Auto merge of #7191 - debris:prerelease_error_message, r=Eh2406

improve error message for unmatched prerelease dependencies

fixes #7007

error message before:

```
error: no matching package named `a` found
location searched: [..]
perhaps you meant: a
required by package `b v0.1.0 ([..])`
```

error message now

```
error: no matching package named `a` found
location searched: [..]
prerelease package needs to be specified explicitly
a = { version = "0.1.1-alpha.0" }
required by package `b v0.1.0 ([..])`
```

Author: bors

src/cargo/core/resolver/errors.rs

@@ -203,100 +203,115 @@ pub(super) fn activation_error(
     };
     candidates.sort_unstable_by(|a, b| b.version().cmp(a.version()));
 
-    let mut msg = if !candidates.is_empty() {
-        let versions = {
-            let mut versions = candidates
-                .iter()
-                .take(3)
-                .map(|cand| cand.version().to_string())
-                .collect::<Vec<_>>();
+    let mut msg =
+        if !candidates.is_empty() {
+            let versions = {
+                let mut versions = candidates
+                    .iter()
+                    .take(3)
+                    .map(|cand| cand.version().to_string())
+                    .collect::<Vec<_>>();
+
+                if candidates.len() > 3 {
+                    versions.push("...".into());
+                }
+
+                versions.join(", ")
+            };
+
+            let mut msg = format!(
+                "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(),
+                versions,
+                registry.describe_source(dep.source_id()),
+            );
+            msg.push_str("required by ");
+            msg.push_str(&describe_path(
+                &cx.parents.path_to_bottom(&parent.package_id()),
+            ));
 
-            if candidates.len() > 3 {
-                versions.push("...".into());
+            // 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('=') {
+                msg.push_str(
+                    "\nconsider running `cargo update` to update \
+                     a path dependency's locked version",
+                );
             }
 
-            versions.join(", ")
-        };
-
-        let mut msg = format!(
-            "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(),
-            versions,
-            registry.describe_source(dep.source_id()),
-        );
-        msg.push_str("required by ");
-        msg.push_str(&describe_path(
-            &cx.parents.path_to_bottom(&parent.package_id()),
-        ));
-
-        // 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('=') {
-            msg.push_str(
-                "\nconsider running `cargo update` to update \
-                 a path dependency's locked version",
-            );
-        }
-
-        if registry.is_replaced(dep.source_id()) {
-            msg.push_str("\nperhaps a crate was updated and forgotten to be re-vendored?");
-        }
+            if registry.is_replaced(dep.source_id()) {
+                msg.push_str("\nperhaps a crate was updated and forgotten to be re-vendored?");
+            }
 
-        msg
-    } else {
-        // Maybe the user mistyped the name? Like `dep-thing` when `Dep_Thing`
-        // was meant. So we try asking the registry for a `fuzzy` search for suggestions.
-        let mut candidates = Vec::new();
-        if let Err(e) = registry.query(&new_dep, &mut |s| candidates.push(s.name()), true) {
-            return to_resolve_err(e);
-        };
-        candidates.sort_unstable();
-        candidates.dedup();
-        let mut candidates: Vec<_> = candidates
-            .iter()
-            .map(|n| (lev_distance(&*new_dep.package_name(), &*n), n))
-            .filter(|&(d, _)| d < 4)
-            .collect();
-        candidates.sort_by_key(|o| o.0);
-        let mut msg = format!(
-            "no matching package named `{}` found\n\
-             location searched: {}\n",
-            dep.package_name(),
-            dep.source_id()
-        );
-        if !candidates.is_empty() {
-            let mut names = candidates
+            msg
+        } else {
+            // Maybe the user mistyped the name? Like `dep-thing` when `Dep_Thing`
+            // was meant. So we try asking the registry for a `fuzzy` search for suggestions.
+            let mut candidates = Vec::new();
+            if let Err(e) = registry.query(&new_dep, &mut |s| candidates.push(s.clone()), true) {
+                return to_resolve_err(e);
+            };
+            candidates.sort_unstable_by(|a, b| a.name().cmp(&b.name()));
+            candidates.dedup_by(|a, b| a.name() == b.name());
+            let mut candidates: Vec<_> = candidates
                 .iter()
-                .take(3)
-                .map(|c| c.1.as_str())
-                .collect::<Vec<_>>();
-
-            if candidates.len() > 3 {
-                names.push("...");
+                .map(|n| (lev_distance(&*new_dep.package_name(), &*n.name()), n))
+                .filter(|&(d, _)| d < 4)
+                .collect();
+            candidates.sort_by_key(|o| o.0);
+            let mut msg = format!(
+                "no matching package named `{}` found\n\
+                 location searched: {}\n",
+                dep.package_name(),
+                dep.source_id()
+            );
+            if !candidates.is_empty() {
+                // If dependency package name is equal to the name of the candidate here
+                // it may be a prerelease package which hasn't been speficied correctly
+                if dep.package_name() == candidates[0].1.name()
+                    && candidates[0].1.package_id().version().is_prerelease()
+                {
+                    msg.push_str("prerelease package needs to be specified explicitly\n");
+                    msg.push_str(&format!(
+                        "{name} = {{ version = \"{version}\" }}",
+                        name = candidates[0].1.name(),
+                        version = candidates[0].1.package_id().version()
+                    ));
+                } else {
+                    let mut names = candidates
+                        .iter()
+                        .take(3)
+                        .map(|c| c.1.name().as_str())
+                        .collect::<Vec<_>>();
+
+                    if candidates.len() > 3 {
+                        names.push("...");
+                    }
+
+                    msg.push_str("perhaps you meant: ");
+                    msg.push_str(&names.iter().enumerate().fold(
+                        String::default(),
+                        |acc, (i, el)| match i {
+                            0 => acc + el,
+                            i if names.len() - 1 == i && candidates.len() <= 3 => acc + " or " + el,
+                            _ => acc + ", " + el,
+                        },
+                    ));
+                }
+
+                msg.push_str("\n");
             }
-
-            msg.push_str("perhaps you meant: ");
-            msg.push_str(&names.iter().enumerate().fold(
-                String::default(),
-                |acc, (i, el)| match i {
-                    0 => acc + el,
-                    i if names.len() - 1 == i && candidates.len() <= 3 => acc + " or " + el,
-                    _ => acc + ", " + el,
-                },
+            msg.push_str("required by ");
+            msg.push_str(&describe_path(
+                &cx.parents.path_to_bottom(&parent.package_id()),
             ));
-            msg.push_str("\n");
-        }
-        msg.push_str("required by ");
-        msg.push_str(&describe_path(
-            &cx.parents.path_to_bottom(&parent.package_id()),
-        ));
 
-        msg
-    };
+            msg
+        };
 
     if let Some(config) = config {
         if config.offline() {

tests/testsuite/registry.rs

@@ -1395,6 +1395,55 @@ fn use_semver() {
     p.cargo("build").run();
 }
 
+#[cargo_test]
+fn use_semver_package_incorrectly() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [workspace]
+            members = ["a", "b"]
+            "#,
+        )
+        .file(
+            "a/Cargo.toml",
+            r#"
+            [project]
+            name = "a"
+            version = "0.1.1-alpha.0"
+            authors = []
+            "#,
+        )
+        .file(
+            "b/Cargo.toml",
+            r#"
+            [project]
+            name = "b"
+            version = "0.1.0"
+            authors = []
+
+            [dependencies]
+            a = { version = "^0.1", path = "../a" }
+            "#,
+        )
+        .file("a/src/main.rs", "fn main() {}")
+        .file("b/src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("build")
+        .with_status(101)
+        .with_stderr(
+            "\
+error: no matching package named `a` found
+location searched: [..]
+prerelease package needs to be specified explicitly
+a = { version = \"0.1.1-alpha.0\" }
+required by package `b v0.1.0 ([..])`
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn only_download_relevant() {
     let p = project()