From a721e6278182f79ba97eb114061be05cf766c9c3 Mon Sep 17 00:00:00 2001
From: Daniel Wagner-Hall <dawagner@gmail.com>
Date: Thu, 19 Mar 2020 23:29:31 +0000
Subject: [PATCH] Try installing exact versions before updating

When an exact version is being installed, if we already have that
version from the index, we don't need to update the index before
installing it. Don't do this if it's not an exact version, because the
update may find us a newer version.

This is particularly useful for scripts which unconditionally run
`cargo install some-crate --version=1.2.3`. Before install-update, I
wrote a crate to do this
(https://crates.io/crates/cargo-ensure-installed) which I'm trying to
replace with just `cargo install`, but the extra latency of updating the
index for a no-op is noticeable.

This introduces an interesting edge-case around yanked crates; the
yanked-ness of crates will no longer change on install for exact version
matches which were already downloaded. This feels niche enough to
hopefully not matter...
---
 src/cargo/ops/cargo_install.rs                | 10 +++++--
 src/cargo/ops/cargo_uninstall.rs              |  2 +-
 .../ops/common_for_install_and_uninstall.rs   | 28 ++++++++++++++++---
 tests/testsuite/install_upgrade.rs            |  3 +-
 4 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/src/cargo/ops/cargo_install.rs b/src/cargo/ops/cargo_install.rs
index 0ff2edbc6..b2759366e 100644
--- a/src/cargo/ops/cargo_install.rs
+++ b/src/cargo/ops/cargo_install.rs
@@ -151,7 +151,7 @@ fn install_one(
             krate,
             vers,
             config,
-            true,
+            NeedsUpdate::True,
             &mut |git| git.read_packages(),
         )?
     } else if source_id.is_path() {
@@ -180,7 +180,7 @@ fn install_one(
             }
         }
         src.update()?;
-        select_pkg(src, krate, vers, config, false, &mut |path| {
+        select_pkg(src, krate, vers, config, NeedsUpdate::False, &mut |path| {
             path.read_packages()
         })?
     } else {
@@ -189,7 +189,11 @@ fn install_one(
             krate,
             vers,
             config,
-            is_first_install,
+            if is_first_install {
+                NeedsUpdate::TryWithoutFirst
+            } else {
+                NeedsUpdate::False
+            },
             &mut |_| {
                 bail!(
                     "must specify a crate to install from \
diff --git a/src/cargo/ops/cargo_uninstall.rs b/src/cargo/ops/cargo_uninstall.rs
index 2d69eabd0..612db0129 100644
--- a/src/cargo/ops/cargo_uninstall.rs
+++ b/src/cargo/ops/cargo_uninstall.rs
@@ -85,7 +85,7 @@ fn uninstall_cwd(root: &Filesystem, bins: &[String], config: &Config) -> CargoRe
     let tracker = InstallTracker::load(config, root)?;
     let source_id = SourceId::for_path(config.cwd())?;
     let src = path_source(source_id, config)?;
-    let pkg = select_pkg(src, None, None, config, true, &mut |path| {
+    let pkg = select_pkg(src, None, None, config, NeedsUpdate::True, &mut |path| {
         path.read_packages()
     })?;
     let pkgid = pkg.package_id();
diff --git a/src/cargo/ops/common_for_install_and_uninstall.rs b/src/cargo/ops/common_for_install_and_uninstall.rs
index aa5c4ee18..b61ebc5c8 100644
--- a/src/cargo/ops/common_for_install_and_uninstall.rs
+++ b/src/cargo/ops/common_for_install_and_uninstall.rs
@@ -525,13 +525,20 @@ pub fn path_source(source_id: SourceId, config: &Config) -> CargoResult<PathSour
     Ok(PathSource::new(&path, source_id, config))
 }
 
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum NeedsUpdate {
+    True,
+    False,
+    TryWithoutFirst,
+}
+
 /// Gets a Package based on command-line requirements.
 pub fn select_pkg<'a, T>(
     mut source: T,
     name: Option<&str>,
     vers: Option<&str>,
     config: &Config,
-    needs_update: bool,
+    needs_update: NeedsUpdate,
     list_all: &mut dyn FnMut(&mut T) -> CargoResult<Vec<Package>>,
 ) -> CargoResult<Package>
 where
@@ -542,7 +549,7 @@ where
     // with other global Cargos
     let _lock = config.acquire_package_cache_lock()?;
 
-    if needs_update {
+    if let NeedsUpdate::True = needs_update {
         source.update()?;
     }
 
@@ -603,8 +610,21 @@ where
             vers
         };
         let dep = Dependency::parse_no_deprecated(name, vers_spec, source.source_id())?;
-        let deps = source.query_vec(&dep)?;
-        match deps.iter().map(|p| p.package_id()).max() {
+        let deps = (|| {
+            if let Some(vers_spec) = vers_spec {
+                if semver::VersionReq::parse(vers_spec).unwrap().is_exact() {
+                    let deps = source.query_vec(&dep)?;
+                    if deps.len() == 1 {
+                        return Ok(deps);
+                    }
+                }
+            }
+            if needs_update != NeedsUpdate::False {
+                source.update()?;
+            }
+            source.query_vec(&dep)
+        })();
+        match deps?.iter().map(|p| p.package_id()).max() {
             Some(pkgid) => {
                 let pkg = Box::new(&mut source).download_now(pkgid, config)?;
                 Ok(pkg)
diff --git a/tests/testsuite/install_upgrade.rs b/tests/testsuite/install_upgrade.rs
index ee69bd85b..3d51ad625 100644
--- a/tests/testsuite/install_upgrade.rs
+++ b/tests/testsuite/install_upgrade.rs
@@ -225,8 +225,7 @@ fn ambiguous_version_no_longer_allowed() {
     cargo_process("install foo --version=1.0")
         .with_stderr(
             "\
-[UPDATING] `[..]` index
-[ERROR] the `--vers` provided, `1.0`, is not a valid semver version: cannot parse '1.0' as a semver
+error: the `--vers` provided, `1.0`, is not a valid semver version: cannot parse '1.0' as a semver
 
 if you want to specify semver range, add an explicit qualifier, like ^1.0
 ",