acc: handle EnvMatrix overrides (#2578)

## Changes
Handle EnvMatrix overrides in tests.

Implement transformer for mergo. Introducing a new type like EnvMatrix
and only overriding behavior for that type doesn't seem to be possible
because `tool` doesn't support `inline` declaration.

## Tests
Add self-tests

Author: kanterov

acceptance/internal/config.go

@@ -3,6 +3,7 @@ package internal
 import (
 	"os"
 	"path/filepath"
+	"reflect"
 	"slices"
 	"sort"
 	"strings"
@@ -145,7 +146,14 @@ func LoadConfig(t *testing.T, dir string) (TestConfig, string) {
 
 	for _, cfgName := range configs[1:] {
 		cfg := DoLoadConfig(t, cfgName)
-		err := mergo.Merge(&result, cfg, mergo.WithOverride, mergo.WithoutDereference, mergo.WithAppendSlice)
+		err := mergo.Merge(
+			&result,
+			cfg,
+			mergo.WithOverride,
+			mergo.WithoutDereference,
+			mergo.WithAppendSlice,
+			mergo.WithTransformers(mapTransformer{}),
+		)
 		if err != nil {
 			t.Fatalf("Error during config merge: %s: %s", cfgName, err)
 		}
@@ -174,6 +182,27 @@ func DoLoadConfig(t *testing.T, path string) TestConfig {
 	return config
 }
 
+// mapTransformer is a mergo transformer that merges two maps
+// by overriding values in the destination map with values from the source map.
+//
+// In our case, source map is located in test directory, and destination map is located
+// in a parent directory.
+type mapTransformer struct{}
+
+func (t mapTransformer) Transformer(typ reflect.Type) func(dst, src reflect.Value) error {
+	if typ.Kind() == reflect.Map {
+		return func(dst, src reflect.Value) error {
+			if dst.IsNil() {
+				dst.Set(reflect.MakeMap(typ))
+			}
+
+			return mergo.Merge(dst.Addr().Interface(), src.Interface(), mergo.WithOverride)
+		}
+	}
+
+	return nil
+}
+
 // This function takes EnvMatrix and expands into a slice of environment configurations.
 // Each environment configuration is a slice of env vars in standard Golang format.
 // For example,

acceptance/selftest/envmatrix/output.txt …ance/selftest/envmatrix/inner/output.txtacceptance/selftest/envmatrix/output.txt renamed to acceptance/selftest/envmatrix/inner/output.txt acceptance/selftest/envmatrix/output.txt renamed to acceptance/selftest/envmatrix/inner/output.txt

@@ -1,2 +1,3 @@
 FIRST=[FIRST]
 SECOND=[SECOND]
+THIRD=[THIRD]

acceptance/selftest/envmatrix/inner/script

@@ -0,0 +1,7 @@
+[ "$FIRST" = "one" ] || [ "$FIRST" = "two" ]
+[ "$SECOND" = "variantA" ] || [ "$SECOND" = "variantB" ]
+[ "$THIRD" = "three" ]
+
+echo "FIRST=$FIRST"
+echo "SECOND=$SECOND"
+echo "THIRD=$THIRD"

acceptance/selftest/envmatrix/inner/test.toml

@@ -0,0 +1,3 @@
+[EnvMatrix]
+FIRST = ["one", "two"]
+SECOND = ["variantA", "variantB"]

acceptance/selftest/envmatrix/script

@@ -1,3 +1,3 @@
 [EnvMatrix]
-FIRST = ["one", "two"]
-SECOND = ["variantA", "variantB"]
+FIRST = ["overriden-in-inner"]
+THIRD = ["three"]