From c6a5c8eb228bac2e7b3b45074daa0761de7208e0 Mon Sep 17 00:00:00 2001
From: Eidolon <furyhunter600@gmail.com>
Date: Sat, 20 Apr 2024 19:15:46 -0500
Subject: [PATCH] git: Always use OpenSSL on win32

By default, libssh2 uses Windows Cryptography Next Generation when targeting
win32. The wincng backend does not support ED25519, which is a widely-used
algorithm among git hosting services, and in some cases may be the only option
on remotes in certain configurations.

This change necessitates Windows users building jj to install openssl via vcpkg
for the target triple x64-windows-static-md when building for MSVC, or otherwise
have OpenSSL available at build time. This should also generally work when
building for MinGW, though I did not try it.

Fixes #3322
---
 .github/workflows/build.yml |  6 ++++++
 CHANGELOG.md                |  7 +++++++
 Cargo.lock                  |  1 +
 Cargo.toml                  |  1 +
 docs/windows.md             | 18 +++++++++++++++++-
 lib/Cargo.toml              |  1 +
 6 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 66db8228b9..9cfb45cc33 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -65,6 +65,12 @@ jobs:
         Remove-WindowsCapability -Online -Name OpenSSH.Client~~~~0.0.1.0
         choco install openssh --pre
 
+    # Windows builds need OpenSSL to fully support Git+SSH
+    - name: Setup openssl [windows]
+      if: ${{ matrix.os == 'windows-latest' }}
+      run: |
+        choco install openssl
+
     - name: Install Rust
       uses: dtolnay/rust-toolchain@1482605bfc5719782e1267fd0c0cc350fe7646b8
       with:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4ae03aa2f0..bd75b71858 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * The default template alias `builtin_log_root(change_id: ChangeId, commit_id: CommitId)` was replaced by `format_root_commit(root: Commit)`.
 
+* When targeting Windows, libssh2 will use OpenSSL rather than wincng. This fixes
+  interacting with Git+SSH hosts using ED25519 keys, but Windows developers will
+  need to provide OpenSSL at build time.
+
 ### New features
 
 * The list of conflicted paths is printed whenever the working copy changes.
@@ -64,6 +68,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   literals. This means that `snapshot.max-new-file-size="1"` and
   `snapshot.max-new-file-size=1` are now equivalent.
 
+* ED25519 host keys are now supported correctly when connecting to Git+SSH hosts
+  on Windows.
+
 ## [0.16.0] - 2024-04-03
 
 ### Deprecations
diff --git a/Cargo.lock b/Cargo.lock
index 9583441d98..39f019fcd4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1744,6 +1744,7 @@ dependencies = [
  "insta",
  "itertools 0.12.1",
  "jj-lib-proc-macros",
+ "libssh2-sys",
  "maplit",
  "num_cpus",
  "once_cell",
diff --git a/Cargo.toml b/Cargo.toml
index f4119936d9..83e8125825 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -60,6 +60,7 @@ indoc = "2.0.4"
 insta = { version = "1.38.0", features = ["filters"] }
 itertools = "0.12.1"
 libc = { version = "0.2.153" }
+libssh2-sys = { version = "0.3.0", features = ["openssl-on-win32"] }
 maplit = "1.0.2"
 minus = { version = "5.6.1", features = ["dynamic_output", "search"] }
 num_cpus = "1.16.0"
diff --git a/docs/windows.md b/docs/windows.md
index 5c55c434e7..25d3ac79d4 100644
--- a/docs/windows.md
+++ b/docs/windows.md
@@ -92,4 +92,20 @@ Mode. If those conditions are not satisfied, `jj` will materialize symlinks as
 ordinary files.
 
 For colocated repositories, Git support must also be enabled using the
-`git config` option `core.symlinks=true`.
\ No newline at end of file
+`git config` option `core.symlinks=true`.
+
+## Building jj on Windows
+
+By default, `jj` will build with `libssh2` using OpenSSL as its cryptography
+backend. This is because libssh2's wincng backend does not support the ED25519
+algorithm, preventing Git+SSH remotes using ED25519 keys from working.
+
+The easiest way to provide this is to install it via [vcpkg].
+
+```bash
+VCPKG_ROOT=path/to/your/vcpkg_installation
+vcpkg install --triplet=x64-windows-static-md openssl
+cargo build --release
+```
+
+[vcpkg]: https://vcpkg.io/
diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index d7a68f6a13..f84f366f24 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -49,6 +49,7 @@ hex = { workspace = true }
 ignore = { workspace = true }
 itertools = { workspace = true }
 jj-lib-proc-macros = { workspace = true }
+libssh2-sys = { workspace = true }
 maplit = { workspace = true }
 once_cell = { workspace = true }
 pest = { workspace = true }