fix: build --single-target when using specific targets (#3381)

When using specific targets in the config, single target becomes
ineffective. This should fix it. This also removes other build options
like gomips, goarm, goamd64, etc, as go will infer them from the current
OS. In theory we should one day support all the GO* flags go build
supports.

cmd/build.go

@@ -165,6 +165,10 @@ func setupBuildSingleTarget(ctx *context.Context) {
 		build := &ctx.Config.Builds[i]
 		build.Goos = []string{goos}
 		build.Goarch = []string{goarch}
+		build.Goarm = nil
+		build.Gomips = nil
+		build.Goamd64 = nil
+		build.Targets = nil
 	}
 }
 

cmd/build_test.go

@@ -278,3 +278,49 @@ func TestBuildFlags(t *testing.T) {
 		})
 	})
 }
+
+func TestBuildSingleTargetWithSpecificTargets(t *testing.T) {
+	ctx := context.New(config.Project{
+		ProjectName: "test",
+		Builds: []config.Build{
+			{
+				Targets: []string{
+					"linux_amd64_v1",
+					"darwin_arm64",
+					"darwin_amd64_v1",
+				},
+			},
+		},
+	})
+
+	t.Setenv("GOOS", "linux")
+	t.Setenv("GOARCH", "amd64")
+	setupBuildSingleTarget(ctx)
+	require.Equal(t, config.Build{
+		Goos:   []string{"linux"},
+		Goarch: []string{"amd64"},
+	}, ctx.Config.Builds[0])
+}
+
+func TestBuildSingleTargetRemoveOtherOptions(t *testing.T) {
+	ctx := context.New(config.Project{
+		ProjectName: "test",
+		Builds: []config.Build{
+			{
+				Goos:    []string{"linux", "darwin"},
+				Goarch:  []string{"amd64", "arm64"},
+				Goamd64: []string{"v1", "v2"},
+				Goarm:   []string{"6"},
+				Gomips:  []string{"anything"},
+			},
+		},
+	})
+
+	t.Setenv("GOOS", "linux")
+	t.Setenv("GOARCH", "amd64")
+	setupBuildSingleTarget(ctx)
+	require.Equal(t, config.Build{
+		Goos:   []string{"linux"},
+		Goarch: []string{"amd64"},
+	}, ctx.Config.Builds[0])
+}