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The status command is used to provide a pithy listing of the changes between
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two trees. Its common case is between the working tree and the basis tree, but
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it can be used between any two arbitrary trees.
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Status shows several things in parallel (for the paths the user supplied mapped
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across the from and to tree, and any pending merges in the to tree).
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1. Single line summary of all new revisions - the pending merges and their
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2. Changes to the tree shape - adds/deletes/renames.
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3. Changes to versioned content - kind changes and content changes.
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4. Unknown files in the to tree.
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5. Files with conflicts in the to tree.
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Ideal work for working tree to historical status
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------------------------------------------------
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We need to do the following things at a minimum:
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1. Determine new revisions - the pending merges and history.
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1. Retrieve the first line of the commit message for the new revisions.
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1. Determine the tree differences between the two trees using the users paths
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to limit the scope, and resolving paths in the trees for any pending merges.
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We arguably don't care about tracking metadata for this - only the value of
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the tree the user commited.
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1. The entire contents of directories which are versioned when showing
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1. Whether a given unversioned path is unknown or ignored.
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1. The list conflicted paths in the tree (which match the users path
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Expanding on the tree difference case we will need to:
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1. Stat every path in working trees which is included by the users path
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selection to ascertain kind and execute bit.
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1. For paths which have the same kind in both trees and have content, read
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that content or otherwise determine whether the content has changed. Using
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our hash cache from the dirstate allows us to avoid reading the file in the
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common case. There are alternative ways to achieve this - we could record
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a pointer to a revision which contained this fileid with the current content
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rather than storing the content's hash; but this seems to be a pointless
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double-indirection unless we save enough storage in the working tree. A
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variation of this is to not record an explicit pointer but instead
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define an implicit pointer as being to the left-hand-parent tree.
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- We should stat files in the same directory without reading or statting
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files in other directories. That is we should do all the statting we
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intend to do within a given directory without doing any other IO, to
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minimise pressure on the drive heads to seek.
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- We should read files in the same directory without reading or writing
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files in other directories - and note this is separate to statting (file
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data is usually physically disjoint to metadata).
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- The stat operation clearly involves every versioned path in the common case.
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- Expanding out the users path selection in a naive manner involves reading the
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entire tree shape information for both trees and for all pending-merge trees.
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(Dirstate makes this tolerably cheap for now, but we're still scaling
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- The amount of effort required to generate tree differences between the
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working tree and the basis tree is interesting: with a tree-like structure
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and some generatable name for child nodes we use the working tree data to
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eliminate accessing or considering subtrees regardless of historival
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age. However, if we have had to access the historical tree shape to
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perform path selection this rather reduces the win we can obtain here.
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If we can cause path expansion to not require historical shape access
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(perhaps by performing the expansion after calculating the tree
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difference for the top level of the selected path) then we can gain a
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larger win. This strongly suggests that path expansion and tree
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difference generation should be linked in terms of API.
added
removed
doc/developers/status.txt
