Clarify warning for using features or default-features in patch

When attempting to substitute a local version of a dependency, since the
`patch` section uses syntax similar to a dependency (and the
documentation even says "The syntax is similar to the `[dependencies]`
section", it's natural to assume that other things from `[dependencies]`
also work, such as `features` or `default-features`. Attempting to use
them produces this warning:

> patch for `crate-name-here` uses the features mechanism.
> default-features and features will not take effect because the patch dependency does not support this mechanism

The phrasing "the patch dependency does not support this mechanism"
makes it seem at first glance like `patch` just doesn't support this at
all. But the actual problem is that the user needs to move the
`features`/`default-features` keys to an entry in `dependencies`
instead.

Modify the message, to make this more obvious.

Modify the corresponding warning for `replace` as well.

Update tests accordingly.

Author: joshtriplett

src/cargo/core/registry.rs

@@ -379,11 +379,23 @@ impl<'gctx> PackageRegistry<'gctx> {
                     dep.package_name()
                 );
 
-                if dep.features().len() != 0 || !dep.uses_default_features() {
-                    self.source_config.gctx().shell().warn(format!(
-                        "patch for `{}` uses the features mechanism. \
-                        default-features and features will not take effect because the patch dependency does not support this mechanism",
-                        dep.package_name()
+                let mut unused_fields = Vec::new();
+                if dep.features().len() != 0 {
+                    unused_fields.push("`features`");
+                }
+                if !dep.uses_default_features() {
+                    unused_fields.push("`default-features`")
+                }
+                if !unused_fields.is_empty() {
+                    let mut shell = self.source_config.gctx().shell();
+                    shell.warn(format!(
+                        "unused field in patch for `{}`: {}",
+                        dep.package_name(),
+                        unused_fields.join(", ")
+                    ))?;
+                    shell.note(format!(
+                        "configure {} in the `dependencies` entry",
+                        unused_fields.join(", ")
                     ))?;
                 }
 

src/cargo/ops/resolve.rs

@@ -209,14 +209,24 @@ pub fn resolve_ws_with_opts<'gctx>(
                     .warn(format!("package replacement is not used: {}", replace_spec))?
             }
 
-            if dep.features().len() != 0 || !dep.uses_default_features() {
-                ws.gctx()
-                .shell()
-                .warn(format!(
-                    "replacement for `{}` uses the features mechanism. \
-                    default-features and features will not take effect because the replacement dependency does not support this mechanism",
-                    dep.package_name()
-                ))?
+            let mut unused_fields = Vec::new();
+            if dep.features().len() != 0 {
+                unused_fields.push("`features`");
+            }
+            if !dep.uses_default_features() {
+                unused_fields.push("`default-features`")
+            }
+            if !unused_fields.is_empty() {
+                let mut shell = ws.gctx().shell();
+                shell.warn(format!(
+                    "unused field in replacement for `{}`: {}",
+                    dep.package_name(),
+                    unused_fields.join(", ")
+                ))?;
+                shell.note(format!(
+                    "configure {} in the `dependencies` entry",
+                    unused_fields.join(", ")
+                ))?;
             }
         }
 

tests/testsuite/patch.rs

@@ -928,20 +928,26 @@ fn add_patch_with_features() {
         .file("bar/src/lib.rs", r#""#)
         .build();
 
-    p.cargo("check").with_stderr_data(str![[r#"
-[WARNING] patch for `bar` uses the features mechanism. default-features and features will not take effect because the patch dependency does not support this mechanism
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
+[WARNING] unused field in patch for `bar`: `features`
+[NOTE] configure `features` in the `dependencies` entry
 [UPDATING] `dummy-registry` index
 [LOCKING] 1 package to latest compatible version
 [CHECKING] bar v0.1.0 ([ROOT]/foo/bar)
 [CHECKING] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
-"#]]).run();
-    p.cargo("check").with_stderr_data(str![[r#"
-[WARNING] patch for `bar` uses the features mechanism. default-features and features will not take effect because the patch dependency does not support this mechanism
+"#]])
+        .run();
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
+[WARNING] unused field in patch for `bar`: `features`
+[NOTE] configure `features` in the `dependencies` entry
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
-"#]]).run();
+"#]])
+        .run();
 }
 
 #[cargo_test]
@@ -970,20 +976,26 @@ fn add_patch_with_setting_default_features() {
         .file("bar/src/lib.rs", r#""#)
         .build();
 
-    p.cargo("check").with_stderr_data(str![[r#"
-[WARNING] patch for `bar` uses the features mechanism. default-features and features will not take effect because the patch dependency does not support this mechanism
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
+[WARNING] unused field in patch for `bar`: `features`, `default-features`
+[NOTE] configure `features`, `default-features` in the `dependencies` entry
 [UPDATING] `dummy-registry` index
 [LOCKING] 1 package to latest compatible version
 [CHECKING] bar v0.1.0 ([ROOT]/foo/bar)
 [CHECKING] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
-"#]]).run();
-    p.cargo("check").with_stderr_data(str![[r#"
-[WARNING] patch for `bar` uses the features mechanism. default-features and features will not take effect because the patch dependency does not support this mechanism
+"#]])
+        .run();
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
+[WARNING] unused field in patch for `bar`: `features`, `default-features`
+[NOTE] configure `features`, `default-features` in the `dependencies` entry
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
-"#]]).run();
+"#]])
+        .run();
 }
 
 #[cargo_test]

tests/testsuite/replace.rs

@@ -89,16 +89,19 @@ fn override_with_features() {
         )
         .build();
 
-    p.cargo("check").with_stderr_data(str![[r#"
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
 [UPDATING] `dummy-registry` index
 [UPDATING] git repository `[ROOTURL]/override`
 [LOCKING] 2 packages to latest compatible versions
-[WARNING] replacement for `bar` uses the features mechanism. default-features and features will not take effect because the replacement dependency does not support this mechanism
+[WARNING] unused field in replacement for `bar`: `features`
+[NOTE] configure `features` in the `dependencies` entry
 [CHECKING] bar v0.1.0 ([ROOTURL]/override#[..])
 [CHECKING] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
-"#]]).run();
+"#]])
+        .run();
 }
 
 #[cargo_test]
@@ -136,16 +139,19 @@ fn override_with_setting_default_features() {
         )
         .build();
 
-    p.cargo("check").with_stderr_data(str![[r#"
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
 [UPDATING] `dummy-registry` index
 [UPDATING] git repository `[ROOTURL]/override`
 [LOCKING] 2 packages to latest compatible versions
-[WARNING] replacement for `bar` uses the features mechanism. default-features and features will not take effect because the replacement dependency does not support this mechanism
+[WARNING] unused field in replacement for `bar`: `features`, `default-features`
+[NOTE] configure `features`, `default-features` in the `dependencies` entry
 [CHECKING] bar v0.1.0 ([ROOTURL]/override#[..])
 [CHECKING] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
-"#]]).run();
+"#]])
+        .run();
 }
 
 #[cargo_test]