i *interpreter, strv value) (value, error) {
+	str, err := i.getString(strv)
+	if err != nil {
+		return nil, err
+	}
+	sStr := str.getGoString()
+	return makeValueBoolean(len(sStr) == 0), nil
+}
+
 func base64DecodeGoBytes(i *interpreter, str string) ([]byte, error) {
 	strLen := len(str)
 	if strLen%4 != 0 {
@@ -1495,7 +1504,7 @@ func tomlEncodeString(s string) string {
 }
 
 // tomlEncodeKey encodes a key - returning same string if it does not need quoting,
-// otherwise return it quoted; returns empty key as ''
+// otherwise return it quoted; returns empty key as ”
 func tomlEncodeKey(s string) string {
 	bareAllowed := true
 
@@ -2218,6 +2227,7 @@ var funcBuiltins = buildBuiltinMap([]builtin{
 	&ternaryBuiltin{name: "substr", function: builtinSubstr, params: ast.Identifiers{"str", "from", "len"}},
 	&ternaryBuiltin{name: "splitLimit", function: builtinSplitLimit, params: ast.Identifiers{"str", "c", "maxsplits"}},
 	&ternaryBuiltin{name: "strReplace", function: builtinStrReplace, params: ast.Identifiers{"str", "from", "to"}},
+	&unaryBuiltin{name: "isEmpty", function: builtinIsEmpty, params: ast.Identifiers{"str"}},
 	&unaryBuiltin{name: "base64Decode", function: builtinBase64Decode, params: ast.Identifiers{"str"}},
 	&unaryBuiltin{name: "base64DecodeBytes", function: builtinBase64DecodeBytes, params: ast.Identifiers{"str"}},
 	&unaryBuiltin{name: "parseInt", function: builtinParseInt, params: ast.Identifiers{"str"}},

linter/internal/types/stdlib.go

@@ -88,6 +88,7 @@ func prepareStdlib(g *typeGraph) {
 		"asciiLower":  g.newSimpleFuncType(stringType, "str"),
 		"stringChars": g.newSimpleFuncType(stringType, "str"),
 		"format":      g.newSimpleFuncType(stringType, "str", "vals"),
+		"isEmpty":     g.newSimpleFuncType(boolType, "str"),
 		// TODO(sbarzowski) Fix when they match the documentation
 		"escapeStringBash":    g.newSimpleFuncType(stringType, "str_"),
 		"escapeStringDollars": g.newSimpleFuncType(stringType, "str_"),

testdata/builtinIsEmpty.golden

@@ -0,0 +1 @@
+true

testdata/builtinIsEmpty.jsonnet

@@ -0,0 +1 @@
+std.isEmpty("")

testdata/builtinIsEmpty.linter.golden

@@ -0,0 +1 @@
+false

testdata/builtinIsEmpty1.golden

@@ -0,0 +1 @@
+std.isEmpty("non-empty string")

testdata/builtinIsEmpty1.jsonnet

@@ -0,0 +1,9 @@
+RUNTIME ERROR: Unexpected type number, expected string
+-------------------------------------------------
+	testdata/builtinIsEmpty2:1:1-16	$
+
+std.isEmpty(10)
+
+-------------------------------------------------
+	During evaluation
+

testdata/builtinIsEmpty1.linter.golden

@@ -0,0 +1 @@
+std.isEmpty(10)