fix: validate that tags, ldflags, and buildmode, are not provided twice

internal/builders/golang/build.go

@@ -1,6 +1,7 @@
 package golang
 
 import (
+	"errors"
 	"fmt"
 	"go/ast"
 	"go/parser"
@@ -237,6 +238,12 @@ func withOverrides(ctx *context.Context, build config.Build, options api.Options
 func buildGoBuildLine(ctx *context.Context, build config.Build, details config.BuildDetails, options api.Options, artifact *artifact.Artifact, env []string) ([]string, error) {
 	cmd := []string{build.GoBinary, build.Command}
 
+	// tags, ldflags, and buildmode, can only appear once
+	err := validateUniqueFlags(details)
+	if err != nil {
+		return cmd, err
+	}
+
 	flags, err := processFlags(ctx, artifact, env, details.Flags, "")
 	if err != nil {
 		return cmd, err
@@ -283,6 +290,21 @@ func buildGoBuildLine(ctx *context.Context, build config.Build, details config.B
 	return cmd, nil
 }
 
+func validateUniqueFlags(details config.BuildDetails) error {
+	for _, flag := range details.Flags {
+		if strings.HasPrefix(flag, "-tags") && len(details.Tags) > 0 {
+			return errors.New("tags is defined multiple times")
+		}
+		if strings.HasPrefix(flag, "-ldflags") && len(details.Ldflags) > 0 {
+			return errors.New("ldflags is defined multiple times")
+		}
+		if strings.HasPrefix(flag, "-buildmode") && details.Buildmode != "" {
+			return errors.New("buildmode is defined multiple times")
+		}
+	}
+	return nil
+}
+
 func processFlags(ctx *context.Context, a *artifact.Artifact, env, flags []string, flagPrefix string) ([]string, error) {
 	processed := make([]string, 0, len(flags))
 	for _, rawFlag := range flags {

internal/builders/golang/build_test.go

@@ -606,6 +606,34 @@ func TestBuildFailed(t *testing.T) {
 	require.Empty(t, ctx.Artifacts.List())
 }
 
+func TestBuildWithMultipleFlagsFails(t *testing.T) {
+	folder := testlib.Mktmp(t)
+	writeGoodMain(t, folder)
+	config := config.Project{
+		Builds: []config.Build{
+			{
+				ID: "buildid",
+				BuildDetails: config.BuildDetails{
+					Flags: []string{"-tags=test"},
+					Tags:  []string{"xyz"},
+				},
+				Targets: []string{
+					runtimeTarget,
+				},
+				GoBinary: "go",
+				Command:  "build",
+			},
+		},
+	}
+	ctx := context.New(config)
+	ctx.Git.CurrentTag = "5.6.7"
+	err := Default.Build(ctx, ctx.Config.Builds[0], api.Options{
+		Target: "darwin_amd64",
+	})
+	assertContainsError(t, err, `tags is defined multiple times`)
+	require.Empty(t, ctx.Artifacts.List())
+}
+
 func TestRunInvalidAsmflags(t *testing.T) {
 	folder := testlib.Mktmp(t)
 	writeGoodMain(t, folder)