[skip changelog] Let SketchMergeSources return error

This adds an error return value, which is currently always nil. This
prepares for making changes that require returning errors.

Author: matthijskooijman

Diff for: arduino/builder/sketch.go

@@ -216,7 +216,7 @@ func SketchLoad(sketchPath, buildPath string) (*sketch.Sketch, error) {
 }
 
 // SketchMergeSources merges all the source files included in a sketch
-func SketchMergeSources(sketch *sketch.Sketch) (int, string) {
+func SketchMergeSources(sketch *sketch.Sketch) (int, string, error) {
 	lineOffset := 0
 	mergedSource := ""
 
@@ -235,7 +235,7 @@ func SketchMergeSources(sketch *sketch.Sketch) (int, string) {
 		mergedSource += item.GetSourceStr() + "\n"
 	}
 
-	return lineOffset, mergedSource
+	return lineOffset, mergedSource, nil
 }
 
 // SketchCopyAdditionalFiles copies the additional files for a sketch to the

Diff for: arduino/builder/sketch_test.go

@@ -180,7 +180,8 @@ func TestMergeSketchSources(t *testing.T) {
 		t.Fatalf("unable to read golden file %s: %v", mergedPath, err)
 	}
 
-	offset, source := builder.SketchMergeSources(s)
+	offset, source, err := builder.SketchMergeSources(s)
+	require.Nil(t, err)
 	require.Equal(t, 2, offset)
 	require.Equal(t, string(mergedBytes), source)
 }
@@ -191,7 +192,8 @@ func TestMergeSketchSourcesArduinoIncluded(t *testing.T) {
 	require.NotNil(t, s)
 
 	// ensure not to include Arduino.h when it's already there
-	_, source := builder.SketchMergeSources(s)
+	_, source, err := builder.SketchMergeSources(s)
+	require.Nil(t, err)
 	require.Equal(t, 1, strings.Count(source, "<Arduino.h>"))
 }
 

Diff for: legacy/builder/container_merge_copy_sketch_files.go

@@ -29,7 +29,10 @@ func (s *ContainerMergeCopySketchFiles) Run(ctx *types.Context) error {
 	if sk == nil {
 		return i18n.WrapError(errors.New("unable to convert legacy sketch to the new type"))
 	}
-	offset, source := bldr.SketchMergeSources(sk)
+	offset, source, err := bldr.SketchMergeSources(sk)
+	if err != nil {
+		return err
+	}
 	ctx.LineOffset = offset
 	ctx.Source = source