Translate CocoPy subscripts

This change implements simple index-based CocoPy subscripts (and
not the more fully featured slicing ones).

Alongside this, we relax a binder-time check that all dynamic
access types must be strings.  The eval code already handles
numeric (array) accesses, so we will permit these to flow through.

pkg/compiler/binder/stmtexpr.go

@@ -3,6 +3,7 @@
 package binder
 
 import (
+	"fmt"
 	"reflect"
 
 	"github.com/pulumi/coconut/pkg/compiler/ast"
@@ -240,10 +241,25 @@ func (a *astBinder) checkForStatement(node *ast.ForStatement) {
 
 // Expressions
 
-func (a *astBinder) checkExprType(expr ast.Expression, expect symbols.Type) bool {
+func (a *astBinder) checkExprType(expr ast.Expression, expect symbols.Type, alts ...symbols.Type) bool {
 	actual := a.b.ctx.RequireType(expr)
-	if !types.CanConvert(actual, expect) {
-		a.b.Diag().Errorf(errors.ErrorIncorrectExprType.At(expr), expect, actual)
+	conv := false
+	if conv = types.CanConvert(actual, expect); !conv {
+		// If the primary didn't convert, check the alternatives.
+		for _, alt := range alts {
+			if conv = types.CanConvert(actual, alt); conv {
+				break
+			}
+		}
+	}
+	if !conv {
+		expects := expect.Token().String()
+		if len(alts) > 0 {
+			for _, alt := range alts {
+				expects += fmt.Sprintf(" or %v", alt.Token())
+			}
+		}
+		a.b.Diag().Errorf(errors.ErrorIncorrectExprType.At(expr), expects, actual)
 		return false
 	}
 	return true
@@ -382,8 +398,8 @@ func (a *astBinder) checkLoadLocationExpression(node *ast.LoadLocationExpression
 }
 
 func (a *astBinder) checkLoadDynamicExpression(node *ast.LoadDynamicExpression) {
-	// Ensure that the name is either a string or a dynamic.
-	a.checkExprType(node.Name, types.String)
+	// Ensure that the name is either a string, number, or a dynamic.
+	a.checkExprType(node.Name, types.String, types.Number)
 
 	// No matter the outcome, a load dynamic always produces a dynamically typed thing.
 	a.b.ctx.RegisterType(node, types.Dynamic)

pkg/eval/eval.go

@@ -1586,8 +1586,8 @@ func (e *evaluator) evalNew(node diag.Diagable, t symbols.Type, args *[]*ast.Cal
 		for i, arg := range *args {
 			contract.Assertf(arg.Name != nil, "Expected only named args for new of a record type")
 			id := tokens.ClassMemberName(arg.Name.Ident)
-			contract.Assertf(t.TypeMembers()[id] != nil, "Expected named arg to match a type member")
-			contract.Assertf(t.TypeMembers()[id].Primary(), "Expected named arg to match a primary member")
+			contract.Assertf(t.TypeMembers()[id] != nil, "Expected named arg %v to match a type member", id)
+			contract.Assertf(t.TypeMembers()[id].Primary(), "Expected named arg %v to match a primary member", id)
 			val := argobjs[i]
 			prop := rt.PropertyKey(id)
 			addr := obj.GetPropertyAddr(prop, true, true)

tools/cocopy/cocopy/lib/compiler.py

@@ -580,7 +580,12 @@ class Transformer:
         self.not_yet_implemented(node) # value, ctx
 
     def transform_Subscript(self, node):
-        self.not_yet_implemented(node) # value, slice, ctx
+        obj = self.transform_expr(node.value)
+        if isinstance(node.slice, py_ast.Index):
+            idx = self.transform_expr(node.slice.value)
+        else:
+            assert false, "Unsupported slicing type: {}".format(type(node.slice).__name__)
+        return ast.LoadDynamicExpression(idx, obj, loc=self.loc_from(node))
 
     def transform_Tuple(self, node):
         self.not_yet_implemented(node) # elts, ctx