internal/core/compile: add version check for builtins

Right now we only do this for predeclared
identifiers. Note, however, that by
taking the Runtime, instead of an
Indexer, we can lookup stdlib packages
and implement the same for stdlib calls.

Issue #291
Issue #943

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I667b713fbb0808ced0cbc76445083b097edfa6da
Dispatch-Trailer: {"type":"trybot","CL":1217324,"patchset":2,"ref":"refs/changes/24/1217324/2","targetBranch":"master"}

Author: mpvl

cue/testdata/builtins/error.txtar

@@ -1,3 +1,6 @@
+-- cue.mod/module.cue --
+module: "cuelang.org/error"
+language: version: "v0.14.0"
 -- in.cue --
 selection: {
 	dropError: 1 | error("drop me")

cue/testdata/builtins/versionchk.txtar

@@ -0,0 +1,16 @@
+-- cue.mod/module.cue --
+module: "cuelang.org/go/internal/core/adt/eval_test"
+language: version: "v0.8.0"
+-- in.cue --
+// error is not yet available in v0.8.0.
+a: error("msg")
+-- out/eval --
+a: builtin "error" is not available in version v0.8.0; it was added in version "v0.14.0":
+    ./in.cue:2:4
+-- out/compile --
+a: builtin "error" is not available in version v0.8.0; it was added in version "v0.14.0":
+    ./in.cue:2:4
+--- in.cue
+{
+  a: _|_(builtin "error" is not available in version v0.8.0; it was added in version "v0.14.0")("msg")
+}

internal/core/adt/expr.go

@@ -1669,6 +1669,9 @@ type Builtin struct {
 	// TODO: consider merging Func and RawFunc into a single field again.
 	RawFunc func(call *CallContext) Value
 
+	// Added indicates as of which language version this builtin can be used.
+	Added string
+
 	Package Feature
 	Name    string
 }

internal/core/compile/builtin.go

@@ -38,7 +38,9 @@ var (
 // message. If the argument is an interpolation, it will be evaluated and if it
 // results in an error, the argument will be inserted as an expression.
 var errorBuiltin = &adt.Builtin{
-	Name:   "error",
+	Name:  "error",
+	Added: "v0.14.0",
+
 	Params: []adt.Param{stringParam},
 	Result: adt.BottomKind,
 	RawFunc: func(call *adt.CallContext) adt.Value {

internal/core/compile/compile.go

@@ -25,6 +25,7 @@ import (
 	"cuelang.org/go/internal/astinternal"
 	"cuelang.org/go/internal/core/adt"
 	"cuelang.org/go/internal/cueexperiment"
+	"cuelang.org/go/internal/mod/semver"
 )
 
 // A Scope represents a nested scope of Vertices.
@@ -333,6 +334,34 @@ func (c *compiler) compileExpr(x ast.Expr) adt.Conjunct {
 	return adt.MakeRootConjunct(env, expr)
 }
 
+// verifyVersion checks whether n is a Builtin and then checks whether the
+// Added version is compatible with the file version registered in c.
+func (c *compiler) verifyVersion(src ast.Node, n adt.Expr) adt.Expr {
+	b, ok := n.(*adt.Builtin)
+	if !ok {
+		return n
+	}
+	if b.Added == "" {
+		// No version check needed.
+		return n
+	}
+	v := c.experiments.LanguageVersion()
+	if v == "" {
+		// We assume "latest" if the file is not associated with a version.
+		return n
+	}
+
+	if semver.Compare(b.Added, v) <= 0 {
+		// The feature is available in the file version.
+		return n
+	}
+
+	// The feature is not available in the file version.
+	// NonConcrete builtins are not allowed in older versions.
+	return c.errf(src, "builtin %q is not available in version %v; "+
+		"it was added in version %q", b.Name, v, b.Added)
+}
+
 // resolve assumes that all existing resolutions are legal. Validation should
 // be done in a separate step if required.
 //
@@ -396,7 +425,7 @@ func (c *compiler) resolve(n *ast.Ident) adt.Expr {
 		}
 
 		if p := predeclared(n); p != nil {
-			return p
+			return c.verifyVersion(n, p)
 		}
 
 		return c.errf(n, "reference %q not found", n.Name)
@@ -902,9 +931,14 @@ func (c *compiler) expr(expr ast.Expr) adt.Expr {
 
 	case *ast.SelectorExpr:
 		c.inSelector++
+		x := c.expr(n.X)
+		// TODO: check if x is an ImportReference, and if so, check if it a
+		// standard library, look up the builtin, and check its version. The
+		// index of standard libraries is available in c.index, which is really
+		// an adt.Runtime under the hood.
 		ret := &adt.SelectorExpr{
 			Src: n,
-			X:   c.expr(n.X),
+			X:   x,
 			Sel: c.label(n.Sel)}
 		c.inSelector--
 		return ret

internal/cueexperiment/file.go

@@ -53,6 +53,12 @@ type File struct {
 	StructCmp bool `experiment:"since:v0.14.0"`
 }
 
+// LanguageVersion returns the language version of the file or "" if no language
+// version is associated with it.
+func (f *File) LanguageVersion() string {
+	return f.version
+}
+
 // NewFile parses the given comma-separated list of experiments for
 // the given version and returns a PerFile struct with the experiments enabled.
 // A empty version indicates the default version.