fix(msrv): Report all incompatible packages, not just a random one

src/cargo/ops/cargo_compile/mod.rs

@@ -487,6 +487,8 @@ pub fn create_bcx<'a, 'gctx>(
             current_version.patch,
         );
 
+        let mut incompatible = Vec::new();
+        let mut local_incompatible = false;
         for unit in unit_graph.keys() {
             let Some(version) = unit.pkg.rust_version() else {
                 continue;
@@ -497,35 +499,40 @@ pub fn create_bcx<'a, 'gctx>(
                 continue;
             }
 
-            let guidance = if ws.is_ephemeral() {
+            local_incompatible |= unit.is_local();
+            incompatible.push((unit, version));
+        }
+        if !incompatible.is_empty() {
+            use std::fmt::Write as _;
+
+            let plural = if incompatible.len() == 1 { "" } else { "s" };
+            let mut message = format!(
+                "rustc {current_version} is not supported by the following package{plural}:\n"
+            );
+            incompatible.sort_by_key(|(unit, _)| (unit.pkg.name(), unit.pkg.version()));
+            for (unit, msrv) in incompatible {
+                let name = &unit.pkg.name();
+                let version = &unit.pkg.version();
+                writeln!(&mut message, "  {name}@{version} requires rustc {msrv}").unwrap();
+            }
+            if ws.is_ephemeral() {
                 if ws.ignore_lock() {
-                    "Try re-running cargo install with `--locked`".to_string()
-                } else {
-                    String::new()
+                    writeln!(
+                        &mut message,
+                        "Try re-running `cargo install` with `--locked`"
+                    )
+                    .unwrap();
                 }
-            } else if !unit.is_local() {
-                format!(
-                    "Either upgrade to rustc {} or newer, or use\n\
-                     cargo update {}@{} --precise ver\n\
-                     where `ver` is the latest version of `{}` supporting rustc {}",
-                    version,
-                    unit.pkg.name(),
-                    unit.pkg.version(),
-                    unit.pkg.name(),
-                    current_version,
+            } else if !local_incompatible {
+                writeln!(
+                    &mut message,
+                    "Either upgrade rustc or select compatible dependency versions with
+`cargo update <name>@<current-ver> --precise <compatible-ver>`
+where `<compatible-ver>` is the latest version supporting rustc {current_version}",
                 )
-            } else {
-                String::new()
-            };
-
-            anyhow::bail!(
-                "package `{}` cannot be built because it requires rustc {} or newer, \
-                 while the currently active rustc version is {}\n{}",
-                unit.pkg,
-                version,
-                current_version,
-                guidance,
-            );
+                .unwrap();
+            }
+            return Err(anyhow::Error::msg(message));
         }
     }
 

tests/testsuite/rust_version.rs

@@ -179,8 +179,11 @@ fn rust_version_too_high() {
     p.cargo("check")
         .with_status(101)
         .with_stderr(
-            "error: package `foo v0.0.1 ([..])` cannot be built because it requires \
-             rustc 1.9876.0 or newer, while the currently active rustc version is [..]\n\n",
+            "\
+[ERROR] rustc [..] is not supported by the following package:
+  [email protected] requires rustc 1.9876.0
+
+",
         )
         .run();
     p.cargo("check --ignore-rust-version").run();
@@ -212,14 +215,66 @@ fn dependency_rust_version_newer_than_rustc() {
     p.cargo("check")
         .with_status(101)
         .with_stderr(
-            "    Updating `[..]` index\n \
-             Downloading crates ...\n  \
-             Downloaded bar v0.0.1 (registry `[..]`)\n\
-             error: package `bar v0.0.1` cannot be built because it requires \
-             rustc 1.2345.0 or newer, while the currently active rustc version is [..]\n\
-             Either upgrade to rustc 1.2345.0 or newer, or use\n\
-             cargo update [email protected] --precise ver\n\
-             where `ver` is the latest version of `bar` supporting rustc [..]",
+            "\
+[UPDATING] `[..]` index
+[DOWNLOADING] crates ...
+[DOWNLOADED] bar v0.0.1 (registry `[..]`)
+[ERROR] rustc [..] is not supported by the following package:
+  [email protected] requires rustc 1.2345.0
+Either upgrade rustc or select compatible dependency versions with
+`cargo update <name>@<current-ver> --precise <compatible-ver>`
+where `<compatible-ver>` is the latest version supporting rustc [..]
+
+",
+        )
+        .run();
+    p.cargo("check --ignore-rust-version").run();
+}
+
+#[cargo_test]
+fn dependency_tree_rust_version_newer_than_rustc() {
+    Package::new("baz", "0.0.1")
+        .dep("bar", "0.0.1")
+        .rust_version("1.2345.0")
+        .file("src/lib.rs", "fn other_stuff() {}")
+        .publish();
+    Package::new("bar", "0.0.1")
+        .rust_version("1.2345.0")
+        .file("src/lib.rs", "fn other_stuff() {}")
+        .publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            edition = "2015"
+            authors = []
+            [dependencies]
+            baz = "0.0.1"
+        "#,
+        )
+        .file("src/main.rs", "fn main(){}")
+        .build();
+
+    p.cargo("check")
+        .with_status(101)
+        .with_stderr(
+            "\
+[UPDATING] `[..]` index
+[DOWNLOADING] crates ...
+[DOWNLOADED] baz v0.0.1 (registry `[..]`)
+[DOWNLOADED] bar v0.0.1 (registry `[..]`)
+[ERROR] rustc [..] is not supported by the following packages:
+  [email protected] requires rustc 1.2345.0
+  [email protected] requires rustc 1.2345.0
+Either upgrade rustc or select compatible dependency versions with
+`cargo update <name>@<current-ver> --precise <compatible-ver>`
+where `<compatible-ver>` is the latest version supporting rustc [..]
+
+",
         )
         .run();
     p.cargo("check --ignore-rust-version").run();