From 15c7c0847aac42c4f60569ef3e94581fcf9c18c1 Mon Sep 17 00:00:00 2001
From: Jacob Finkelman <jfinkelm@amazon.com>
Date: Wed, 2 Mar 2022 23:03:14 +0000
Subject: [PATCH 1/2] Use locked_version more

---
 src/cargo/core/resolver/errors.rs | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/cargo/core/resolver/errors.rs b/src/cargo/core/resolver/errors.rs
index 5cabd01bae4..8d497527276 100644
--- a/src/cargo/core/resolver/errors.rs
+++ b/src/cargo/core/resolver/errors.rs
@@ -95,7 +95,15 @@ pub(super) fn activation_error(
 
         msg.push_str("\nversions that meet the requirements `");
         msg.push_str(&dep.version_req().to_string());
-        msg.push_str("` are: ");
+        msg.push_str("` ");
+
+        if let Some(v) = dep.version_req().locked_version() {
+            msg.push_str("(locked to ");
+            msg.push_str(&v.to_string());
+            msg.push_str(") ");
+        }
+
+        msg.push_str("are: ");
         msg.push_str(
             &candidates
                 .iter()
@@ -239,12 +247,19 @@ pub(super) fn activation_error(
                 versions.join(", ")
             };
 
+            let locked_version = dep
+                .version_req()
+                .locked_version()
+                .map(|v| format!(" (locked to {})", v))
+                .unwrap_or_default();
+
             let mut msg = format!(
-                "failed to select a version for the requirement `{} = \"{}\"`\n\
+                "failed to select a version for the requirement `{} = \"{}\"`{}\n\
                  candidate versions found which didn't match: {}\n\
                  location searched: {}\n",
                 dep.package_name(),
                 dep.version_req(),
+                locked_version,
                 versions,
                 registry.describe_source(dep.source_id()),
             );
@@ -254,7 +269,7 @@ pub(super) fn activation_error(
             // If we have a path dependency with a locked version, then this may
             // indicate that we updated a sub-package and forgot to run `cargo
             // update`. In this case try to print a helpful error!
-            if dep.source_id().is_path() && dep.version_req().to_string().starts_with('=') {
+            if dep.source_id().is_path() && dep.version_req().is_locked() {
                 msg.push_str(
                     "\nconsider running `cargo update` to update \
                      a path dependency's locked version",

From 4164c46a1b6d7ebf017ab0db1a7659be2a5a21e8 Mon Sep 17 00:00:00 2001
From: Jacob Finkelman <jfinkelm@amazon.com>
Date: Thu, 3 Mar 2022 18:30:44 +0000
Subject: [PATCH 2/2] add a test

---
 tests/testsuite/lockfile_compat.rs | 52 ++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/tests/testsuite/lockfile_compat.rs b/tests/testsuite/lockfile_compat.rs
index 0be1d4aa693..9f490cae2fb 100644
--- a/tests/testsuite/lockfile_compat.rs
+++ b/tests/testsuite/lockfile_compat.rs
@@ -836,3 +836,55 @@ source = "git+{url}#{sha}"
 
     assert_eq!(p.read_file("Cargo.lock"), lockfile);
 }
+
+#[cargo_test]
+fn bad_data_in_lockfile_error_meg() {
+    Package::new("bar", "0.0.1").publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "test"
+                version = "0.0.0"
+
+                [dependencies]
+                bar = "*"
+            "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .file(
+            "Cargo.lock",
+            r#"# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "bar"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e1b9346248cf3391ead604c4407258d327c28e37209f6d56127598165165dda"
+
+[[package]]
+name = "test"
+version = "0.0.0"
+dependencies = [
+ "bar",
+]"#,
+        )
+        .build();
+    p.cargo("build")
+        .with_status(101)
+        .with_stderr(
+            "\
+[..]
+[ERROR] failed to select a version for the requirement `bar = \"*\"` (locked to 0.1.0)
+candidate versions found which didn't match: 0.0.1
+location searched: `dummy-registry` index (which is replacing registry `crates-io`)
+required by package `test v0.0.0 ([..])`
+perhaps a crate was updated and forgotten to be re-vendored?
+",
+        )
+        .run();
+}