[GitHub] [mynewt-newt] ccollins476ad opened a new pull request #312: Use "detached head" instead of local branches

[GitBox <gi...@apache.org>]

ccollins476ad opened a new pull request #312: Use "detached head" instead of local branches
URL: https://github.com/apache/mynewt-newt/pull/312
 
 
   ## SUMMARY
   
   This PR changes how newt interacts with git.  Newt used to use a mix of "detached head" and local branches.  With this PR, newt uses "detached head" exclusively.
   
   ## OLD BEHAVIOR
   
   Newt used a combination of "detached head" and local branches.
   
   * When upgrading to a version mapped to a branch, newt would check out a local branch with the appropriate name.  For example, when upgrading to 0.0.0, newt would check out a local "master" branch.
   
   * When upgrading to a version mapped to a tag or a commit hash, newt would put the repo in a "detached head" state.
   
   This inconsistency comes from the `git checkout` command.  Git puts a repo in a different state depending on the type of commit being checked out.
   
   ## NEW BEHAVIOR
   
   Newt uses "detached head" exclusively.  When upgrading to a version mapped to a branch or tag, newt looks up the corresponding commit hash and checks it out.
   
   In addition, this PR adds a clarification in semantics:
   
   > Only the following commands make modifications to git repos:
   > * new
   > * install
   > * upgrade
   > * info -r
   > 
   > All other commands leave the git repos untouched.  E.g., they do not run `git fetch`, `git checkout`, or `git remote set-url`.
   
   This change simplifies working with custom branches.
   
   ## IMPROVEMENTS
   
   This change improves newt in several ways:
   
   1. Lower chance of git conflicts.  When newt used local branches, there was always a chance of pulling incompatible commits into an existing branch.  This was especially likely when using `newt sync` and changing a repo's remote URL.
   
   2. No need for the `newt sync` command.  The sync command was only necessary due to newt's use of local branches.  Now, `newt upgrade` alone does the right thing: it fetches from `origin` and checks out the correct commit.  For branch-backed versions, newt checks out the latest
   commit in the branch.
   
   The `newt sync` command has been deprecated.  Now it prints a warning message and performs a `newt upgrade`.
   
   3. Proper support for branches and tags in `project.yml`.  Newt has always allowed the `<hash>-commit` notation for a repo version string, but it did not correctly handle `<branch>-commit` or `<tag>-commit`.  Now these version strings work correctly.
   
   ## NOTES
   
   In my opinion, we should think about deprecating `newt install`.  This command doesn't seem very useful; just use `newt upgrade`.

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