Improve error message when using API command with non-remote registry.

src/cargo/core/source/source_id.rs

@@ -259,6 +259,17 @@ impl SourceId {
         }
     }
 
+    /// Returns `true` if this source is a "remote" registry.
+    ///
+    /// "remote" may also mean a file URL to a git index, so it is not
+    /// necessarily "remote". This just means it is not `local-registry`.
+    pub fn is_remote_registry(self) -> bool {
+        match self.inner.kind {
+            Kind::Registry => true,
+            _ => false,
+        }
+    }
+
     /// Returns `true` if this source from a Git repository.
     pub fn is_git(self) -> bool {
         match self.inner.kind {

src/cargo/ops/registry.rs

@@ -345,6 +345,13 @@ fn registry(
     } = registry_configuration(config, registry.clone())?;
     let token = token.or(token_config);
     let sid = get_source_id(config, index_config.or(index), registry)?;
+    if !sid.is_remote_registry() {
+        bail!(
+            "{} does not support API commands.\n\
+             Check for a source-replacement in .cargo/config.",
+            sid
+        );
+    }
     let api_host = {
         let _lock = config.acquire_package_cache_lock()?;
         let mut src = RegistrySource::remote(sid, &HashSet::new(), config);

tests/testsuite/publish.rs

@@ -1022,3 +1022,51 @@ fn publish_checks_for_token_before_verify() {
         .with_stderr_contains("[VERIFYING] foo v0.0.1 ([CWD])")
         .run();
 }
+
+#[cargo_test]
+fn publish_with_bad_source() {
+    let p = project()
+        .file(
+            ".cargo/config",
+            r#"
+            [source.crates-io]
+            replace-with = 'local-registry'
+
+            [source.local-registry]
+            local-registry = 'registry'
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("publish")
+        .with_status(101)
+        .with_stderr(
+            "\
+[ERROR] registry `[..]/foo/registry` does not support API commands.
+Check for a source-replacement in .cargo/config.
+",
+        )
+        .run();
+
+    p.change_file(
+        ".cargo/config",
+        r#"
+        [source.crates-io]
+        replace-with = "vendored-sources"
+
+        [source.vendored-sources]
+        directory = "vendor"
+        "#,
+    );
+
+    p.cargo("publish")
+        .with_status(101)
+        .with_stderr(
+            "\
+[ERROR] dir [..]/foo/vendor does not support API commands.
+Check for a source-replacement in .cargo/config.
+",
+        )
+        .run();
+}