lang: ast: Ensure a list doesn't sneak through type interpolation

If we had a single list wrapped in an interpolated string, it could
sneak through type unification, which is not correct. Wrapping a
variable by interpolation in a string, must force it to be a string.

lang/ast/structs.go

@@ -5408,6 +5408,10 @@ func (obj *ExprStr) Interpolate() (interfaces.Expr, error) {
 		}, nil
 	}
 	// we got something, overwrite the existing static str
+	// ensure str, to avoid a pass-through list in a simple interpolation
+	if err := result.SetType(types.TypeStr); err != nil {
+		return nil, errwrap.Wrapf(err, "interpolated string expected a different type")
+	}
 	return result, nil // replacement
 }
 

lang/interpolate/interpolate_test.go

@@ -41,6 +41,7 @@ import (
 	"github.com/purpleidea/mgmt/lang/funcs"
 	"github.com/purpleidea/mgmt/lang/interfaces"
 	"github.com/purpleidea/mgmt/lang/parser"
+	"github.com/purpleidea/mgmt/lang/types"
 	"github.com/purpleidea/mgmt/util"
 
 	"github.com/davecgh/go-spew/spew"
@@ -384,6 +385,9 @@ func TestInterpolateBasicStmt(t *testing.T) {
 				},
 			},
 		}
+		if err := resName.SetType(types.TypeStr); err != nil {
+			panic("could not set type")
+		}
 		exp := &ast.StmtProg{
 			Body: []interfaces.Stmt{
 				&ast.StmtRes{
@@ -574,6 +578,9 @@ func TestInterpolateBasicExpr(t *testing.T) {
 				},
 			},
 		}
+		if err := exp.SetType(types.TypeStr); err != nil {
+			panic("could not set type")
+		}
 		testCases = append(testCases, test{
 			name: "basic expansion",
 			ast:  xast,

lang/interpret_test/TestAstFunc2/unify-interpolate-edge1-fail.txtar

@@ -0,0 +1,10 @@
+-- main.mcl --
+$name = ["a", "bb", "ccc",]
+test $name {}
+test "test" {}
+
+#Test[$name] -> Test["test"]     # must pass
+Test["${name}"] -> Test["test"] # must fail
+
+-- OUTPUT --
+# err: errUnify: can't unify, invariant illogicality with equality: base kind does not match (Str != List)

lang/interpret_test/TestAstFunc2/unify-interpolate-edge1-pass.txtar

@@ -0,0 +1,16 @@
+-- main.mcl --
+$name = ["a", "bb", "ccc",]
+test $name {}
+test "test" {}
+
+Test[$name] -> Test["test"]      # must pass
+#Test["${name}"] -> Test["test"] # must fail
+
+-- OUTPUT --
+Edge: test[a] -> test[test] # test[a] -> test[test]
+Edge: test[bb] -> test[test] # test[bb] -> test[test]
+Edge: test[ccc] -> test[test] # test[ccc] -> test[test]
+Vertex: test[a]
+Vertex: test[bb]
+Vertex: test[ccc]
+Vertex: test[test]

lang/interpret_test/TestAstFunc2/unify-interpolate-edge2-fail.txtar

@@ -0,0 +1,10 @@
+-- main.mcl --
+$name = ["a", "bb", "ccc",]
+test $name {}
+test "test" {}
+
+#Test["test"] -> Test[$name]    # must pass
+Test["test"] -> Test["${name}"] # must fail
+
+-- OUTPUT --
+# err: errUnify: can't unify, invariant illogicality with equality: base kind does not match (Str != List)

lang/interpret_test/TestAstFunc2/unify-interpolate-edge2-pass.txtar

@@ -0,0 +1,16 @@
+-- main.mcl --
+$name = ["a", "bb", "ccc",]
+test $name {}
+test "test" {}
+
+Test["test"] -> Test[$name]      # must pass
+#Test["test"] -> Test["${name}"] # must fail
+
+-- OUTPUT --
+Edge: test[test] -> test[a] # test[test] -> test[a]
+Edge: test[test] -> test[bb] # test[test] -> test[bb]
+Edge: test[test] -> test[ccc] # test[test] -> test[ccc]
+Vertex: test[a]
+Vertex: test[bb]
+Vertex: test[ccc]
+Vertex: test[test]

lang/interpret_test/TestAstFunc2/unify-interpolate-res-fail.txtar

@@ -0,0 +1,8 @@
+-- main.mcl --
+$name = ["a", "bb", "ccc",]
+
+#test $name {}    # must pass
+test "${name}" {} # must fail
+
+-- OUTPUT --
+# err: errUnify: can't unify, invariant illogicality with equality: base kind does not match (Str != List)

lang/interpret_test/TestAstFunc2/unify-interpolate-res-pass.txtar

@@ -0,0 +1,10 @@
+-- main.mcl --
+$name = ["a", "bb", "ccc",]
+
+test $name {}      # must pass
+#test "${name}" {} # must fail
+
+-- OUTPUT --
+Vertex: test[a]
+Vertex: test[bb]
+Vertex: test[ccc]