Auto merge of #6535 - jethrogb:patch-section-check, r=alexcrichton

Having a [patch] section when publishing is not an error

It is not necessary to throw an error when your `Cargo.toml` has a `[patch]` section.

1. Cargo will normalize your `Cargo.toml` while packaging, which will remove the `[patch]` section.
2. Even if the `[patch]` section were to somehow get to crates.io, it would be ignored when the crate is used since only the top-level crate's `[patch]` section is used.

The current behavior is quite annoying for crate maintainers who need a permanent `[patch]` section, for example, [`rand`](rust-random/rand#670 (comment)). This is the situation that leads to rand needing a permanent `[patch]` section:

![image](https://user-images.githubusercontent.com/1132307/50951760-54cf3a00-14d4-11e9-8064-a7def2ed402f.png)

Here, `rand` and `rand_core` are in the same repository, and `rdrand` is in a separate repository. When building `rand` as the top-level crate (e.g. in CI), the `rand->rand_core` path dependency will be used. This is of course a different crate than the crates.io rand_core used by `rdrand`. Therefore, when building `rand` as a top-level crate, you will *always* need to patch `crates-io.rand` to the path dependency. When building `rand` as a dependency, there are no issues, as the crates.io crates are used everywhere.

src/cargo/ops/registry.rs

@@ -60,10 +60,6 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
         }
     }
 
-    if !pkg.manifest().patch().is_empty() {
-        failure::bail!("published crates cannot contain [patch] sections");
-    }
-
     let (mut registry, reg_id) = registry(
         opts.config,
         opts.token.clone(),

src/doc/man/cargo-publish.adoc

@@ -19,7 +19,6 @@ registry. The default registry is https://crates.io. This performs the
 following steps:
 
 . Performs a few checks, including:
-  - No `[patch]` sections are allowed in the manifest.
   - Checks the `package.publish` key in the manifest for restrictions on which
     registries you are allowed to publish to.
 . Create a `.crate` file by following the steps in man:cargo-package[1].

tests/testsuite/publish.rs

@@ -930,17 +930,71 @@ fn publish_with_patch() {
             bar = { path = "bar" }
         "#,
         )
-        .file("src/main.rs", "extern crate bar; fn main() {}")
+        .file(
+            "src/main.rs",
+            "extern crate bar;
+             fn main() {
+                 bar::newfunc();
+             }",
+        )
         .file("bar/Cargo.toml", &basic_manifest("bar", "1.0.0"))
-        .file("bar/src/lib.rs", "")
+        .file("bar/src/lib.rs", "pub fn newfunc() {}")
         .build();
 
     // Check that it works with the patched crate.
     p.cargo("build").run();
 
+    // Check that verify fails with patched crate which has new functionality.
     p.cargo("publish --index")
         .arg(registry_url().to_string())
+        .with_stderr_contains("[..]newfunc[..]")
         .with_status(101)
-        .with_stderr_contains("[ERROR] published crates cannot contain [patch] sections")
         .run();
+
+    // Remove the usage of new functionality and try again.
+    p.change_file("src/main.rs", "extern crate bar; pub fn main() {}");
+
+    p.cargo("publish --index")
+        .arg(registry_url().to_string())
+        .run();
+
+    // Note, use of `registry` in the deps here is an artifact that this
+    // publishes to a fake, local registry that is pretending to be crates.io.
+    // Normal publishes would set it to null.
+    publish::validate_upload(
+        r#"
+        {
+          "authors": [],
+          "badges": {},
+          "categories": [],
+          "deps": [
+            {
+              "default_features": true,
+              "features": [],
+              "kind": "normal",
+              "name": "bar",
+              "optional": false,
+              "registry": "https://github.com/rust-lang/crates.io-index",
+              "target": null,
+              "version_req": "^1.0"
+            }
+          ],
+          "description": "foo",
+          "documentation": null,
+          "features": {},
+          "homepage": null,
+          "keywords": [],
+          "license": "MIT",
+          "license_file": null,
+          "links": null,
+          "name": "foo",
+          "readme": null,
+          "readme_file": null,
+          "repository": null,
+          "vers": "0.0.1"
+          }
+        "#,
+        "foo-0.0.1.crate",
+        &["Cargo.toml", "Cargo.toml.orig", "src/main.rs"],
+    );
 }