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copies: move from a copy on branchpoint to a copy on write approach...
copies: move from a copy on branchpoint to a copy on write approach Before this changes, any branch points results in a copy of the dictionary containing the copy information. This can be very costly for branchy history with few rename information. Instead, we take a "copy on write" approach. Copying the input data only when we are about to update them. In practice we where already doing the copying in half of these case (because `_chain` makes a copy), so we don't add a significant cost here even in the linear case. However the speed up in branchy case is very significant. Here are some timing on the pypy repository. revision: large amount; added files: large amount; rename small amount; c3b14617fbd7 9ba6ab77fd29 before: ! wall 1.399863 comb 1.400000 user 1.370000 sys 0.030000 (median of 10) after: ! wall 0.766453 comb 0.770000 user 0.750000 sys 0.020000 (median of 11) revision: large amount; added files: small amount; rename small amount; c3b14617fbd7 f650a9b140d2 before: ! wall 1.876748 comb 1.890000 user 1.870000 sys 0.020000 (median of 10) after: ! wall 1.167223 comb 1.170000 user 1.150000 sys 0.020000 (median of 10) revision: large amount; added files: large amount; rename large amount; 08ea3258278e d9fa043f30c0 before: ! wall 0.242457 comb 0.240000 user 0.240000 sys 0.000000 (median of 39) after: ! wall 0.211476 comb 0.210000 user 0.210000 sys 0.000000 (median of 45) revision: small amount; added files: large amount; rename large amount; df6f7a526b60 a83dc6a2d56f before: ! wall 0.013193 comb 0.020000 user 0.020000 sys 0.000000 (median of 224) after: ! wall 0.013290 comb 0.010000 user 0.010000 sys 0.000000 (median of 222) revision: small amount; added files: large amount; rename small amount; 4aa4e1f8e19a 169138063d63 before: ! wall 0.001673 comb 0.000000 user 0.000000 sys 0.000000 (median of 1000) after: ! wall 0.001677 comb 0.000000 user 0.000000 sys 0.000000 (median of 1000) revision: small amount; added files: small amount; rename small amount; 4bc173b045a6 964879152e2e before: ! wall 0.000119 comb 0.000000 user 0.000000 sys 0.000000 (median of 8023) after: ! wall 0.000119 comb 0.000000 user 0.000000 sys 0.000000 (median of 7997) revision: medium amount; added files: large amount; rename medium amount; c95f1ced15f2 2c68e87c3efe before: ! wall 0.201898 comb 0.210000 user 0.200000 sys 0.010000 (median of 48) after: ! wall 0.167415 comb 0.170000 user 0.160000 sys 0.010000 (median of 58) revision: medium amount; added files: medium amount; rename small amount; d343da0c55a8 d7746d32bf9d before: ! wall 0.036820 comb 0.040000 user 0.040000 sys 0.000000 (median of 100) after: ! wall 0.035797 comb 0.040000 user 0.040000 sys 0.000000 (median of 100) The extra cost in the linear case can be reclaimed later with some extra logic. Differential Revision: https://phab.mercurial-scm.org/D7124
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Mercurial Rust Code

This directory contains various Rust code for the Mercurial project.

The top-level Cargo.toml file defines a workspace containing all primary Mercurial crates.

Building

To build the Rust components:

$ cargo build

If you prefer a non-debug / release configuration:

$ cargo build --release

Features

The following Cargo features are available:

localdev (default)

Produce files that work with an in-source-tree build.

In this mode, the build finds and uses a python2.7 binary from PATH. The hg binary assumes it runs from rust/target/<target>hg and it finds Mercurial files at dirname($0)/../../../.

Build Mechanism

The produced hg binary is bound to a CPython installation. The binary links against and loads a CPython library that is discovered at build time (by a build.rs Cargo build script). The Python standard library defined by this CPython installation is also used.

Finding the appropriate CPython installation to use is done by the python27-sys crate's build.rs. Its search order is:

  1. PYTHON_SYS_EXECUTABLE environment variable.
  2. python executable on PATH
  3. python2 executable on PATH
  4. python2.7 executable on PATH

Additional verification of the found Python will be performed by our build.rs to ensure it meets Mercurial's requirements.

Details about the build-time configured Python are built into the produced hg binary. This means that a built hg binary is only suitable for a specific, well-defined role. These roles are controlled by Cargo features (see above).

Running

The hgcli crate produces an hg binary. You can run this binary via cargo run:

$ cargo run --manifest-path hgcli/Cargo.toml

Or directly:

$ target/debug/hg
$ target/release/hg

You can also run the test harness with this binary:

$ ./run-tests.py --with-hg ../rust/target/debug/hg

Note

Integration with the test harness is still preliminary. Remember to cargo build after changes because the test harness doesn't yet automatically build Rust code.