core: Don't save provider input for non-root module

We only support provider input for the root module. This is already
checked in ProviderInput, but was not checked in SetProviderInput. We
can't actually do anything particularly clever with an invalid call here,
but we will at least generate a WARN log to help with debugging.

Also need to update TestBuiltinEvalContextProviderInput to expect this
new behavior of ignoring input for non-root modules.

terraform/eval_context_builtin.go

@@ -198,6 +198,12 @@ func (ctx *BuiltinEvalContext) ProviderInput(pc addrs.ProviderConfig) map[string
 func (ctx *BuiltinEvalContext) SetProviderInput(pc addrs.ProviderConfig, c map[string]cty.Value) {
 	absProvider := pc.Absolute(ctx.Path())
 
+	if !ctx.Path().IsRoot() {
+		// Only root module provider configurations can have input.
+		log.Printf("[WARN] BuiltinEvalContext: attempt to SetProviderInput for non-root module")
+		return
+	}
+
 	// Save the configuration
 	ctx.ProviderLock.Lock()
 	ctx.ProviderInputConfig[absProvider.String()] = c

terraform/eval_context_builtin_test.go

@@ -28,17 +28,17 @@ func TestBuiltinEvalContextProviderInput(t *testing.T) {
 	expected1 := map[string]cty.Value{"value": cty.StringVal("foo")}
 	ctx1.SetProviderInput(providerAddr, expected1)
 
-	expected2 := map[string]cty.Value{"value": cty.StringVal("bar")}
-	ctx2.SetProviderInput(providerAddr, expected2)
+	try2 := map[string]cty.Value{"value": cty.StringVal("bar")}
+	ctx2.SetProviderInput(providerAddr, try2) // ignored because not a root module
 
 	actual1 := ctx1.ProviderInput(providerAddr)
 	actual2 := ctx2.ProviderInput(providerAddr)
 
 	if !reflect.DeepEqual(actual1, expected1) {
-		t.Fatalf("bad: %#v %#v", actual1, expected1)
+		t.Errorf("wrong result 1\ngot:  %#v\nwant: %#v", actual1, expected1)
 	}
-	if !reflect.DeepEqual(actual2, expected2) {
-		t.Fatalf("bad: %#v %#v", actual2, expected2)
+	if actual2 != nil {
+		t.Errorf("wrong result 2\ngot:  %#v\nwant: %#v", actual2, nil)
 	}
 }