lang: Print a clear message on module import containing unused stmt

If you run an import, you only include everything that's part of a
scope. This includes, variables, classes, and functions. Anything else
should cause a compile error. This cleans up the error by adding a
String() method to each Stmt in our AST.

lang/interfaces/ast.go

@@ -40,6 +40,7 @@ type Node interface {
 // expression.)
 type Stmt interface {
 	Node
+	fmt.Stringer                 // String() string
 	Init(*Data) error            // initialize the populated node and validate
 	Interpolate() (Stmt, error)  // return expanded form of AST as a new AST
 	SetScope(*Scope) error       // set the scope here and propagate it downwards
@@ -54,6 +55,7 @@ type Stmt interface {
 // these can be stored as pointers in our graph data structure.
 type Expr interface {
 	Node
+	//fmt.Stringer // already provided by pgraph.Vertex
 	pgraph.Vertex               // must implement this since we store these in our graphs
 	Init(*Data) error           // initialize the populated node and validate
 	Interpolate() (Expr, error) // return expanded form of AST as a new AST

lang/interpret_test/TestAstFunc1/unused1.graph

@@ -0,0 +1 @@
+# err: import scope `something.mcl` failed: local import of `something.mcl` failed: module contains unused statements: found stmt: res(print)

lang/interpret_test/TestAstFunc1/unused1/main.mcl

@@ -0,0 +1,7 @@
+import "fmt"
+import "something.mcl"
+
+include something.someclass
+print "p1" {
+	msg => fmt.printf("someint: %d", $something.someint),
+}

lang/interpret_test/TestAstFunc1/unused1/something.mcl

@@ -0,0 +1,11 @@
+$someint = 42
+class someclass {
+	print "p2" {
+		msg => "i'm inside of someclass",
+	}
+}
+
+# this should generate a compile error
+print "unused" {
+	msg => "i'm unused because i'm inside an imported module",
+}

lang/structs.go

@@ -90,6 +90,11 @@ func (obj *StmtBind) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtBind) String() string {
+	return fmt.Sprintf("bind(%s)", obj.Ident)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtBind) Init(data *interfaces.Data) error {
@@ -181,6 +186,11 @@ func (obj *StmtRes) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtRes) String() string {
+	return fmt.Sprintf("res(%s)", obj.Kind)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtRes) Init(data *interfaces.Data) error {
@@ -1406,6 +1416,11 @@ func (obj *StmtEdge) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtEdge) String() string {
+	return "edge" // TODO: improve this
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtEdge) Init(data *interfaces.Data) error {
@@ -1731,6 +1746,11 @@ func (obj *StmtIf) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtIf) String() string {
+	return "if" // TODO: improve this
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtIf) Init(data *interfaces.Data) error {
@@ -1948,6 +1968,11 @@ func (obj *StmtProg) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtProg) String() string {
+	return "prog" // TODO: improve this
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtProg) Init(data *interfaces.Data) error {
@@ -2678,8 +2703,8 @@ func (obj *StmtProg) IsModuleUnsafe() error { // TODO: rename this function?
 		case *StmtComment: // possibly not even parsed
 			// all of these are safe
 		default:
-			// something else unsafe
-			return fmt.Errorf("found unsafe stmt: %v", x)
+			// something else unsafe (unused)
+			return fmt.Errorf("found stmt: %s", x.String())
 		}
 	}
 	return nil
@@ -2706,6 +2731,11 @@ func (obj *StmtFunc) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtFunc) String() string {
+	return fmt.Sprintf("func(%s)", obj.Name)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtFunc) Init(data *interfaces.Data) error {
@@ -2787,6 +2817,11 @@ func (obj *StmtClass) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtClass) String() string {
+	return fmt.Sprintf("class(%s)", obj.Name)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtClass) Init(data *interfaces.Data) error {
@@ -2879,6 +2914,11 @@ func (obj *StmtInclude) Apply(fn func(interfaces.Node) error) error {
 	return fn(obj)
 }
 
+// String returns a short representation of this statement.
+func (obj *StmtInclude) String() string {
+	return fmt.Sprintf("include(%s)", obj.Name)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtInclude) Init(data *interfaces.Data) error {
@@ -3089,6 +3129,11 @@ type StmtImport struct {
 // a select number of node types, since they won't need extra noop iterators...
 func (obj *StmtImport) Apply(fn func(interfaces.Node) error) error { return fn(obj) }
 
+// String returns a short representation of this statement.
+func (obj *StmtImport) String() string {
+	return fmt.Sprintf("import(%s)", obj.Name)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtImport) Init(*interfaces.Data) error { return nil }
@@ -3155,6 +3200,11 @@ type StmtComment struct {
 // a select number of node types, since they won't need extra noop iterators...
 func (obj *StmtComment) Apply(fn func(interfaces.Node) error) error { return fn(obj) }
 
+// String returns a short representation of this statement.
+func (obj *StmtComment) String() string {
+	return fmt.Sprintf("comment(%s)", obj.Value)
+}
+
 // Init initializes this branch of the AST, and returns an error if it fails to
 // validate.
 func (obj *StmtComment) Init(*interfaces.Data) error {