fix: "cannot unmarshal !!str `<no value>` into bool" errors in state templates (#645)

Seems like we are affected by https://github.com/golang/go/issues/24963. That is, even though we internally use the template option `missingkey=zero`, in some cases it still prints `<no value>` instead of zero values, which has been confusing the state yaml parsing.

This fixes the issue by naively replacing all the remaining occurrences of `<no value>` in the rendered text, while printing debug logs to ease debugging in the future when there is unexpected side-effects introduced by this native method.

Fixes #553

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/Masterminds/semver v1.4.1
 	github.com/Masterminds/sprig v2.16.0+incompatible
 	github.com/aokoli/goutils v1.0.1 // indirect
-	github.com/google/go-cmp v0.3.0 // indirect
+	github.com/google/go-cmp v0.3.0
 	github.com/google/uuid v0.0.0-20161128191214-064e2069ce9c // indirect
 	github.com/huandu/xstrings v1.0.0 // indirect
 	github.com/imdario/mergo v0.3.6

pkg/app/app_test.go

@@ -838,7 +838,7 @@ releases:
 	}
 }
 
-func TestVisitDesiredStatesWithReleasesFiltered_StateValueOverrides(t *testing.T) {
+func TestVisitDesiredStatesWithReleasesFiltered_EnvironmentValueOverrides(t *testing.T) {
 	files := map[string]string{
 		"/path/to/helmfile.yaml": `
 environments:

pkg/app/two_pass_renderer.go

@@ -3,6 +3,7 @@ package app
 import (
 	"bytes"
 	"fmt"
+	"github.com/google/go-cmp/cmp"
 	"github.com/roboll/helmfile/pkg/environment"
 	"github.com/roboll/helmfile/pkg/state"
 	"github.com/roboll/helmfile/pkg/tmpl"
@@ -31,10 +32,20 @@ func (r *desiredStateLoader) renderEnvironment(firstPassEnv *environment.Environ
 			return firstPassEnv
 		}
 	}
+	yamlData := yamlBuf.String()
+
+	// Work-around for https://github.com/golang/go/issues/24963
+	sanitized := strings.ReplaceAll(yamlData, "<no value>", "")
+
+	if len(yamlData) != len(sanitized) {
+		msg := "replaced <no value>s to workaround https://github.com/golang/go/issues/24963 to address https://github.com/roboll/helmfile/issues/553:\n%s"
+		r.logger.Debugf(msg, cmp.Diff(yamlData, sanitized))
+	}
+
 	c := r.underlying()
 	c.Strict = false
 	// create preliminary state, as we may have an environment. Tolerate errors.
-	prestate, err := c.ParseAndLoad(yamlBuf.Bytes(), baseDir, filename, r.env, false, firstPassEnv)
+	prestate, err := c.ParseAndLoad([]byte(sanitized), baseDir, filename, r.env, false, firstPassEnv)
 	if err != nil && r.logger != nil {
 		switch err.(type) {
 		case *state.StateLoadError:

pkg/tmpl/context_tmpl.go

@@ -13,9 +13,9 @@ func (c *Context) stringTemplate() *template.Template {
 	}
 	tmpl := template.New("stringTemplate").Funcs(funcMap)
 	if c.preRender {
-		tmpl.Option("missingkey=zero")
+		tmpl = tmpl.Option("missingkey=zero")
 	} else {
-		tmpl.Option("missingkey=error")
+		tmpl = tmpl.Option("missingkey=error")
 	}
 	return tmpl
 }