I got this in my bitbucket pipeline:

pipelines:
  branches:
    develop:
    - step:
        caches:
          - composer
        name: unit tests - Delivery 
        image: totersapp/laravel-docker:phpredis
        script:
        - echo "memory_limit=512M" > /usr/local/etc/php/conf.d/memory-limit-php.ini
        - ln -f -s .env.pipelines .env
        - composer install 
        services:
        - postgres
        - redis

every time it run it is downloading the same files (even on the second run).. any ideas why?

This is the log for composer install:

+ composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Package operations: 199 installs, 0 updates, 0 removals
  - Installing kylekatarnls/update-helper (1.2.0): Downloading (connecting...)Downloading (0%)           Downloading (100%)
  - Installing ocramius/package-versions (1.4.2): Downloading (connecting...)Downloading (0%)           Downloading (30%)Downloading (35%)Downloading (65%)Downloading (95%)Downloading (100%)
  - Installing symfony/polyfill-ctype (v1.13.1): Downloading (connecting...)Downloading (0%)           Downloading (100%)

update: couldn’t override default

Based on this answer I tried this:

- step:
    caches:
      - composer
    image: totersapp/laravel-docker:phpredis
    script:
    - composer install 
..
definitions:
caches:
  composer: /composer/cache

My problem is that I’m trying to call composer with a custom cache directory (in this case it’s /composer/cache) but then again I don’t have a way to call the composer install command while supplying the custom cache directory as an option (ie which is what the bitbucket tutorial is doing with bundle in this example:

 - bundle install --path vendor/bundle

said another way, I cannot run something like this:

- composer install --cache-directory /composer/cache

Update 2: discrepancy between composer.json and composer.lock

• First as a sanity check, I simply cloned the repo of Nico
  Haase, and ran the pipelines, passed ✅
• I copied and pasted the contents of his bitbucket-pipelines.yml into mine, and I copied and pasted his composer.json, I ran the pipeline. Failed ❌

But I got this in the composer install log:

+ composer install --ignore-platform-reqs --no-scripts
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them.
Package operations: 199 installs, 0 updates, 0 removals
  - Installing kylekatarnls/update-helper (1.2.0): Downloading (connecting...)Downloading (0%)           Downloading (100%)
  - Installing ocramius/package-versions (1.4.2): Downloading (connecting...)Downloading (0%)           Downloading (30%)Downloading (35%)Downloading (65%)Downloading (95%)Downloading (100%)
  - Installing symfony/polyfill-ctype (v1.13.1): Downloading (connecting...)Downloading (0%)           Downloading (100%)

• So i figured it’s b/c the composer.lock file is out of sync with composer.json, so I added composer update to my pipeline.. this loaded from cache! ✅but failed here ❌:

    composer update
    Loading composer repositories with package information
    Updating dependencies (including require-dev)
    Package operations: 108 installs, 0 updates, 0 removals
      - Installing ocramius/package-versions (1.4.2): Downloading (connecting...)Downloading (0%)           Downloading (30%)Downloading (35%)Downloading (65%)Downloading (80%)Downloading (100%)
      - Installing symfony/flex (v1.6.0): Downloading (connecting...)Downloading (100%)         
    Symfony operations: 1 recipe (4c6f09f5995a77b64f54dd80675d3bfe)
      - Configuring symfony/flex (>=1.0): From github.com/symfony/recipes:master
    Loading composer repositories with package information
    Updating dependencies (including require-dev)
    Restricting packages listed in "symfony/symfony" to "5.0.*"
    Prefetching 106 packages 
      - Downloading (0%) (5%) (10%) (16%) (21%) (31%) (36%) (41%) (47%) (52%) (57%) (65%) (70%) (75%) (80%) (85%) (90%) (95%) (100%)
    Package operations: 106 installs, 0 updates, 0 removals
      - Installing psr/container (1.0.0): Loading from cache
      - Installing symfony/service-contracts (v2.0.1): Loading from cache
      ..
      ..
    Executing script cache:clear [KO]
     [KO]
    Script cache:clear returned with error code 1
    !!  Fatal Error: composer.lock was created for PHP version 7.2.9 or higher but the current PHP version is 7.1.32.

note: in my original composer.json file, i found this line

  "config": {
        ..
        "cache-dir": "~/.cache/composer",
    },

so I removed that line, but that didn’t help either.

Still digging (for the record this is what my composer.json looks like, i kept the cache-dir part in it for reference)