Lots of time is wasted doing string manipulation in contextNormalPath()

[nomcopter]

Expected Behavior

Cache hits should be fast

Actual Behavior

50% of this 20s incremental build is wasted splitting and rejoining strings in contextNormalPath

Steps to Reproduce

Build once using webpack-dev-server and then make a trivial change to a deeply nested module.

Operating System, Node, and NPM dependency versions

Mac OS 10.14.1
Node 10.13.0

  "dependencies": {
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    "apollo-cache": "^1.1.9",
    "apollo-cache-inmemory": "^1.2.2",
    "apollo-client": "^2.3.2",
    "apollo-link": "^1.2.2",
    "apollo-link-http": "^1.5.4",
    "axios": "^0.18.0",
    "bootstrap-sass": "^3.3.7",
    "chroma-js": "^1.3.7",
    "classnames": "^2.2.5",
    "fuse.js": "^3.2.1",
    "graphql": "^0.13.2",
    "history": "^4.7.2",
    "jquery": "^3.3.1",
    "lodash": "^4.17.10",
    "material-design-icons": "^3.0.1",
    "moment": "^2.22.2",
    "moment-timezone": "^0.5.21",
    "mousetrap": "^1.6.2",
    "popper.js": "^1.14.4",
    "prop-types": "^15.6.0",
    "querystring": "^0.2.0",
    "rangy": "^1.3.0",
    "react": "16.5.0",
    "react-adopt": "^0.6.0",
    "react-apollo": "^2.1.4",
    "react-beautiful-dnd": "^7.1.3",
    "react-bootstrap": "^0.32.1",
    "react-datepicker": "^1.5.0",
    "react-dnd": "^4.0.2",
    "react-dnd-html5-backend": "^4.0.2",
    "react-dom": "16.5.0",
    "react-hot-loader": "^4.3.3",
    "react-input-autosize": "^2.2.1",
    "react-overlays": "^0.8.3",
    "react-popper": "^1.0.2",
    "react-redux": "^5.0.7",
    "react-router": "4.2.0",
    "react-router-bootstrap": "0.24.4",
    "react-router-dom": "4.2.2",
    "react-router-redux": "^5.0.0-alpha.9",
    "react-select": "^2.1.0",
    "react-select-plus": "^1.2.0",
    "recompose": "^0.27.1",
    "redux": "^3.7.2",
    "reselect": "^3.0.1",
    "seedrandom": "^2.4.3",
    "shallowequal": "^1.1.0",
    "tslib": "^1.9.2",
    "uuid": "^3.2.1",
    "whatwg-fetch": "^2.0.4",
    "zen-observable-ts": "^0.8.9"
  },
  "devDependencies": {
    "@babel/core": "^7.1.2",
    "@babel/plugin-transform-modules-commonjs": "^7.1.0",
    "@babel/polyfill": "^7.0.0",
    "@babel/preset-env": "^7.1.0",
    "@babel/preset-react": "^7.0.0",
    "@types/autoprefixer": "^6.7.3",
    "@types/chai": "^4.1.7",
    "@types/chroma-js": "^1.3.5",
    "@types/classnames": "^2.2.4",
    "@types/express": "^4.11.1",
    "@types/gapi.auth2": "0.0.47",
    "@types/hard-source-webpack-plugin": "^0.9.0",
    "@types/history": "4.6.2",
    "@types/html-webpack-plugin": "^3.2.0",
    "@types/lodash": "^4.14.109",
    "@types/mini-css-extract-plugin": "^0.2.0",
    "@types/mocha": "^5.2.1",
    "@types/moment-timezone": "^0.5.8",
    "@types/mousetrap": "^1.6.0",
    "@types/node": "^10",
    "@types/optimize-css-assets-webpack-plugin": "^1.3.3",
    "@types/prop-types": "^15.5.6",
    "@types/rangy": "^0.0.32",
    "@types/react": "16.4.13",
    "@types/react-beautiful-dnd": "^6.0.1",
    "@types/react-bootstrap": "0.32.9",
    "@types/react-datepicker": "^1.1.2",
    "@types/react-dom": "^16.0.7",
    "@types/react-input-autosize": "^2.0.0",
    "@types/react-overlays": "^0.8.5",
    "@types/react-redux": "4.4.40",
    "@types/react-router": "^4.0.26",
    "@types/react-router-bootstrap": "^0.24.5",
    "@types/react-router-dom": "^4.2.7",
    "@types/react-router-redux": "^5.0.15",
    "@types/react-select": "^2.0.6",
    "@types/react-test-renderer": "^16.0.1",
    "@types/recompose": "^0.26.1",
    "@types/seedrandom": "^2.4.27",
    "@types/shallowequal": "^0.2.3",
    "@types/uglifyjs-webpack-plugin": "^1.1.0",
    "@types/uuid": "^3.4.3",
    "@types/webpack": "^4.4.17",
    "@types/webpack-dev-server": "^3.1.1",
    "@types/webpack-env": "^1.13.6",
    "autoprefixer": "^8.6.0",
    "awesome-typescript-loader": "^5.0.0",
    "babel-loader": "^8.0.4",
    "chai": "^4.2.0",
    "connect-mongo": "^1.3.2",
    "css-loader": "^0.28.11",
    "csstype": "^2.5.3",
    "csurf": "^1.9.0",
    "dotenv": "^5.0.1",
    "ejs": "^2.6.1",
    "express-session": "^1.15.6",
    "file-loader": "^1.1.11",
    "graphql-tag": "^2.9.2",
    "hard-source-webpack-plugin": "^0.12.0",
    "html-webpack-harddisk-plugin": "^0.2.0",
    "html-webpack-plugin": "^3.2.0",
    "mini-css-extract-plugin": "^0.4.4",
    "mocha": "^5.2.0",
    "node-sass": "^4.10.0",
    "npm-run-all": "^4.1.3",
    "optimize-css-assets-webpack-plugin": "^4.0.2",
    "postcss-loader": "^2.1.5",
    "prettier": "^1.13.4",
    "react-test-renderer": "16.3.2",
    "resolve-url-loader": "^2.3.0",
    "sass-loader": "^7.0.2",
    "source-map-loader": "^0.2.3",
    "style-loader": "^0.21.0",
    "ts-node": "^6.1.0",
    "tslint": "^5.11.0",
    "typescript": "~3.1.3",
    "uglifyjs-webpack-plugin": "^2.0.1",
    "webpack": "4.19.0",
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    "webpack-dev-server": "^3.1.10"
  },