Added support for inheritance in importing repository files.

README.md

@@ -90,6 +90,168 @@ The `import` command also supports input in the [rosinstall file format](http://
 
 Only for this command vcs2l supports the pseudo clients `tar` and `zip` which fetch a tarball / zipfile from a URL and unpack its content. For those two types the `version` key is optional. If specified only entries from the archive which are in the subfolder specified by the version value are being extracted.
 
+### Import with extends functionality
+
+The `vcs import` command supports an `extends` key at the top level of the YAML file. The value of that key is a path or URL to another YAML file which is imported first.
+This base file can itself also contain the key to chain multiple files. The extension to this base file is given precedence over the parent in case of duplicate repository entries.
+
+#### Normal Extension
+
+For instance, consider the following two files:
+
+- **`base.repos`**: contains three repositories `vcs2l`, `immutable/hash` and `immutable/tag`, checked out at specific versions.
+
+   ```yaml
+   ---
+   repositories:
+     vcs2l:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: main
+     immutable/hash:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 377d5b3d03c212f015cc832fdb368f4534d0d583
+     immutable/tag:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.3
+   ```
+
+- **`base_extension.repos`**: extends the base file and overrides the version of `immutable/hash` and `immutable/tag` repositories.
+
+   ```yaml
+   ---
+   extends: base.repos
+   repositories:
+     immutable/hash:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 25e4ae2f1dd28b0efcd656f4b1c9679d8a7d6c22
+     immutable/tag:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.5
+   ```
+The resulting extension import would import vcs2l at version `main`, `immutable/hash` at version `25e4ae2` and `immutable/tag` at version `1.1.5`.
+
+#### Multiple Extensions
+
+The `extends` key also supports a list of files to extend from. The files are imported in the order they are specified and the precedence is given to the last file in case of duplicate repository entries.
+
+For instance, consider the following three files:
+
+- **`base_1.repos`**: contains two repositories `vcs2l` and `immutable/hash`, checked out at `1.1.3`.
+
+   ```yaml
+   ---
+   repositories:
+    immutable/hash:
+      type: git
+      url: https://github.com/ros-infrastructure/vcs2l.git
+      version: e700793cb2b8d25ce83a611561bd167293fd66eb  # 1.1.3
+     vcs2l:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.3
+    ```
+
+- **`base_2.repos`**: contains two repositories `vcs2l` and `immutable/hash`, checked out at `1.1.4`.
+
+   ```yaml
+   ---
+   repositories:
+    immutable/hash:
+      type: git
+      url: https://github.com/ros-infrastructure/vcs2l.git
+      version: 2c7ff89d12d8a77c36b60d1f7ba3039cdd3f742b  # 1.1.4
+     vcs2l:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.4
+  ```
+
+- **`multiple_extension.repos`**: extends both base files and overrides the version of `vcs2l` repository.
+
+   ```yaml
+   ---
+   extends:
+     - base_1.repos  # Lower priority
+     - base_2.repos # Higher priority
+   repositories:
+     vcs2l:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.5
+   ```
+
+The resulting extension import would import `immutable/hash` at version `1.1.4` (from `base_2.repos`) and `vcs2l` at version `1.1.5`.
+
+Duplicate file names in the `extends` list are not allowed and would raise the following error:
+
+```bash
+Duplicate entries found in extends in file: <relative-path>/multiple_extension.repos
+```
+
+#### Circular Loop Protection
+
+In order to avoid infinite loops in case of circular imports the tool detects already imported files and raises an error if such a file is encountered again.
+
+For instance, consider the following two files:
+
+- **`loop_base.repos`**: extends the `loop_extension.repos` file, and contains two repositories `vcs2l` and `immutable/tag`.
+
+   ```yaml
+   ---
+   extends: loop_extension.repos
+   repositories:
+     vcs2l:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: main
+     immutable/tag:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.3
+   ```
+
+- **`loop_extension.repos`**: extends the `loop_base.repos` file, and modifies the version of `immutable/tag` with `1.1.5`.
+
+   ```yaml
+   ---
+   extends: loop_base.repos
+   repositories:
+     immutable/tag:
+       type: git
+       url: https://github.com/ros-infrastructure/vcs2l.git
+       version: 1.1.5
+   ```
+The resulting extension import would prevent the download and raise the following error:
+
+```bash
+Circular import detected: <relative-path>/loop_extension.repos
+```
+
+#### File path behaviour
+
+Currently there are two ways to specify the path to the repository file passed to `vcs import`:
+
+1. **Recommended**: Using `--input`.
+
+   * For instance: `vcs import --input my.repos <destination-path>`
+
+   * The extended files are searched relative to the location of `my.repos`.
+
+   * You do not require to be in the same directory as `my.repos` to run the command.
+
+2. Using the input redirection operator `<` to pass a local file path via `stdin`.
+
+   * For instance: `vcs import < my.repos <destination-path>`
+
+    * The extended files are searched relative to the current working directory.
+
+    * Therefore, you have to be in the **same** directory as `my.repos` to run the command. In addition, all the extended files must also be relative to the current working directory.
+
 ### Delete set of repositories
 
 The `vcs delete` command removes all directories of repositories which are passed in via `stdin` in YAML format.

test/import_extends.txt

@@ -0,0 +1,67 @@
+......
+=== ./immutable/hash (git) ===
+Cloning into '.'...
+Note: switching to 'e700793cb2b8d25ce83a611561bd167293fd66eb'.
+
+You are in 'detached HEAD' state. You can look around, make experimental
+changes and commit them, and you can discard any commits you make in this
+state without impacting any branches by switching back to a branch.
+
+If you want to create a new branch to retain commits you create, you may
+do so (now or later) by using -c with the switch command. Example:
+
+  git switch -c <new-branch-name>
+
+Or undo this operation with:
+
+  git switch -
+
+Turn off this advice by setting config variable advice.detachedHead to false
+
+HEAD is now at e700793 1.1.3
+=== ./immutable/hash_tar (tar) ===
+Downloaded tarball from 'https://github.com/ros-infrastructure/vcs2l/archive/377d5b3d03c212f015cc832fdb368f4534d0d583.tar.gz' and unpacked it
+=== ./immutable/hash_zip (zip) ===
+Downloaded zipfile from 'https://github.com/ros-infrastructure/vcs2l/archive/377d5b3d03c212f015cc832fdb368f4534d0d583.zip' and unpacked it
+=== ./immutable/tag (git) ===
+Cloning into '.'...
+Note: switching to 'tags/1.1.3'.
+
+You are in 'detached HEAD' state. You can look around, make experimental
+changes and commit them, and you can discard any commits you make in this
+state without impacting any branches by switching back to a branch.
+
+If you want to create a new branch to retain commits you create, you may
+do so (now or later) by using -c with the switch command. Example:
+
+  git switch -c <new-branch-name>
+
+Or undo this operation with:
+
+  git switch -
+
+Turn off this advice by setting config variable advice.detachedHead to false
+
+HEAD is now at e700793 1.1.3
+=== ./vcs2l (git) ===
+Cloning into '.'...
+Note: switching to '1.1.3'.
+
+You are in 'detached HEAD' state. You can look around, make experimental
+changes and commit them, and you can discard any commits you make in this
+state without impacting any branches by switching back to a branch.
+
+If you want to create a new branch to retain commits you create, you may
+do so (now or later) by using -c with the switch command. Example:
+
+  git switch -c <new-branch-name>
+
+Or undo this operation with:
+
+  git switch -
+
+Turn off this advice by setting config variable advice.detachedHead to false
+
+HEAD is now at e700793 1.1.3
+=== ./without_version (git) ===
+Cloning into '.'...

test/import_multiple_extends.txt

@@ -0,0 +1,49 @@
+......
+=== ./immutable/hash (git) ===
+Cloning into '.'...
+Note: switching to '2c7ff89d12d8a77c36b60d1f7ba3039cdd3f742b'.
+
+You are in 'detached HEAD' state. You can look around, make experimental
+changes and commit them, and you can discard any commits you make in this
+state without impacting any branches by switching back to a branch.
+
+If you want to create a new branch to retain commits you create, you may
+do so (now or later) by using -c with the switch command. Example:
+
+  git switch -c <new-branch-name>
+
+Or undo this operation with:
+
+  git switch -
+
+Turn off this advice by setting config variable advice.detachedHead to false
+
+HEAD is now at 2c7ff89 1.1.4
+=== ./immutable/hash_tar (tar) ===
+Downloaded tarball from 'https://github.com/ros-infrastructure/vcs2l/archive/377d5b3d03c212f015cc832fdb368f4534d0d583.tar.gz' and unpacked it
+=== ./immutable/hash_zip (zip) ===
+Downloaded zipfile from 'https://github.com/ros-infrastructure/vcs2l/archive/377d5b3d03c212f015cc832fdb368f4534d0d583.zip' and unpacked it
+=== ./immutable/tag (git) ===
+Cloning into '.'...
+Note: switching to 'tags/1.1.5'.
+
+You are in 'detached HEAD' state. You can look around, make experimental
+changes and commit them, and you can discard any commits you make in this
+state without impacting any branches by switching back to a branch.
+
+If you want to create a new branch to retain commits you create, you may
+do so (now or later) by using -c with the switch command. Example:
+
+  git switch -c <new-branch-name>
+
+Or undo this operation with:
+
+  git switch -
+
+Turn off this advice by setting config variable advice.detachedHead to false
+
+HEAD is now at 25e4ae2 1.1.5
+=== ./vcs2l (git) ===
+Cloning into '.'...
+=== ./without_version (git) ===
+Cloning into '.'...

test/list_extension.repos

@@ -0,0 +1,16 @@
+# Check for hash, tag, and branch imports with extends functionality with predominant tag 1.1.3
+---
+extends: list.repos
+repositories:
+  immutable/hash:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: e700793cb2b8d25ce83a611561bd167293fd66eb  # 1.1.3
+  immutable/tag:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: tags/1.1.3
+  vcs2l:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: 1.1.3

test/list_extension_2.repos

@@ -0,0 +1,16 @@
+# Check for hash, tag, and branch imports with extends functionality with predominant tag 1.1.4
+---
+extends: list.repos
+repositories:
+  immutable/hash:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: 2c7ff89d12d8a77c36b60d1f7ba3039cdd3f742b  # 1.1.4
+  immutable/tag:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: tags/1.1.4
+  vcs2l:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: 1.1.4

test/list_multiple_extension.repos

@@ -0,0 +1,14 @@
+# Check for multiple levels of extension in repositories files.
+---
+extends:
+  - list_extension.repos  # predominant tag is 1.1.3   # Lower priority
+  - list_extension_2.repos # predominant tag is 1.1.4  # Higher priority
+repositories:
+  immutable/tag:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: tags/1.1.5
+  vcs2l:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: main

test/loop_base.repos

@@ -0,0 +1,12 @@
+# Base repositories file that creates an extends a circular import on its extension implementation.
+---
+extends: loop_extension.repos
+repositories:
+  vcs2l:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: main
+  immutable/tag:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: tags/1.1.3

test/loop_extension.repos

@@ -0,0 +1,8 @@
+# Repositories extension file that creates an extends a circular import on its base.
+---
+extends: loop_base.repos
+repositories:
+  vcs2l:
+    type: git
+    url: https://github.com/ros-infrastructure/vcs2l.git
+    version: 1.1.3