do not return warnings as errors from eval

Warnings alone cannot be returned from eval nodes, since are still
treated as errors.

terraform/context_apply_test.go

@@ -12164,3 +12164,42 @@ func TestContext2Apply_provisionerSensitive(t *testing.T) {
 		t.Errorf("expected hook to be called with %q, but was:\n%s", want, got)
 	}
 }
+
+func TestContext2Apply_warnings(t *testing.T) {
+	m := testModuleInline(t, map[string]string{
+		"main.tf": `
+resource "test_resource" "foo" {
+}`,
+	})
+
+	p := testProvider("test")
+	p.PlanResourceChangeFn = testDiffFn
+
+	p.ApplyResourceChangeFn = func(req providers.ApplyResourceChangeRequest) providers.ApplyResourceChangeResponse {
+		resp := testApplyFn(req)
+
+		resp.Diagnostics = resp.Diagnostics.Append(tfdiags.SimpleWarning("warning"))
+		return resp
+	}
+
+	ctx := testContext2(t, &ContextOpts{
+		Config: m,
+		Providers: map[addrs.Provider]providers.Factory{
+			addrs.NewDefaultProvider("test"): testProviderFuncFixed(p),
+		},
+	})
+
+	if _, diags := ctx.Plan(); diags.HasErrors() {
+		t.Fatalf("plan errors: %s", diags.Err())
+	}
+
+	state, diags := ctx.Apply()
+	if diags.HasErrors() {
+		t.Fatalf("diags: %s", diags.Err())
+	}
+
+	inst := state.ResourceInstance(mustResourceInstanceAddr("test_resource.foo"))
+	if inst == nil {
+		t.Fatal("missing 'test_resource.foo' in state:", state)
+	}
+}

terraform/eval_apply.go

@@ -354,7 +354,17 @@ func (n *EvalApply) Eval(ctx EvalContext) (interface{}, error) {
 		}
 	}
 
+	// we have to drop warning-only diagnostics for now
+	if diags.HasErrors() {
 		return nil, diags.ErrWithWarnings()
+	}
+
+	// log any warnings since we can't return them
+	if e := diags.ErrWithWarnings(); e != nil {
+		log.Printf("[WARN] EvalApply %s: %v", n.Addr, e)
+	}
+
+	return nil, nil
 }
 
 // EvalApplyPre is an EvalNode implementation that does the pre-Apply work
@@ -738,7 +748,17 @@ func (n *EvalApplyProvisioners) apply(ctx EvalContext, provs []*configs.Provisio
 		}
 	}
 
+	// we have to drop warning-only diagnostics for now
+	if diags.HasErrors() {
 		return diags.ErrWithWarnings()
+	}
+
+	// log any warnings since we can't return them
+	if e := diags.ErrWithWarnings(); e != nil {
+		log.Printf("[WARN] EvalApplyProvisioners %s: %v", n.Addr, e)
+	}
+
+	return nil
 }
 
 func (n *EvalApplyProvisioners) evalProvisionerConfig(ctx EvalContext, body hcl.Body, self cty.Value, schema *configschema.Block) (cty.Value, tfdiags.Diagnostics) {