Avoid depending on stdlib variable for desugaring.

The fix is easy – we just use "$std" which the user cannot access,
because it's not a valid identifier.

internal/program/desugarer.go

@@ -251,7 +251,7 @@ func buildSimpleIndex(obj ast.Node, member ast.Identifier) ast.Node {
 }
 
 func buildStdCall(builtinName ast.Identifier, loc ast.LocationRange, args ...ast.Node) ast.Node {
-	std := &ast.Var{Id: "std"}
+	std := &ast.Var{Id: "$std"}
 	builtin := buildSimpleIndex(std, builtinName)
 	positional := make([]ast.CommaSeparatedExpr, len(args))
 	for i := range args {

internal/program/static_analyzer.go

@@ -164,5 +164,5 @@ func analyzeVisit(a ast.Node, inObject bool, vars ast.IdentifierSet) error {
 // It enriches the AST with additional information about free variables in every node,
 // so it is necessary to always run it before executing the AST.
 func analyze(node ast.Node) error {
-	return analyzeVisit(node, false, ast.NewIdentifierSet("std"))
+	return analyzeVisit(node, false, ast.NewIdentifierSet("std", "$std"))
 }

interpreter.go

@@ -1183,8 +1183,16 @@ func buildStdObject(i *interpreter) (*valueObject, error) {
 }
 
 func evaluateStd(i *interpreter) (value, error) {
+	// We are bootstrapping std before it is properly available.
+	// We need "$std" for desugaring.
+	// So, we're creating an empty thunk (evaluating will panic).
+	// We will fill it manually before it's evaluated, though.
+	// This "std" does not have std.thisFile.
+	stdThunk := &cachedThunk{}
 	beforeStdEnv := makeEnvironment(
-		bindingFrame{},
+		bindingFrame{
+			"$std": stdThunk,
+		},
 		makeUnboundSelfBinding(),
 	)
 	evalLoc := ast.MakeLocationRangeMessage("During evaluation of std")
@@ -1192,7 +1200,12 @@ func evaluateStd(i *interpreter) (value, error) {
 	node := astgen.StdAst
 	i.stack.setCurrentTrace(evalTrace)
 	defer i.stack.clearCurrentTrace()
-	return i.EvalInCleanEnv(&beforeStdEnv, node, false)
+	content, err := i.EvalInCleanEnv(&beforeStdEnv, node, false)
+	if err != nil {
+		return nil, err
+	}
+	stdThunk.content = content
+	return content, nil
 }
 
 func prepareExtVars(i *interpreter, ext vmExtMap, kind string) map[string]*cachedThunk {
@@ -1243,9 +1256,13 @@ func makeInitialEnv(filename string, baseStd *valueObject) environment {
 	fileSpecific := buildObject(ast.ObjectFieldHidden, map[string]value{
 		"thisFile": makeValueString(filename),
 	})
+
+	stdThunk := readyThunk(makeValueExtendedObject(baseStd, fileSpecific))
+
 	return makeEnvironment(
 		bindingFrame{
-			"std": readyThunk(makeValueExtendedObject(baseStd, fileSpecific)),
+			"std":  stdThunk,
+			"$std": stdThunk, // Unavailable to the user. To be used with desugaring.
 		},
 		makeUnboundSelfBinding(),
 	)

linter/linter.go

@@ -62,7 +62,7 @@ func lint(vm *jsonnet.VM, nodes []nodeWithLocation, errWriter *ErrorWriter) {
 	}
 
 	findVariables := func(node nodeWithLocation) *common.VariableInfo {
-		return variables.FindVariables(node.node, variables.Environment{"std": &std})
+		return variables.FindVariables(node.node, variables.Environment{"std": &std, "$std": &std})
 	}
 
 	for importedPath, rootNode := range roots {

testdata/overriding_stdlib_desugared.golden

@@ -0,0 +1,6 @@
+[
+   { },
+   [ ],
+   42,
+   false
+]

testdata/overriding_stdlib_desugared.jsonnet

@@ -0,0 +1,8 @@
+// Make sure shadowing std does not cause problems for desugaring.
+local std = {};
+[
+    { [x]: 17 for x in [] },
+    [ x for x in [] ],
+    42 % 2137,
+    "foo" in {},
+]

testdata/overriding_stdlib_desugared.linter.golden

@@ -0,0 +1,5 @@
+../testdata/overriding_stdlib_desugared:2:7-15 Unused variable: std
+
+local std = {};
+
+