Struttura `node_modules` con collegamenti simbolici

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This article only describes how pnpm's node_modules are structured when there are no packages with peer dependencies. For the more complex scenario of dependencies with peers, see how peers are resolved.

pnpm's node_modules layout uses symbolic links to create a nested structure of dependencies.

Every file of every package inside node_modules is a hard link to the content-addressable store. Let's say you install foo@1.0.0 that depends on bar@1.0.0. pnpm will hard link both packages to node_modules like this:

node_modules
└── .pnpm
    ├── bar@1.0.0
    │   └── node_modules
    │       └── bar
    │           ├── index.js     -> <store>/001
    │           └── package.json -> <store>/002
    └── foo@1.0.0
        └── node_modules
            └── foo
                ├── index.js     -> <store>/003
                └── package.json -> <store>/004

These are the only "real" files in node_modules. Once all the packages are hard linked to node_modules, symbolic links are created to build the nested dependency graph structure.

As you might have noticed, both packages are hard linked into a subfolder inside a node_modules folder (foo@1.0.0/node_modules/foo). Ciò è necessario per:

1. allow packages to import themselves. foo should be able to require('foo/package.json') or import * as package from "foo/package.json".
2. avoid circular symlinks. Dependencies of packages are placed in the same folder in which the dependent packages are. For Node.js it doesn't make a difference whether dependencies are inside the package's node_modules or in any other node_modules in the parent directories.

La fase successiva dell'installazione è il collegamento simbolico delle dipendenze. bar is going to be symlinked to the foo@1.0.0/node_modules folder:

node_modules
└── .pnpm
    ├── bar@1.0.0
    │   └── node_modules
    │       └── bar -> <store>
    └── foo@1.0.0
        └── node_modules
            ├── foo -> <store>
            └── bar -> ../../bar@1.0.0/node_modules/bar

Successivamente, vengono gestite le dipendenze dirette. foo is going to be symlinked into the root node_modules folder because foo is a dependency of the project:

node_modules
├── foo -> ./.pnpm/foo@1.0.0/node_modules/foo
└── .pnpm
    ├── bar@1.0.0
    │   └── node_modules
    │       └── bar -> <store>
    └── foo@1.0.0
        └── node_modules
            ├── foo -> <store>
            └── bar -> ../../bar@1.0.0/node_modules/bar

Questo è un esempio molto semplice. Tuttavia, il layout manterrà questa struttura indipendentemente dal numero di dipendenze e dalla profondità del grafico delle dipendenze.

Let's add qar@2.0.0 as a dependency of bar and foo. Ecco come apparirà la nuova struttura:

node_modules
├── foo -> ./.pnpm/foo@1.0.0/node_modules/foo
└── .pnpm
    ├── bar@1.0.0
    │   └── node_modules
    │       ├── bar -> <store>
    │       └── qar -> ../../qar@2.0.0/node_modules/qar
    ├── foo@1.0.0
    │   └── node_modules
    │       ├── foo -> <store>
    │       ├── bar -> ../../bar@1.0.0/node_modules/bar
    │       └── qar -> ../../qar@2.0.0/node_modules/qar
    └── qar@2.0.0
        └── node_modules
            └── qar -> <store>

As you may see, even though the graph is deeper now (foo > bar > qar), the directory depth in the file system is still the same.

Questo layout potrebbe sembrare strano a prima vista, ma è completamente compatibile con l'algoritmo di risoluzione del modulo di Node! When resolving modules, Node ignores symlinks, so when bar is required from foo@1.0.0/node_modules/foo/index.js, Node does not use bar at foo@1.0.0/node_modules/bar, but instead, bar is resolved to its real location (bar@1.0.0/node_modules/bar). As a consequence, bar can also resolve its dependencies which are in bar@1.0.0/node_modules.

Un grande bonus di questo layout è che solo i pacchetti che sono davvero nelle dipendenze sono accessibili. With a flattened node_modules structure, all hoisted packages are accessible. To read more about why this is an advantage, see "pnpm's strictness helps to avoid silly bugs"

Unfortunately, many packages in the ecosystem are broken — they use dependencies that are not listed in their package.json. To minimize the number of issues new users encounter, pnpm hoists all dependencies by default into node_modules/.pnpm/node_modules. To disable this hoisting, set hoist to false.