cargo install: Ignore Cargo.lock for non --path installs.

Requires `--locked` to use Cargo.lock for registry and git installs.

src/cargo/core/workspace.rs

@@ -77,6 +77,10 @@ pub struct Workspace<'cfg> {
     // A cache of loaded packages for particular paths which is disjoint from
     // `packages` up above, used in the `load` method down below.
     loaded_packages: RefCell<HashMap<PathBuf, Package>>,
+
+    // If `true`, then the resolver will ignore any existing `Cargo.lock`
+    // file. This is set for `cargo install` without `--locked`.
+    ignore_lock: bool,
 }
 
 // Separate structure for tracking loaded packages (to avoid loading anything
@@ -148,6 +152,7 @@ impl<'cfg> Workspace<'cfg> {
             is_ephemeral: false,
             require_optional_deps: true,
             loaded_packages: RefCell::new(HashMap::new()),
+            ignore_lock: false,
         };
         ws.root_manifest = ws.find_root(manifest_path)?;
         ws.find_members()?;
@@ -184,6 +189,7 @@ impl<'cfg> Workspace<'cfg> {
             is_ephemeral: true,
             require_optional_deps,
             loaded_packages: RefCell::new(HashMap::new()),
+            ignore_lock: false,
         };
         {
             let key = ws.current_manifest.parent().unwrap();
@@ -320,14 +326,23 @@ impl<'cfg> Workspace<'cfg> {
         self.require_optional_deps
     }
 
-    pub fn set_require_optional_deps<'a>(
-        &'a mut self,
+    pub fn set_require_optional_deps(
+        &mut self,
         require_optional_deps: bool,
     ) -> &mut Workspace<'cfg> {
         self.require_optional_deps = require_optional_deps;
         self
     }
 
+    pub fn ignore_lock(&self) -> bool {
+        self.ignore_lock
+    }
+
+    pub fn set_ignore_lock(&mut self, ignore_lock: bool) -> &mut Workspace<'cfg> {
+        self.ignore_lock = ignore_lock;
+        self
+    }
+
     /// Finds the root of a workspace for the crate whose manifest is located
     /// at `manifest_path`.
     ///

src/cargo/ops/cargo_install.rs

@@ -215,7 +215,11 @@ fn install_one(
     };
 
     let ws = match overidden_target_dir {
-        Some(dir) => Workspace::ephemeral(pkg, config, Some(dir), false)?,
+        Some(dir) => {
+            let mut ws = Workspace::ephemeral(pkg, config, Some(dir), false)?;
+            ws.set_ignore_lock(config.lock_update_allowed());
+            ws
+        }
         None => {
             let mut ws = Workspace::new(pkg.manifest_path(), config)?;
             ws.set_require_optional_deps(false);

src/cargo/ops/resolve.rs

@@ -64,7 +64,9 @@ pub fn resolve_ws_with_method<'a>(
     }
     let mut add_patches = true;
 
-    let resolve = if ws.require_optional_deps() {
+    let resolve = if ws.ignore_lock() {
+        None
+    } else if ws.require_optional_deps() {
         // First, resolve the root_package's *listed* dependencies, as well as
         // downloading and updating all remotes and such.
         let resolve = resolve_with_registry(ws, &mut registry, false)?;

tests/testsuite/install.rs

@@ -1190,6 +1190,8 @@ fn custom_target_dir_for_git_source() {
 
 #[test]
 fn install_respects_lock_file() {
+    // `cargo install` now requires --locked to use a Cargo.lock for non
+    // --path installs.
     Package::new("bar", "0.1.0").publish();
     Package::new("bar", "0.1.1")
         .file("src/lib.rs", "not rust")
@@ -1219,7 +1221,52 @@ dependencies = [
         )
         .publish();
 
-    cargo_process("install foo").run();
+    cargo_process("install foo")
+        .with_stderr_contains("[..]not rust[..]")
+        .with_status(101)
+        .run();
+    cargo_process("install --locked foo").run();
+}
+
+#[test]
+fn install_path_respects_lock_file() {
+    // For --path installs, always use local Cargo.lock.
+    Package::new("bar", "0.1.0").publish();
+    Package::new("bar", "0.1.1")
+        .file("src/lib.rs", "not rust")
+        .publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            bar = "0.1"
+            "#,
+        )
+        .file("src/main.rs", "extern crate bar; fn main() {}")
+        .file(
+            "Cargo.lock",
+            r#"
+[[package]]
+name = "bar"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "foo"
+version = "0.1.0"
+dependencies = [
+ "bar 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+"#,
+        )
+        .build();
+
+    p.cargo("install --path .").run();
 }
 
 #[test]