publish: rework the crates.io detection logic.

The old code used an unreliable method to detect if `cargo publish` was publishing to crates.io. This should work even if the `--index` flag is used.

Also includes a very minor rewording of an error message mentioning crates.io, even for alternative registries.

src/cargo/core/source/source_id.rs

@@ -248,13 +248,6 @@ impl SourceId {
         }
     }
 
-    /// Is this source from an alternative registry
-    /// DEPRECATED: This is not correct if the registry name is not known
-    /// (for example when loaded from an index).
-    pub fn is_alt_registry(self) -> bool {
-        self.is_registry() && self.inner.name.is_some()
-    }
-
     /// Is this source from a git repository
     pub fn is_git(self) -> bool {
         match self.inner.kind {

src/cargo/ops/registry.rs

@@ -68,7 +68,7 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
         opts.registry.clone(),
         true,
     )?;
-    verify_dependencies(pkg, reg_id)?;
+    verify_dependencies(pkg, &registry, reg_id)?;
 
     // Prepare a tarball, with a non-surpressable warning if metadata
     // is missing since this is being put online.
@@ -102,7 +102,11 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
     Ok(())
 }
 
-fn verify_dependencies(pkg: &Package, registry_src: SourceId) -> CargoResult<()> {
+fn verify_dependencies(
+    pkg: &Package,
+    registry: &Registry,
+    registry_src: SourceId,
+) -> CargoResult<()> {
     for dep in pkg.dependencies().iter() {
         if dep.source_id().is_path() {
             if !dep.specified_req() {
@@ -115,9 +119,16 @@ fn verify_dependencies(pkg: &Package, registry_src: SourceId) -> CargoResult<()>
             }
         } else if dep.source_id() != registry_src {
             if dep.source_id().is_registry() {
-                // Block requests to send to a registry if it is not an alternative
-                // registry
-                if !registry_src.is_alt_registry() {
+                // Block requests to send to crates.io with alt-registry deps.
+                // This extra hostname check is mostly to assist with testing,
+                // but also prevents someone using `--index` to specify
+                // something that points to crates.io.
+                let is_crates_io = registry
+                    .host()
+                    .to_url()
+                    .map(|u| u.host_str() == Some("crates.io"))
+                    .unwrap_or(false);
+                if registry_src.is_default_registry() || is_crates_io {
                     failure::bail!("crates cannot be published to crates.io with dependencies sourced from other\n\
                            registries either publish `{}` on crates.io or pull it into this repository\n\
                            and specify it with a path and version\n\
@@ -128,9 +139,9 @@ fn verify_dependencies(pkg: &Package, registry_src: SourceId) -> CargoResult<()>
                 }
             } else {
                 failure::bail!(
-                    "crates cannot be published to crates.io with dependencies sourced from \
-                     a repository\neither publish `{}` as its own crate on crates.io and \
-                     specify a crates.io version as a dependency or pull it into this \
+                    "crates cannot be published with dependencies sourced from \
+                     a repository\neither publish `{}` as its own crate and \
+                     specify a version as a dependency or pull it into this \
                      repository and specify it with a path and version\n(crate `{}` has \
                      repository path `{}`)",
                     dep.package_name(),

tests/testsuite/alt_registry.rs

@@ -1,6 +1,7 @@
 use crate::support::publish::validate_alt_upload;
 use crate::support::registry::{self, Package};
 use crate::support::{basic_manifest, git, paths, project};
+use cargo::util::ToUrl;
 use std::fs::{self, File};
 use std::io::Write;
 
@@ -288,6 +289,8 @@ fn registry_incompatible_with_git() {
 
 #[test]
 fn cannot_publish_to_crates_io_with_registry_dependency() {
+    let fakeio_path = paths::root().join("fake.io");
+    let fakeio_url = fakeio_path.to_url().unwrap();
     let p = project()
         .file(
             "Cargo.toml",
@@ -303,12 +306,39 @@ fn cannot_publish_to_crates_io_with_registry_dependency() {
         "#,
         )
         .file("src/main.rs", "fn main() {}")
+        .file(
+            ".cargo/config",
+            &format!(
+                r#"
+            [registries.fakeio]
+            index = "{}"
+        "#,
+                fakeio_url
+            ),
+        )
         .build();
 
     Package::new("bar", "0.0.1").alternative(true).publish();
 
+    // Since this can't really call plain `publish` without fetching the real
+    // crates.io index, create a fake one that points to the real crates.io.
+    git::repo(&fakeio_path)
+        .file(
+            "config.json",
+            r#"
+            {"dl": "https://crates.io/api/v1/crates", "api": "https://crates.io"}
+        "#,
+        )
+        .build();
+
+    p.cargo("publish --registry fakeio -Z unstable-options")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr_contains("[ERROR] crates cannot be published to crates.io[..]")
+        .run();
+
     p.cargo("publish --index")
-        .arg(registry::registry().to_string())
+        .arg(fakeio_url.to_string())
         .masquerade_as_nightly_cargo()
         .with_status(101)
         .with_stderr_contains("[ERROR] crates cannot be published to crates.io[..]")

tests/testsuite/publish.rs

@@ -273,9 +273,9 @@ fn git_deps() {
         .with_stderr(
             "\
 [UPDATING] [..] index
-[ERROR] crates cannot be published to crates.io with dependencies sourced from \
-a repository\neither publish `foo` as its own crate on crates.io and \
-specify a crates.io version as a dependency or pull it into this \
+[ERROR] crates cannot be published with dependencies sourced from \
+a repository\neither publish `foo` as its own crate and \
+specify a version as a dependency or pull it into this \
 repository and specify it with a path and version\n\
 (crate `foo` has repository path `git://path/to/nowhere`)\
 ",