feat: add extVarWithDefault as builtin to support extVar with a default value

core/desugarer.cpp

@@ -36,7 +36,7 @@ struct BuiltinDecl {
     std::vector<UString> params;
 };
 
-static unsigned long max_builtin = 40;
+static unsigned long max_builtin = 41;
 BuiltinDecl jsonnet_builtin_decl(unsigned long builtin)
 {
     switch (builtin) {
@@ -81,6 +81,7 @@ BuiltinDecl jsonnet_builtin_decl(unsigned long builtin)
         case 38: return {U"decodeUTF8", {U"arr"}};
         case 39: return {U"atan2", {U"y", U"x"}};
         case 40: return {U"hypot", {U"a", U"b"}};
+        case 41: return {U"extVarWithDefault", {U"x", U"default"}};
         default:
             std::cerr << "INTERNAL ERROR: Unrecognized builtin function: " << builtin << std::endl;
             std::abort();

core/vm.cpp

@@ -973,6 +973,7 @@ class Interpreter {
         builtins["decodeUTF8"] = &Interpreter::builtinDecodeUTF8;
         builtins["atan2"] = &Interpreter::builtinAtan2;
         builtins["hypot"] = &Interpreter::builtinHypot;
+        builtins["extVarWithDefault"] = &Interpreter::builtinExtVarWithDefault;
 
         DesugaredObject *stdlib = makeStdlibAST(alloc, "__internal__");
         jsonnet_static_analysis(stdlib);
@@ -1343,15 +1344,11 @@ class Interpreter {
         return nullptr;
     }
 
-    const AST *builtinExtVar(const LocationRange &loc, const std::vector<Value> &args)
+    const AST *getExtVarOrValue(const std::string &var8, Value *outValue = nullptr)
     {
-        validateBuiltinArgs(loc, "extVar", args, {Value::STRING});
-        const UString &var = static_cast<HeapString *>(args[0].v.h)->value;
-        std::string var8 = encode_utf8(var);
         auto it = externalVars.find(var8);
         if (it == externalVars.end()) {
-            std::string msg = "undefined external variable: " + var8;
-            throw makeError(loc, msg);
+            return nullptr;
         }
         const VmExt &ext = it->second;
         if (ext.isCode) {
@@ -1363,9 +1360,58 @@ class Interpreter {
             stack.pop();
             return expr;
         } else {
-            scratch = makeString(decode_utf8(ext.data));
+            if (outValue) *outValue = makeString(decode_utf8(ext.data));
+            return nullptr;
+        }
+    }
+
+    const AST *builtinExtVar(const LocationRange &loc, const std::vector<Value> &args)
+    {
+        validateBuiltinArgs(loc, "extVar", args, {Value::STRING});
+        const UString &var = static_cast<HeapString *>(args[0].v.h)->value;
+        std::string var8 = encode_utf8(var);
+        Value result;
+        const AST *expr = getExtVarOrValue(var8, &result);
+        if (expr) {
+            return expr;
+        } else if (result.t == Value::STRING) {
+            scratch = result;
+            return nullptr;
+        } else {
+            std::string msg = "undefined external variable: " + var8;
+            throw makeError(loc, msg);
+        }
+    }
+
+    const AST *builtinExtVarWithDefault(const LocationRange &loc, const std::vector<Value> &args)
+    {
+        if (args.size() != 2) {
+            std::stringstream ss;
+            ss << "extVarWithDefault expects 2 arguments, got " << args.size();
+            throw makeError(loc, ss.str());
+        }
+        for (int i = 0; i < 2; ++i) {
+            Value::Type t = args[i].t;
+            if (t != Value::STRING && t != Value::NUMBER && t != Value::BOOLEAN &&
+                t != Value::NULL_TYPE && t != Value::OBJECT) {
+                std::stringstream ss;
+                ss << "extVarWithDefault argument " << (i + 1)
+                   << " must be string, number, boolean, null, or object, got " << type_str(args[i]);
+                throw makeError(loc, ss.str());
+            }
+        }
+        const UString &var = static_cast<HeapString *>(args[0].v.h)->value;
+        std::string var8 = encode_utf8(var);
+        Value result;
+        const AST *expr = getExtVarOrValue(var8, &result);
+        if (expr) {
+            return expr;
+        } else if (result.t == Value::STRING) {
+            scratch = result;
             return nullptr;
         }
+        scratch = args[1];
+        return nullptr;
     }
 
     const AST *builtinPrimitiveEquals(const LocationRange &loc, const std::vector<Value> &args)

test_cmd/extWithDefault1.golden.stdout

@@ -0,0 +1 @@
+"1"

test_cmd/extWithDefault2.golden.stdout

@@ -0,0 +1 @@
+"1"

test_cmd/extWithDefault3.golden.stdout

@@ -0,0 +1 @@
+"default"

test_cmd/extWithDefault4.golden.stdout

@@ -0,0 +1 @@
+2

test_cmd/extWithDefault5.golden.stdout

@@ -0,0 +1 @@
+"hi\n"

test_cmd/extWithDefault6.golden.stdout

@@ -0,0 +1,5 @@
+{
+   "a": 1,
+   "b": 2,
+   "c": 3
+}

test_cmd/extWithDefault7.golden.stdout

@@ -0,0 +1 @@
+"lib3_test.jsonnet"

test_cmd/run_cmd_tests.sh

@@ -69,6 +69,27 @@ do_test "ext4" 0 --ext-code x=1+1 -e 'std.extVar("x")'
 do_test "ext5" 0 --ext-str-file "x=test.txt" -e 'std.extVar("x")'
 do_test "ext6" 0 --ext-code-file "x=test.jsonnet" -e 'std.extVar("x")'
 do_test "ext7" 0 --ext-code-file "x=lib1/lib3_test.jsonnet" -e 'std.extVar("x")'
+if do_test "extWithDefault1" 0 --ext-str x=1 -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault1" "out/extWithDefault1/stdout" "extWithDefault1.golden.stdout"
+fi
+if do_test "extWithDefault2" 0 -V x=1 -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault2" "out/extWithDefault2/stdout" "extWithDefault2.golden.stdout"
+fi
+if do_test "extWithDefault3" 0 -V y=1 -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault3" "out/extWithDefault3/stdout" "extWithDefault3.golden.stdout"
+fi
+if do_test "extWithDefault4" 0 --ext-code x=1+1 -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault4" "out/extWithDefault4/stdout" "extWithDefault4.golden.stdout"
+fi
+if do_test "extWithDefault5" 0 --ext-str-file "x=test.txt" -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault5" "out/extWithDefault5/stdout" "extWithDefault5.golden.stdout"
+fi
+if do_test "extWithDefault6" 0 --ext-code-file "x=test.jsonnet" -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault6" "out/extWithDefault6/stdout" "extWithDefault6.golden.stdout"
+fi
+if do_test "extWithDefault7" 0 --ext-code-file "x=lib1/lib3_test.jsonnet" -e 'std.extVarWithDefault("x", "default")'; then
+    check_file "extWithDefault7" "out/extWithDefault7/stdout" "extWithDefault7.golden.stdout"
+fi
 do_test "tla1" 0 --tla-str x=1 -e 'function(x) x'
 do_test "tla2" 0 -A x=1 -e 'function(x) x'
 do_test "tla3" 1 -A y=1 -e 'function(x) x'

test_suite/stdlib.jsonnet

@@ -516,6 +516,11 @@ std.assertEqual(std.toString(std.extVar('var2')), '{"x": 1, "y": 2}') &&
 std.assertEqual(std.extVar('var2'), { x: 1, y: 2 }) &&
 std.assertEqual(std.extVar('var2') { x+: 2 }.x, 3) &&
 
+std.assertEqual(std.extVarWithDefault('var1', 'default'), 'test') &&
+std.assertEqual(std.extVarWithDefault('missing', 'default'), 'default') &&
+std.assertEqual(std.extVarWithDefault('var2', { x: 0, y: 0 }), { x: 1, y: 2 }) &&
+std.assertEqual(std.extVarWithDefault('missingObj', { x: 0, y: 0 }), { x: 0, y: 0 }) &&
+
 std.assertEqual(std.split('foo/bar', '/'), ['foo', 'bar']) &&
 std.assertEqual(std.split('/foo/', '/'), ['', 'foo', '']) &&
 std.assertEqual(std.split('foo/_bar', '/_'), ['foo', 'bar']) &&