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87ce78615a
- Closes #7633 - Moves `Round_Spec.enso` from published `Standard.Test` into our `test/Tests` project; the `Table_Tests` that depend on it, simply `import enso_dev.Tests`. - Changes the layout of the local libraries directory: - It used to be `root/<namespace>/<name>`. - Now it is `root/<dir>` - the namespace and name are now read from `package.yaml` instead. - Adds the parent directory of the current project to the default `ENSO_LIBRARY_PATH`. - It is treated as a secondary path, so the default `ENSO_HOME/lib` still takes precedence. - This allows projects to reference and load 'sibling' projects easily - the only requirement is for the project to enable `prefer-local-libraries: true` or add the other local project to its edition. The edition resolution logic is **not changed**.
237 lines
10 KiB
Markdown
237 lines
10 KiB
Markdown
---
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layout: developer-doc
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title: Editions
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category: libraries
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tags: [libraries, editions]
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order: 1
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---
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# Editions
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This document describes the concept of Editions.
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<!-- MarkdownTOC levels="2,3" autolink="true" -->
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- [What Is An Edition](#what-is-an-edition)
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- [The Edition File](#the-edition-file)
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- [Repositories](#repositories)
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- [Libraries](#libraries)
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- [Extending the Editions](#extending-the-editions)
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- [An Example Configuration](#an-example-configuration)
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- [Edition Resolution](#edition-resolution)
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- [Updating the Editions](#updating-the-editions)
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- [Library Resolution](#library-resolution)
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<!-- /MarkdownTOC -->
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## What Is An Edition
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An Edition, is in principle, a list of library versions that should be
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compatible with each other. An Edition specifies the engine version and a set of
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library versions that can be used together.
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If a library included in an Edition depends on another library, that other
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library must also be included in that Edition and the version at which it is
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included must be compatible with the library that depends on it. Each Edition
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may only include a single version of each library.
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Thus, when a library is to be installed, its version is uniquely determined by
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the selected Edition. A curated Edition file will guarantee that all libraries
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are compatible which simplifies version resolution - the exact version that is
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specified in the Edition is always used.
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## The Edition File
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The Edition file is a YAML file that can contain the following fields:
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- `engine-version` which should be a semantic versioning string specifying the
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engine version that should be associated with that edition,
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- `repositories` which defines the repositories which are sources of library
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packages, its format is [described below](#repositories),
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- `extends` which can contain a name of another Edition that this Edition
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extends,
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- `libraries` which defines the libraries that this Edition should include, its
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format is [described below](#libraries).
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Every field is optional, but for an Edition file to be valid it must specify at
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least the engine version to be used (either by specifying it directly or
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extending another edition that specifies it).
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### Repositories
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The `repositories` field is a list of repository objects.
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Each object must have:
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- a `name` field which specifies the name under which this repository will be
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referred to in the rest of the file,
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- a `url` field which specifies the URL of the root of that repository.
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The `name` can be any string which only needs to be consistent with the names
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used in the package definitions. The only reserved name is `local`, which is a
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special repository name, as [explained below](#library-resolution).
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### Libraries
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The `libraries` field defines the set of libraries included in the edition.
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Each library is represented by an object that must have:
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- a `name` field which is the fully qualified name of the library (consisting of
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its prefix and the name itself),
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- a `repository` field which specifies which repository this package should be
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downloaded from. The `repository` field should refer to the `name` of one of
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the repositories defined in the edition or to `local`,
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- a `version` field which specifies which exact package version should be used
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when the library is imported; it is normally required, but if the `repository`
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is set to `local`, the version must not be specified as the version will only
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depend on what is available in the local repository,
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- an optional `hash` that can be included to verify the integrity of the
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package.
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The `hash` field is currently not implemented.
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### Extending the Editions
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An edition may extend another one by using the `extends` property specifying the
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name of the edition that is to be extended. Henceforth we will call the edition
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that is being extended 'the parent edition' and the other one 'the local
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edition'.
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The current edition inherits all configuration of the parent edition, but it can
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also override specific settings.
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If the `engine-version` is specified in the current edition, it overrides the
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engine version that was implied from the parent edition.
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If the current edition specifies its libraries, they are added to the set of
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available libraries defined by the parent edition. If the current edition
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defines a library that has the same fully qualified name as a library that was
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already defined in the parent edition, the definition from the current edition
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takes precedence. This is the most important mechanism of extending editions
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that allows to override library settings.
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The libraries defined in the current edition can refer to the repositories
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defined both in the current edition and in the parent. However, if the current
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edition defines a repository with the same name as some repository defined in
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the parent edition, the definition from the current edition takes precedence for
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the package definitions of the current definition, **but** the package
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definitions in the parent edition are not affected (they still refer to the
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definition from the their own edition). So you can shadow a repository name, but
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you cannot override it for libraries from the parent edition - instead libraries
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whose repository should be changed must all be overridden in the current
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edition.
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Extending editions can be arbitrarily nested. That is, an edition can extend
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another edition that extends another one etc. The only limitation is that
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obviously there can be no cycles in the chain of extensions. Multiple extensions
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are resolved as follows: first the parent edition is completely resolved (which
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may recursively need to first resolve its parents etc.) and only then the
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current edition applies its overrides.
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### An Example Configuration
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```yaml
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extends: 2021.4
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engine-version: 1.2.3
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repositories:
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- name: secondary
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url: https://example.com/
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libraries:
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- name: Foo.Bar
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version: 1.0.0
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repository: secondary
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```
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The edition file shown above extends a base edition file called `2021.4`. It
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overrides the engine version set in the parent edition to `1.2.3`. Moreover it
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adds a library `Foo.Bar` from the `secondary` repository, or if `2021.4`
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included the library `Foo.Bar`, its definition is overridden with the one
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provided here.
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## Edition Resolution
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The edition configuration for a project is loaded from the `edition` section in
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its `package.yaml` configuration. This 'per-project' edition has no assigned
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names, but it can refer to other editions by their names (when extending them).
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These editions are resolved using the logic below:
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1. Each `<edition-name>` corresponds to a file `<edition-name>.yaml`.
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2. First, the custom edition search paths are scanned for a matching edition
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file. These paths can be defined by the `ENSO_EDITION_PATH` environment
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variable. If it is not defined, it defaults to `<ENSO_HOME>/editions`.
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3. If none is found above, the cached/bundled edition search paths are checked.
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These consist of the directory `$ENSO_DATA_DIRECTORY/editions`, `editions`
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directories in installed engines and the `editions` directory in the
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currently running engine.
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By default, downloaded editions are downloaded to
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`$ENSO_DATA_DIRECTORY/editions`, but also editions bundled with any available
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engines can be loaded.
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See [The Enso Distribution](../distribution/distribution.md) for definitions of
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the directories.
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### Updating the Editions
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The global user configuration file should contain a list of URLs specifying
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edition providers that should be used. By default (if the field is missing), it
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will default to our official edition provider, but users may add other providers
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or remove the official one.
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When `enso update-editions` is called or when requested by the IDE, these
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providers are queried and any new edition files are downloaded to the
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`$ENSO_DATA_DIRECTORY/editions` directory. Editions are assumed to be immutable,
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so edition files that already exist on disk are not redownloaded.
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## Library Resolution
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Below are listed the steps that are taken when resolving an import of library
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`Foo.Bar`:
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1. If and only if the project has `prefer-local-libraries` set to `true`, the
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library path is searched for sub-directories containing Enso packages. If any
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of such packages has a `package.yaml` that defines `namespace:Foo` and
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`name: Bar`, that local instance of the library is chosen. In this particular
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scenario the version check is skipped - whatever version is present in the
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local library path is used.
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2. Otherwise, the list of libraries defined directly in the `edition` section of
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`package.yaml` of the current project is checked, and if the library is
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defined there, it is selected.
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3. Otherwise, any parent editions are consulted; if they too do not contain the
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library that we are searching for, an error is reported.
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4. Once we know the library version to be used:
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1. If the repository associated with the library is `local`, the local
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library path is searched for the first directory to contain the requested
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library and this path is loaded. If the library is not present on the
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library path, an error is reported.
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2. Otherwise, the edition must have defined an exact `<version>` of the
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library that is supposed to be used.
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3. If the library is already downloaded in the local repository cache (the
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directory `$ENSO_DATA_DIRECTORY/lib/Foo/Bar/<version>` exists), that
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package is loaded.
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4. Otherwise, the library is missing and must be downloaded from its
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associated repository (and placed in the cache as above).
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By default, the local library path consists of two directories:
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- `<ENSO_HOME>/libraries/`,
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- the parent directory of the currently opened project.
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This allows the user to access libraries that are placed next to the current
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project (although ones located in the Enso home still take precedence). Still,
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to access local libraries they either have to be defined in the edition, or the
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`prefer-local-libraries` flag must be set to `true`.
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The local library search path can be overridden by setting the
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`ENSO_LIBRARY_PATH` environment variable. It may include a list of directories
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(separated by the system specific path separator); the first directory on the
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list has the highest precedence. If the environment variable is defined, it
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overrides the default paths.
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If `prefer-local-libraries` is `false`, and the edition does not define a
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library at all, when trying to resolve such a library, it is reported as not
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found even if a local version of it exists. That is because auto-discovery of
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local libraries is only done with `prefer-local-libraries` set to `true`. In all
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other cases, the `local` repository overrides should be set explicitly.
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