detect conflict with multiple mounts

loader/validate.go

@@ -172,6 +172,24 @@ func checkConsistency(project *types.Project) error { //nolint:gocyclo
 				}
 			}
 		}
+
+		mounts := map[string]string{}
+		for i, tmpfs := range s.Tmpfs {
+			loc := fmt.Sprintf("services.%s.tmpfs[%d]", s.Name, i)
+			path, _, _ := strings.Cut(tmpfs, ":")
+			if p, ok := mounts[path]; ok {
+				return fmt.Errorf("%s: target %s already mounted as %s", loc, path, p)
+			}
+			mounts[path] = loc
+		}
+		for i, volume := range s.Volumes {
+			loc := fmt.Sprintf("services.%s.volumes[%d]", s.Name, i)
+			if p, ok := mounts[volume.Target]; ok {
+				return fmt.Errorf("%s: target %s already mounted as %s", loc, volume.Target, p)
+			}
+			mounts[volume.Target] = loc
+		}
+
 	}
 
 	for name, secret := range project.Secrets {

loader/validate_test.go

@@ -407,3 +407,32 @@ func TestValidateWatch(t *testing.T) {
 		assert.ErrorContains(t, err, "depends on undefined service")
 	})
 }
+
+func TestValidateMountConflict(t *testing.T) {
+	project := &types.Project{
+		Services: types.Services{
+			"myservice": {
+				Name:  "myservice",
+				Image: "scratch",
+				Tmpfs: []string{
+					"/foo",
+					"/conflict:size=64m",
+				},
+				Volumes: []types.ServiceVolumeConfig{
+					{
+						Type:   "bind",
+						Target: "/bar",
+						Source: ".",
+					},
+					{
+						Type:   "bind",
+						Target: "/conflict",
+						Source: ".",
+					},
+				},
+			},
+		},
+	}
+	err := checkConsistency(project)
+	assert.Error(t, err, "services.myservice.volumes[1]: target /conflict already mounted as services.myservice.tmpfs[1]")
+}