Add more context to publish-failed error message (#15879)

## What does this PR try to resolve?

This PR fixes issue #15754 where workspace publish failures provided
non-actionable error messages. Previously, when publishing a workspace
failed (due to rate limiting or other errors), users only saw generic
errors like `[ERROR] failed to publish to registry` without knowing
which package failed or what packages remained to be published.

## How to test and review this PR?

**Testing**: Run `cargo test workspace_publish_rate_limit_error` to see
the improved behavior, then `cargo test publish` to ensure all tests
pass.

**Review**:
- **Commit 1**: Adds test demonstrating current problematic behavior
- **Commit 2**: Implements fix and updates test to expect improved
output

The fix transforms error messages from generic `failed to publish to
registry` to actionable `failed to publish 'package_a' v0.1.0; the
following crates have not been published yet: package_b v0.1.0,
package_c v0.1.0`. This improvement applies consistently across all
publish error scenarios, giving users clear information about what went
wrong and what remains to be done.

src/cargo/ops/registry/publish.rs

@@ -210,7 +210,8 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
         // `b`, and we uploaded `a` and `b` but only confirmed `a`, then on
         // the following pass through the outer loop nothing will be ready for
         // upload.
-        for pkg_id in plan.take_ready() {
+        let mut ready = plan.take_ready();
+        while let Some(pkg_id) = ready.pop_first() {
             let (pkg, (_features, tarball)) = &pkg_dep_graph.packages[&pkg_id];
             opts.gctx.shell().status("Uploading", pkg.package_id())?;
 
@@ -236,6 +237,19 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
                 )?));
             }
 
+            let workspace_context = || {
+                let mut remaining = ready.clone();
+                remaining.extend(plan.iter());
+                if !remaining.is_empty() {
+                    format!(
+                        "\n\nnote: the following crates have not been published yet:\n  {}",
+                        remaining.into_iter().join("\n  ")
+                    )
+                } else {
+                    String::new()
+                }
+            };
+
             transmit(
                 opts.gctx,
                 ws,
@@ -244,6 +258,7 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
                 &mut registry,
                 source_ids.original,
                 opts.dry_run,
+                workspace_context,
             )?;
             to_confirm.insert(pkg_id);
 
@@ -632,6 +647,7 @@ fn transmit(
     registry: &mut Registry,
     registry_id: SourceId,
     dry_run: bool,
+    workspace_context: impl Fn() -> String,
 ) -> CargoResult<()> {
     let new_crate = prepare_transmit(gctx, ws, pkg, registry_id)?;
 
@@ -641,9 +657,15 @@ fn transmit(
         return Ok(());
     }
 
-    let warnings = registry
+    let warnings = registry.publish(&new_crate, tarball).with_context(|| {
-        .publish(&new_crate, tarball)
+        format!(
-        .with_context(|| format!("failed to publish to registry at {}", registry.host()))?;
+            "failed to publish {} v{} to registry at {}{}",
+            pkg.name(),
+            pkg.version(),
+            registry.host(),
+            workspace_context()
+        )
+    })?;
 
     if !warnings.invalid_categories.is_empty() {
         let msg = format!(

tests/testsuite/publish.rs

@@ -2260,7 +2260,7 @@ fn api_error_json() {
 [PACKAGING] foo v0.0.1 ([ROOT]/foo)
 [PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 [UPLOADING] foo v0.0.1 ([ROOT]/foo)
-[ERROR] failed to publish to registry at http://127.0.0.1:[..]/
+[ERROR] failed to publish foo v0.0.1 to registry at http://127.0.0.1:[..]/
 
 Caused by:
   the remote server responded with an error (status 403 Forbidden): you must be logged in
@@ -2308,7 +2308,7 @@ fn api_error_200() {
 [PACKAGING] foo v0.0.1 ([ROOT]/foo)
 [PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 [UPLOADING] foo v0.0.1 ([ROOT]/foo)
-[ERROR] failed to publish to registry at http://127.0.0.1:[..]/
+[ERROR] failed to publish foo v0.0.1 to registry at http://127.0.0.1:[..]/
 
 Caused by:
   the remote server responded with an [ERROR] max upload size is 123
@@ -2356,7 +2356,7 @@ fn api_error_code() {
 [PACKAGING] foo v0.0.1 ([ROOT]/foo)
 [PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 [UPLOADING] foo v0.0.1 ([ROOT]/foo)
-[ERROR] failed to publish to registry at http://127.0.0.1:[..]/
+[ERROR] failed to publish foo v0.0.1 to registry at http://127.0.0.1:[..]/
 
 Caused by:
   failed to get a 200 OK response, got 400
@@ -2413,7 +2413,7 @@ fn api_curl_error() {
 [PACKAGING] foo v0.0.1 ([ROOT]/foo)
 [PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 [UPLOADING] foo v0.0.1 ([ROOT]/foo)
-[ERROR] failed to publish to registry at http://127.0.0.1:[..]/
+[ERROR] failed to publish foo v0.0.1 to registry at http://127.0.0.1:[..]/
 
 Caused by:
   [52] Server returned nothing (no headers, no data) (Empty reply from server)
@@ -2461,7 +2461,7 @@ fn api_other_error() {
 [PACKAGING] foo v0.0.1 ([ROOT]/foo)
 [PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 [UPLOADING] foo v0.0.1 ([ROOT]/foo)
-[ERROR] failed to publish to registry at http://127.0.0.1:[..]/
+[ERROR] failed to publish foo v0.0.1 to registry at http://127.0.0.1:[..]/
 
 Caused by:
   invalid response body from server
@@ -3608,7 +3608,7 @@ fn invalid_token() {
 [PACKAGING] foo v0.0.1 ([ROOT]/foo)
 [PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 [UPLOADING] foo v0.0.1 ([ROOT]/foo)
-[ERROR] failed to publish to registry at http://127.0.0.1:[..]/
+[ERROR] failed to publish foo v0.0.1 to registry at http://127.0.0.1:[..]/
 
 Caused by:
   token contains invalid characters.
@@ -4402,3 +4402,110 @@ See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for
 "#]])
         .run();
 }
+
+#[cargo_test]
+fn workspace_publish_rate_limit_error() {
+    let registry = registry::RegistryBuilder::new()
+        .http_api()
+        .http_index()
+        .add_responder("/api/v1/crates/new", |_req, _| {
+            // For simplicity, let's just return rate limit error for all requests
+            // This simulates hitting rate limit during workspace publish
+            Response {
+                code: 429,
+                headers: vec!["Retry-After: 3600".to_string()],
+                body: format!(
+                    "You have published too many new crates in a short period of time. Please try again after Fri, 18 Jul 2025 20:00:34 GMT or email help@crates.io to have your limit increased."
+                ).into_bytes(),
+            }
+        })
+        .build();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [workspace]
+            members = ["package_a", "package_b", "package_c"]
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "package_a/Cargo.toml",
+            r#"
+            [package]
+            name = "package_a"
+            version = "0.1.0"
+            edition = "2015"
+            license = "MIT"
+            description = "package a"
+            repository = "https://github.com/test/package_a"
+            "#,
+        )
+        .file("package_a/src/lib.rs", "")
+        .file(
+            "package_b/Cargo.toml",
+            r#"
+            [package]
+            name = "package_b"
+            version = "0.1.0"
+            edition = "2015"
+            license = "MIT"
+            description = "package b"
+            repository = "https://github.com/test/package_b"
+            "#,
+        )
+        .file("package_b/src/lib.rs", "")
+        .file(
+            "package_c/Cargo.toml",
+            r#"
+            [package]
+            name = "package_c"
+            version = "0.1.0"
+            edition = "2015"
+            license = "MIT"
+            description = "package c"
+            repository = "https://github.com/test/package_c"
+
+            [dependencies]
+            package_a = { version = "0.1.0", path = "../package_a" }
+            "#,
+        )
+        .file("package_c/src/lib.rs", "")
+        .build();
+
+    // This demonstrates the improved error message after the fix
+    // The user now knows which package failed and what packages remain to be published
+    p.cargo("publish --workspace --no-verify")
+        .replace_crates_io(registry.index_url())
+        .with_status(101)
+        .with_stderr_data(str![[r#"
+[UPDATING] crates.io index
+[PACKAGING] package_a v0.1.0 ([ROOT]/foo/package_a)
+[PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
+[PACKAGING] package_b v0.1.0 ([ROOT]/foo/package_b)
+[PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
+[PACKAGING] package_c v0.1.0 ([ROOT]/foo/package_c)
+[UPDATING] crates.io index
+[PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
+[UPLOADING] package_a v0.1.0 ([ROOT]/foo/package_a)
+[ERROR] failed to publish package_a v0.1.0 to registry at http://127.0.0.1:[..]/
+
+[NOTE] the following crates have not been published yet:
+  package_b v0.1.0 ([ROOT]/foo/package_b)
+  package_c v0.1.0 ([ROOT]/foo/package_c)
+
+Caused by:
+  failed to get a 200 OK response, got 429
+  headers:
+  	HTTP/1.1 429
+  	Content-Length: 172
+  	Connection: close
+  	Retry-After: 3600
+  	
+  body:
+  You have published too many new crates in a short period of time. Please try again after Fri, 18 Jul 2025 20:00:34 GMT or email help@crates.io to have your limit increased.
+
+"#]])
+        .run();
+}