fix(toml): Default package.publish based on presence of package.version

Before the default was hardcoded to `true`.  The problem was that means
that to remove the `package.version` boilerplate, you had to add
`package.publish = false` boilerplate.

To make the errors easier to understand in this situation, I err on the
side of encouraging people to put `publish = true` in their manifests.

By making this change, we also unblock "cargo script" /
`Cargo.toml` unifying the handling of `package.publish`.

src/cargo/ops/registry/publish.rs

@@ -103,7 +103,7 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
         if allowed_registries.is_empty() {
             bail!(
                 "`{}` cannot be published.\n\
-                 `package.publish` is set to `false` or an empty list in Cargo.toml and prevents publishing.",
+                 `package.publish` is must be set to `true` or a non-empty list in Cargo.toml to publish.",
                 pkg.name(),
             );
         } else if !allowed_registries.contains(&reg_name) {

src/cargo/util/toml/mod.rs

@@ -1012,11 +1012,12 @@ impl TomlManifest {
         let publish = match publish {
             Some(VecStringOrBool::VecString(ref vecstring)) => Some(vecstring.clone()),
             Some(VecStringOrBool::Bool(false)) => Some(vec![]),
-            None | Some(VecStringOrBool::Bool(true)) => None,
+            Some(VecStringOrBool::Bool(true)) => None,
+            None => version.is_none().then_some(vec![]),
         };
 
         if version.is_none() && publish != Some(vec![]) {
-            bail!("`package.version` must be specified unless `package.publish = false`");
+            bail!("`package.version` must be specified if `package.publish = true`");
         }
 
         if summary.features().contains_key("default-features") {

src/doc/src/reference/manifest.md

@@ -109,7 +109,7 @@ resolve dependencies, and for guidelines on setting your own version. See the
 [SemVer compatibility] chapter for more details on exactly what constitutes a
 breaking change.
 
-This field is optional and defaults to `0.0.0`.
+This field is optional and defaults to `0.0.0`.  The field is required for publishing packages.
 
 [Resolver]: resolver.md
 [SemVer compatibility]: semver.md
@@ -472,23 +472,22 @@ if any of those files change.
 
 ### The `publish` field
 
-The `publish` field can be used to prevent a package from being published to a
-package registry (like *crates.io*) by mistake, for instance to keep a package
-private in a company.
-
+The `publish` field can be used to control which registries names the package
+may be published to:
 ```toml
 [package]
 # ...
-publish = false
+publish = ["some-registry-name"]
 ```
 
-The value may also be an array of strings which are registry names that are
-allowed to be published to.
-
+To prevent a package from being published to a registry (like crates.io) by mistake,
+for instance to keep a package private in a company,
+you can leave off the [`version`](#the-version-field) field.
+If you'd like to be more explicit, you can disable publishing:
 ```toml
 [package]
 # ...
-publish = ["some-registry-name"]
+publish = false
 ```
 
 If publish array contains a single registry, `cargo publish` command will use

tests/testsuite/check.rs

@@ -1506,7 +1506,6 @@ fn versionless_package() {
                 [package]
                 name = "foo"
                 description = "foo"
-                publish = false
             "#,
         )
         .file("src/lib.rs", "")

tests/testsuite/metadata.rs

@@ -4273,7 +4273,6 @@ fn versionless_packages() {
             r#"
                 [package]
                 name = "bar"
-                publish = false
 
                 [dependencies]
                 foobar = "0.0.1"
@@ -4286,7 +4285,6 @@ fn versionless_packages() {
             r#"
                 [package]
                 name = "baz"
-                publish = false
 
                 [dependencies]
                 foobar = "0.0.1"

tests/testsuite/package.rs

@@ -3105,7 +3105,6 @@ fn versionless_package() {
                 [package]
                 name = "foo"
                 description = "foo"
-                publish = false
             "#,
         )
         .file("src/main.rs", r#"fn main() { println!("hello"); }"#)

tests/testsuite/publish.rs

@@ -420,7 +420,7 @@ fn unpublishable_crate() {
         .with_stderr(
             "\
 [ERROR] `foo` cannot be published.
-`package.publish` is set to `false` or an empty list in Cargo.toml and prevents publishing.
+`package.publish` is must be set to `true` or a non-empty list in Cargo.toml to publish.
 ",
         )
         .run();
@@ -794,7 +794,7 @@ fn publish_empty_list() {
         .with_stderr(
             "\
 [ERROR] `foo` cannot be published.
-`package.publish` is set to `false` or an empty list in Cargo.toml and prevents publishing.
+`package.publish` is must be set to `true` or a non-empty list in Cargo.toml to publish.
 ",
         )
         .run();
@@ -1020,7 +1020,7 @@ fn block_publish_no_registry() {
         .with_stderr(
             "\
 [ERROR] `foo` cannot be published.
-`package.publish` is set to `false` or an empty list in Cargo.toml and prevents publishing.
+`package.publish` is must be set to `true` or a non-empty list in Cargo.toml to publish.
 ",
         )
         .run();
@@ -3027,10 +3027,8 @@ fn versionless_package() {
         .with_status(101)
         .with_stderr(
             "\
-error: failed to parse manifest at `[CWD]/Cargo.toml`
-
-Caused by:
-  `package.version` must be specified unless `package.publish = false`
+error: `foo` cannot be published.
+`package.publish` is must be set to `true` or a non-empty list in Cargo.toml to publish.
 ",
         )
         .run();