Auto merge of #8243 - ehuss:patch-unused-can-update, r=alexcrichton

Fix `cargo update` with unused patch.

If you end up with an unused patch in `Cargo.lock`, then you try to update the patch to a version that does not match the original unused patch, and run `cargo update`, Cargo refuses to update it with the error "patch for `bar` in `/~https://github.com/rust-lang/crates.io-index` did not resolve to any crates".  At this point, Cargo seems to be permanently stuck with no way to update it (unless you manually edit `Cargo.lock`).

The solution here is to add the unused patches to the "to_avoid" list, so that `cargo update` is allowed to update them.

I am uncertain if this is the best way to fix it, but seems to match my intuition of how `cargo update` is implemented.

src/cargo/ops/cargo_generate_lockfile.rs

@@ -5,7 +5,7 @@ use termcolor::Color::{self, Cyan, Green, Red};
 
 use crate::core::registry::PackageRegistry;
 use crate::core::resolver::ResolveOpts;
-use crate::core::PackageId;
+use crate::core::{PackageId, PackageIdSpec};
 use crate::core::{Resolve, SourceId, Workspace};
 use crate::ops;
 use crate::util::config::Config;
@@ -79,6 +79,7 @@ pub fn update_lockfile(ws: &Workspace<'_>, opts: &UpdateOptions<'_>) -> CargoRes
 
     if opts.to_update.is_empty() {
         to_avoid.extend(previous_resolve.iter());
+        to_avoid.extend(previous_resolve.unused_patches());
     } else {
         let mut sources = Vec::new();
         for name in opts.to_update.iter() {
@@ -102,6 +103,11 @@ pub fn update_lockfile(ws: &Workspace<'_>, opts: &UpdateOptions<'_>) -> CargoRes
                     None => dep.source_id().with_precise(None),
                 });
             }
+            if let Ok(unused_id) =
+                PackageIdSpec::query_str(name, previous_resolve.unused_patches().iter().cloned())
+            {
+                to_avoid.insert(unused_id);
+            }
         }
 
         registry.add_sources(sources)?;

tests/testsuite/patch.rs

@@ -1445,3 +1445,79 @@ fn canonicalize_a_bunch() {
     p.cargo("build").with_stderr("[FINISHED] [..]").run();
     p.cargo("build").with_stderr("[FINISHED] [..]").run();
 }
+
+#[cargo_test]
+fn update_unused_new_version() {
+    // If there is an unused patch entry, and then you update the patch,
+    // make sure `cargo update` will be able to fix the lock file.
+    Package::new("bar", "0.1.5").publish();
+
+    // Start with a lock file to 0.1.5, and an "unused" patch because the
+    // version is too old.
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+
+                [dependencies]
+                bar = "0.1.5"
+
+                [patch.crates-io]
+                bar = { path = "../bar" }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    // Patch is too old.
+    let bar = project()
+        .at("bar")
+        .file("Cargo.toml", &basic_manifest("bar", "0.1.4"))
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build")
+        .with_stderr_contains("[WARNING] Patch `bar v0.1.4 [..] was not used in the crate graph.")
+        .run();
+    // unused patch should be in the lock file
+    let lock = p.read_lockfile();
+    let toml: toml::Value = toml::from_str(&lock).unwrap();
+    assert_eq!(toml["patch"]["unused"].as_array().unwrap().len(), 1);
+    assert_eq!(toml["patch"]["unused"][0]["name"].as_str(), Some("bar"));
+    assert_eq!(
+        toml["patch"]["unused"][0]["version"].as_str(),
+        Some("0.1.4")
+    );
+
+    // Oh, OK, let's update to the latest version.
+    bar.change_file("Cargo.toml", &basic_manifest("bar", "0.1.6"));
+
+    // Create a backup so we can test it with different options.
+    fs::copy(p.root().join("Cargo.lock"), p.root().join("Cargo.lock.bak")).unwrap();
+
+    // Try with `-p`.
+    p.cargo("update -p bar")
+        .with_stderr(
+            "\
+[UPDATING] `[..]/registry` index
+[ADDING] bar v0.1.6 ([..]/bar)
+[REMOVING] bar v0.1.5
+",
+        )
+        .run();
+
+    // Try with bare `cargo update`.
+    fs::copy(p.root().join("Cargo.lock.bak"), p.root().join("Cargo.lock")).unwrap();
+    p.cargo("update")
+        .with_stderr(
+            "\
+[UPDATING] `[..]/registry` index
+[ADDING] bar v0.1.6 ([..]/bar)
+[REMOVING] bar v0.1.5
+",
+        )
+        .run();
+}