acc: Implement config merge (#2294)

## Changes
Instead of using leaf-most config, all configs from root at
acceptance/test.toml to all intermediate ones to leaf config are merged
into one. Maps are merged, slices are appended, other values are
overridden.

I had to disable caching, because it is tricky when merging is involved
- deep copy is needed. There is performance
impact but currently it is tiny, about 1%.

Also, remove empty root config.

## Tests

Manually checked that inheritance of LocalOnly setting worked for these
tests:

Before - integration tests showed:

```
PASS acceptance.TestAccept/bundle/templates/wrong-url (0.70s)
PASS acceptance.TestAccept/bundle/templates/wrong-path (0.44s)
```

After:

```
SKIP acceptance.TestAccept/bundle/templates/wrong-url (0.00s)
SKIP acceptance.TestAccept/bundle/templates/wrong-path (0.00s)
      acceptance_test.go:216: Disabled via LocalOnly setting in bundle/templates/test.toml, bundle/templates/wrong-path/test.toml (CLOUD_ENV=***)
```

NOTICE

@@ -109,3 +109,8 @@ License - https://github.com/hexops/gotextdiff/blob/main/LICENSE
 https://github.com/BurntSushi/toml
 Copyright (c) 2013 TOML authors
 https://github.com/BurntSushi/toml/blob/master/COPYING
+
+dario.cat/mergo
+Copyright (c) 2013 Dario Castañé. All rights reserved.
+Copyright (c) 2012 The Go Authors. All rights reserved.
+https://github.com/darccio/mergo/blob/master/LICENSE

acceptance/config_test.go

@@ -3,9 +3,11 @@ package acceptance_test
 import (
 	"os"
 	"path/filepath"
-	"sync"
+	"slices"
+	"strings"
 	"testing"
 
+	"dario.cat/mergo"
 	"github.com/BurntSushi/toml"
 	"github.com/databricks/cli/libs/testdiff"
 	"github.com/stretchr/testify/require"
@@ -13,11 +15,6 @@ import (
 
 const configFilename = "test.toml"
 
-var (
-	configCache map[string]TestConfig
-	configMutex sync.Mutex
-)
-
 type TestConfig struct {
 	// Place to describe what's wrong with this test. Does not affect how the test is run.
 	Badness string
@@ -65,58 +62,55 @@ type ServerStub struct {
 	}
 }
 
-// FindConfig finds the closest config file.
-func FindConfig(t *testing.T, dir string) (string, bool) {
-	shared := false
+// FindConfigs finds all the config relevant for this test,
+// ordered from the most outermost (at acceptance/) to current test directory (identified by dir).
+// Argument dir must be a relative path from the root of acceptance tests (<project_root>/acceptance/).
+func FindConfigs(t *testing.T, dir string) []string {
+	configs := []string{}
 	for {
 		path := filepath.Join(dir, configFilename)
 		_, err := os.Stat(path)
 
 		if err == nil {
-			return path, shared
+			configs = append(configs, path)
 		}
 
-		shared = true
-
 		if dir == "" || dir == "." {
 			break
 		}
 
-		if os.IsNotExist(err) {
 		dir = filepath.Dir(dir)
+
+		if err == nil || os.IsNotExist(err) {
 			continue
 		}
 
 		t.Fatalf("Error while reading %s: %s", path, err)
 	}
 
-	t.Fatal("Config not found: " + configFilename)
-	return "", shared
+	slices.Reverse(configs)
+	return configs
 }
 
 // LoadConfig loads the config file. Non-leaf configs are cached.
 func LoadConfig(t *testing.T, dir string) (TestConfig, string) {
-	path, leafConfig := FindConfig(t, dir)
+	configs := FindConfigs(t, dir)
 
-	if leafConfig {
-		return DoLoadConfig(t, path), path
+	if len(configs) == 0 {
+		return TestConfig{}, "(no config)"
 	}
 
-	configMutex.Lock()
-	defer configMutex.Unlock()
+	result := DoLoadConfig(t, configs[0])
 
-	if configCache == nil {
-		configCache = make(map[string]TestConfig)
+	for _, cfgName := range configs[1:] {
+		cfg := DoLoadConfig(t, cfgName)
+		err := mergo.Merge(&result, cfg, mergo.WithOverride, mergo.WithAppendSlice)
+		if err != nil {
+			t.Fatalf("Error during config merge: %s: %s", cfgName, err)
+		}
 	}
 
-	result, ok := configCache[path]
-	if ok {
-		return result, path
-	}
-
-	result = DoLoadConfig(t, path)
-	configCache[path] = result
-	return result, path
+	return result, strings.Join(configs, ", ")
 }
 
 func DoLoadConfig(t *testing.T, path string) TestConfig {

acceptance/test.toml

@@ -1,2 +0,0 @@
-# If test directory nor any of its parents do not have test.toml then this file serves as fallback configuration.
-# The configurations are not merged across parents; the closest one is used fully.

go.mod

@@ -5,6 +5,7 @@ go 1.23
 toolchain go1.23.4
 
 require (
+	dario.cat/mergo v1.0.1 // BSD 3-Clause
 	github.com/BurntSushi/toml v1.4.0 // MIT
 	github.com/Masterminds/semver/v3 v3.3.1 // MIT
 	github.com/briandowns/spinner v1.23.1 // Apache 2.0

go.sum

@@ -5,8 +5,8 @@ cloud.google.com/go/auth/oauth2adapt v0.2.2 h1:+TTV8aXpjeChS9M+aTtN/TjdQnzJvmzKF
 cloud.google.com/go/auth/oauth2adapt v0.2.2/go.mod h1:wcYjgpZI9+Yu7LyYBg4pqSiaRkfEK3GQcpb7C/uyF1Q=
 cloud.google.com/go/compute/metadata v0.3.0 h1:Tz+eQXMEqDIKRsmY3cHTL6FVaynIjX2QxYC4trgAKZc=
 cloud.google.com/go/compute/metadata v0.3.0/go.mod h1:zFmK7XCadkQkj6TtorcaGlCW1hT1fIilQDwofLpJ20k=
-dario.cat/mergo v1.0.0 h1:AGCNq9Evsj31mOgNPcLyXc+4PNABt905YmuqPYYpBWk=
-dario.cat/mergo v1.0.0/go.mod h1:uNxQE+84aUszobStD9th8a29P2fMDhsBdgRYvZOxGmk=
+dario.cat/mergo v1.0.1 h1:Ra4+bf83h2ztPIQYNP99R6m+Y7KfnARDfID+a+vLl4s=
+dario.cat/mergo v1.0.1/go.mod h1:uNxQE+84aUszobStD9th8a29P2fMDhsBdgRYvZOxGmk=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/toml v1.4.0 h1:kuoIxZQy2WRRk1pttg9asf+WVv6tWQuBNVmK8+nqPr0=
 github.com/BurntSushi/toml v1.4.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=