refactor(gazelle): use log for warnings

Change-Id: If9130745f58adfccc86b3bdc9f66ac72c7859568

gazelle/blueprint/builder/bp2bzl/bp2bzl.go

@@ -2,6 +2,7 @@ package bp2bzl
 
 import (
 	"fmt"
+	"log"
 	"strings"
 
 	"github.com/ARM-software/bob-build/gazelle/mapper"
@@ -101,7 +102,7 @@ func (t *Transformer) Transform(expr parser.Expression) bzl.Expr {
 			Op: fmt.Sprintf("%s", e.Operator),
 		}
 	default:
-		fmt.Printf("Unhandled type %#v\n", expr)
+		log.Printf("Unhandled type %#v\n", expr)
 	}
 	return nil
 }

gazelle/mconfig/builder/builder.go

@@ -3,7 +3,6 @@ package builder
 import (
 	"fmt"
 	"log"
-	"os"
 	"reflect"
 	"sort"
 
@@ -45,7 +44,7 @@ func ParseLogic(m *mapper.Mapper, expr interface{}) logic.Expr {
 
 		t, ok := types[rv.Index(0).Interface().(string)]
 		if !ok {
-			fmt.Fprintf(os.Stderr, "WARNING: unsupported expression type: '%v'\n", expr)
+			log.Printf("unsupported expression type: '%v'\n", expr)
 			break
 		}
 		var args []logic.Expr
@@ -66,7 +65,7 @@ func ParseLogic(m *mapper.Mapper, expr interface{}) logic.Expr {
 
 func LiteralExpressionToBzl(expression []interface{}) bzl.Expr {
 	if len(expression) != 2 {
-		fmt.Fprintf(os.Stderr, "WARNING: Cannot convert expression '%v' to value literal\n", expression)
+		log.Printf("Cannot convert expression '%v' to value literal\n", expression)
 		return nil
 	}
 
@@ -79,7 +78,7 @@ func LiteralExpressionToBzl(expression []interface{}) bzl.Expr {
 	case "number":
 		return &bzl.LiteralExpr{Token: fmt.Sprintf("%d", int(expression[1].(float64)))}
 	default:
-		fmt.Fprintf(os.Stderr, "WARNING: Cannot convert expression '%v' to value literal, unknown type\n", expression)
+		log.Printf("Cannot convert expression '%v' to value literal, unknown type\n", expression)
 	}
 	return nil
 }
@@ -102,7 +101,7 @@ func (b *Builder) NewFlagDefaultValue(rel string, c *mparser.ConfigData) *FlagDe
 		for _, conditional := range c.ConditionalDefaults {
 			t := logic.Flatten(ParseLogic(b.m, conditional.Condition))
 			if t == nil {
-				fmt.Fprintf(os.Stderr, "WARNING: unsupported conditional expression: '%v'\n", conditional.Condition)
+				log.Printf("unsupported conditional expression: '%v'\n", conditional.Condition)
 				return nil
 			}
 			l := b.lb.RequestLogicalExpr(rel, t)
@@ -114,7 +113,7 @@ func (b *Builder) NewFlagDefaultValue(rel string, c *mparser.ConfigData) *FlagDe
 	if c.Default != nil {
 		defaultValue = LiteralExpressionToBzl(c.Default)
 		if defaultValue == nil {
-			fmt.Fprintf(os.Stderr, "WARNING: cannot determine literal expression from default: '%v'\n", c.Default)
+			log.Printf("cannot determine literal expression from default: '%v'\n", c.Default)
 			return nil
 		}
 	} else {
@@ -304,7 +303,7 @@ func (b *Builder) Build(args language.GenerateArgs, file interface{}) (result la
 		if build_setting_default != nil {
 			flag.SetAttr("build_setting_default", build_setting_default)
 		} else {
-			fmt.Fprintf(os.Stderr, "WARNING: Could not determine build setting default for %v\n", v.Name)
+			log.Printf("Could not determine build setting default for %v\n", v.Name)
 		}
 
 		// Only bool is supported currently for flag values.