patch can conflict on not activated packages

Author: Eh2406

src/cargo/core/resolver/mod.rs

@@ -823,15 +823,12 @@ fn generalize_conflicting(
     dep: &Dependency,
     conflicting_activations: &ConflictMap,
 ) -> Option<ConflictMap> {
-    if conflicting_activations.is_empty() {
-        return None;
-    }
     // We need to determine the `ContextAge` that this `conflicting_activations` will jump to, and why.
-    let (backtrack_critical_age, backtrack_critical_id) = conflicting_activations
-        .keys()
-        .map(|&c| (cx.is_active(c).expect("not currently active!?"), c))
-        .max()
-        .unwrap();
+    let (backtrack_critical_age, backtrack_critical_id) = shortcircuit_max(
+        conflicting_activations
+            .keys()
+            .map(|&c| cx.is_active(c).map(|a| (a, c))),
+    )?;
     let backtrack_critical_reason: ConflictReason =
         conflicting_activations[&backtrack_critical_id].clone();
 
@@ -923,6 +920,19 @@ fn generalize_conflicting(
     None
 }
 
+/// Returns Some of the largest item in the iterator.
+/// Returns None if any of the items are None or the iterator is empty.
+fn shortcircuit_max<I: Ord>(iter: impl Iterator<Item = Option<I>>) -> Option<I> {
+    let mut out = None;
+    for i in iter {
+        if i.is_none() {
+            return None;
+        }
+        out = std::cmp::max(out, i);
+    }
+    out
+}
+
 /// Looks through the states in `backtrack_stack` for dependencies with
 /// remaining candidates. For each one, also checks if rolling back
 /// could change the outcome of the failed resolution that caused backtracking
@@ -949,12 +959,10 @@ fn find_candidate(
     // the cause of that backtrack, so we do not update it.
     let age = if !backtracked {
         // we don't have abnormal situations. So we can ask `cx` for how far back we need to go.
-        let a = cx.is_conflicting(Some(parent.package_id()), conflicting_activations);
-        // If the `conflicting_activations` does not apply to `cx`, then something went very wrong
-        // in building it. But we will just fall back to laboriously trying all possibilities witch
-        // will give us the correct answer so only `assert` if there is a developer to debug it.
-        debug_assert!(a.is_some());
-        a
+        // If the `conflicting_activations` does not apply to `cx`,
+        // we will just fall back to laboriously trying all possibilities witch
+        // will give us the correct answer.
+        cx.is_conflicting(Some(parent.package_id()), conflicting_activations)
     } else {
         None
     };

tests/testsuite/patch.rs

@@ -2541,3 +2541,105 @@ foo v0.1.0 [..]
         ))
         .run();
 }
+
+// From https://github.com/rust-lang/cargo/issues/7463
+#[cargo_test]
+fn patch_eq_conflict_panic() {
+    Package::new("bar", "0.1.0").publish();
+    Package::new("bar", "0.1.1").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+
+                [dependencies]
+                bar = "=0.1.0"
+
+                [dev-dependencies]
+                bar = "=0.1.1"
+
+                [patch.crates-io]
+                bar = {path="bar"}
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.1.1"))
+        .file("bar/src/lib.rs", "")
+        .build();
+
+    p.cargo("generate-lockfile")
+        .with_status(101)
+        .with_stderr(
+            r#"[UPDATING] `dummy-registry` index
+[ERROR] failed to select a version for `bar`.
+    ... required by package `foo v0.1.0 ([..])`
+versions that meet the requirements `=0.1.1` are: 0.1.1
+
+all possible versions conflict with previously selected packages.
+
+  previously selected package `bar v0.1.0`
+    ... which satisfies dependency `bar = "=0.1.0"` of package `foo v0.1.0 ([..])`
+
+failed to select a version for `bar` which could resolve this conflict
+"#,
+        )
+        .run();
+}
+
+// From https://github.com/rust-lang/cargo/issues/11336
+#[cargo_test]
+fn mismatched_version2() {
+    Package::new("qux", "0.1.0-beta.1").publish();
+    Package::new("qux", "0.1.0-beta.2").publish();
+    Package::new("bar", "0.1.0")
+        .dep("qux", "=0.1.0-beta.1")
+        .publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                 [package]
+                 name = "foo"
+                 version = "0.1.0"
+
+                 [dependencies]
+                 bar = "0.1.0"
+                 qux = "0.1.0-beta.2"
+
+                 [patch.crates-io]
+                 qux = { path = "qux" }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "qux/Cargo.toml",
+            r#"
+                [package]
+                name = "qux"
+                version = "0.1.0-beta.1"
+            "#,
+        )
+        .file("qux/src/lib.rs", "")
+        .build();
+
+    p.cargo("generate-lockfile")
+        .with_status(101)
+        .with_stderr(
+            r#"[UPDATING] `dummy-registry` index
+[ERROR] failed to select a version for `qux`.
+    ... required by package `bar v0.1.0`
+    ... which satisfies dependency `bar = "^0.1.0"` of package `foo v0.1.0 ([..])`
+versions that meet the requirements `=0.1.0-beta.1` are: 0.1.0-beta.1
+
+all possible versions conflict with previously selected packages.
+
+  previously selected package `qux v0.1.0-beta.2`
+    ... which satisfies dependency `qux = "^0.1.0-beta.2"` of package `foo v0.1.0 ([..])`
+
+failed to select a version for `qux` which could resolve this conflict"#,
+        )
+        .run();
+}