refactor: cleaner flow

Author: Luca Bianconi

Diff for: buildcache/build_cache.go

@@ -23,6 +23,25 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
+type wrapError struct {
+	wrapped error
+}
+
+func (e wrapError) Error() string {
+	return e.wrapped.Error()
+}
+
+func (e wrapError) Unwrap() error {
+	return e.wrapped
+}
+
+type ErrCreateBaseDir struct {
+	wrapError
+}
+type ErrWriteLastUsedFile struct {
+	wrapError
+}
+
 const lastUsedFileName = ".last-used"
 
 // BuildCache represents a cache of built files (sketches and cores), it's designed
@@ -37,11 +56,11 @@ type BuildCache struct {
 func (bc *BuildCache) GetOrCreate(key string) (*paths.Path, error) {
 	keyDir := bc.baseDir.Join(key)
 	if err := keyDir.MkdirAll(); err != nil {
-		return nil, err
+		return nil, &ErrCreateBaseDir{wrapError{err}}
 	}
 
 	if err := keyDir.Join(lastUsedFileName).WriteFile([]byte{}); err != nil {
-		return nil, err
+		return nil, &ErrWriteLastUsedFile{wrapError{err}}
 	}
 	return keyDir, nil
 }

Diff for: legacy/builder/phases/core_builder.go

@@ -100,6 +100,10 @@ func compileCore(ctx *types.Context, buildPath *paths.Path, buildCachePath *path
 		targetArchivedCore = buildCachePath.Join(archivedCoreName, "core.a")
 		_, buildCacheErr = buildcache.New(buildCachePath).GetOrCreate(archivedCoreName)
 
+		if errors.As(buildCacheErr, &buildcache.ErrCreateBaseDir{}) {
+			return nil, nil, fmt.Errorf(tr("creating core cache folder: %s", err))
+		}
+
 		canUseArchivedCore := !ctx.OnlyUpdateCompilationDatabase &&
 			!ctx.Clean &&
 			!builder_utils.CoreOrReferencedCoreHasChanged(realCoreFolder, targetCoreFolder, targetArchivedCore)
@@ -125,11 +129,6 @@ func compileCore(ctx *types.Context, buildPath *paths.Path, buildCachePath *path
 
 	// archive core.a
 	if targetArchivedCore != nil && !ctx.OnlyUpdateCompilationDatabase {
-		if buildCacheErr != nil {
-			if err := targetArchivedCore.Parent().Mkdir(); err != nil {
-				return nil, nil, fmt.Errorf(tr("creating core cache folder: %s", err))
-			}
-		}
 		err := archiveFile.CopyTo(targetArchivedCore)
 		if ctx.Verbose {
 			if err == nil {