docs(ref): Re-org workspace docs to be like package docs

In looking over rust-lang#10625, I remembered we've been having growing pains
with the workspace documentation.  It was originally written when there
were a lot fewer workspace features.  As more workspace features have
been added, they've been tacked on to the documentation.

This re-thinks the documentation by focusing on the schema, much like
`manifest.md` does.

Author: epage

src/doc/src/reference/manifest.md

@@ -516,7 +516,7 @@ external tools may wish to use them in a consistent fashion, such as referring
 to the data in `workspace.metadata` if data is missing from `package.metadata`,
 if that makes sense for the tool in question.
 
-[workspace-metadata]: workspaces.md#the-workspacemetadata-table
+[workspace-metadata]: workspaces.md#the-metadata-table
 
 #### The `default-run` field
 

src/doc/src/reference/specifying-dependencies.md

@@ -489,7 +489,7 @@ rand = { workspace = true, optional = true }
 
 [crates.io]: https://crates.io/
 [dev-dependencies]: #development-dependencies
-[workspace.dependencies]: workspaces.md#the-workspacedependencies-table
+[workspace.dependencies]: workspaces.md#the-dependencies-table
 [optional]: features.md#optional-dependencies
 [features]: features.md
 

src/doc/src/reference/unstable.md

@@ -1358,7 +1358,7 @@ for more information.
 ### Workspace Inheritance
 
 Workspace Inheritance has been stabilized in the 1.64 release.
-See [workspace.package](workspaces.md#the-workspacepackage-table), 
-[workspace.dependencies](workspaces.md#the-workspacedependencies-table), 
+See [workspace.package](workspaces.md#the-package-table), 
+[workspace.dependencies](workspaces.md#the-dependencies-table), 
 and [inheriting-a-dependency-from-a-workspace](specifying-dependencies.md#inheriting-a-dependency-from-a-workspace)
-for more information.
+for more information.

src/doc/src/reference/workspaces.md

@@ -3,39 +3,79 @@
 A *workspace* is a collection of one or more packages that share common
 dependency resolution (with a shared `Cargo.lock`), output directory, and
 various settings such as profiles. Packages that are part of a workspaces are
-called *workspace members*. There are two flavours of workspaces: as root
-package or as virtual manifest.
+called *workspace members*.
 
-### Root package
+The key points of workspaces are:
+
+* All packages share a common `Cargo.lock` file which resides in the
+  *workspace root*.
+* All packages share a common [output directory], which defaults to a
+  directory named `target` in the *workspace root*.
+* The [`[patch]`][patch], [`[replace]`][replace] and [`[profile.*]`][profiles]
+  sections in `Cargo.toml` are only recognized in the *root* manifest, and
+  ignored in member crates' manifests.
 
-A workspace can be created by adding a [`[workspace]`
-section](#the-workspace-section) to `Cargo.toml`. This can be added to a
-`Cargo.toml` that already defines a `[package]`, in which case the package is
+In the `Cargo.toml`, the `[workspace]` table supports the following sections:
+
+* [`[workspace]`](#the-workspace-section) — Defines a workspace.
+  * [`members`](#the-members-and-exclude-fields) — Packages to include in the workspace.
+  * [`exclude`](#the-members-and-exclude-fields) — Packages to exclude from the workspace.
+  * [`default-members`](#the-default-members-field) — Packages to operate on when a specific package wasn't selected.
+  * [`metadata`](#the-metadata-table) — Extra settings for external tools.
+  * [`package`](#the-package-table) — Keys for inheriting in packages.
+  * [`dependencies`](#the-dependencies-table) — Keys for inheriting in package dependencies.
+
+### The `[workspace]` section
+
+To create a workspace, you add the `[workspace]` table to a `Cargo.toml`:
+```toml
+[workspace]
+# ...
+```
+
+At minimum, a workspace has to have a member, either with a root package or as
+a virtual manifest.
+
+#### Root package
+
+If the [`[workspace]` section](#the-workspace-section) is added to a
+`Cargo.toml` that already defines a `[package]`, the package is
 the *root package* of the workspace. The *workspace root* is the directory
 where the workspace's `Cargo.toml` is located.
 
-### Virtual manifest
+```toml
+[workspace]
+
+[package]
+name = "hello_world" # the name of the package
+version = "0.1.0"    # the current version, obeying semver
+authors = ["Alice <[email protected]>", "Bob <[email protected]>"]
+```
+
+#### Virtual workspace
 
 Alternatively, a `Cargo.toml` file can be created with a `[workspace]` section
 but without a [`[package]` section][package]. This is called a *virtual
 manifest*. This is typically useful when there isn't a "primary" package, or
 you want to keep all the packages organized in separate directories.
 
-### Key features
-
-The key points of workspaces are:
+```toml
+# [PROJECT_DIR]/Cargo.toml
+[workspace]
+members = ["hello_world"]
+```
 
-* All packages share a common `Cargo.lock` file which resides in the
-  *workspace root*.
-* All packages share a common [output directory], which defaults to a
-  directory named `target` in the *workspace root*.
-* The [`[patch]`][patch], [`[replace]`][replace] and [`[profile.*]`][profiles]
-  sections in `Cargo.toml` are only recognized in the *root* manifest, and
-  ignored in member crates' manifests.
+```toml
+# [PROJECT_DIR]/hello_world/Cargo.toml
+[package]
+name = "hello_world" # the name of the package
+version = "0.1.0"    # the current version, obeying semver
+authors = ["Alice <[email protected]>", "Bob <[email protected]>"]
+```
 
-### The `[workspace]` section
+### The `members` and `exclude` fields 
 
-The `[workspace]` table in `Cargo.toml` defines which packages are members of
+The `members` and `exclude` fields define which packages are members of
 the workspace:
 
 ```toml
@@ -56,26 +96,24 @@ workspace. This can be useful if some path dependencies aren't desired to be
 in the workspace at all, or using a glob pattern and you want to remove a
 directory.
 
-An empty `[workspace]` table can be used with a `[package]` to conveniently
-create a workspace with the package and all of its path dependencies.
-
-### Workspace selection
-
 When inside a subdirectory within the workspace, Cargo will automatically
 search the parent directories for a `Cargo.toml` file with a `[workspace]`
 definition to determine which workspace to use. The [`package.workspace`]
 manifest key can be used in member crates to point at a workspace's root to
 override this automatic search. The manual setting can be useful if the member
 is not inside a subdirectory of the workspace root.
 
-### Package selection
+#### Package Selection
 
 In a workspace, package-related cargo commands like [`cargo build`] can use
 the `-p` / `--package` or `--workspace` command-line flags to determine which
 packages to operate on. If neither of those flags are specified, Cargo will
 use the package in the current working directory. If the current directory is
-a virtual workspace, it will apply to all members (as if `--workspace` were
-specified on the command-line).
+a [virtual workspace](#virtual-workspace), it will apply to all members (as if
+`--workspace` were specified on the command-line).  See also
+[`default-members`](#the-default-members-field).
+
+### The `default-members` field
 
 The optional `default-members` key can be specified to set the members to
 operate on when in the workspace root and the package selection flags are not
@@ -89,7 +127,7 @@ default-members = ["path/to/member2", "path/to/member3/foo"]
 
 When specified, `default-members` must expand to a subset of `members`.
 
-### The `workspace.metadata` table
+### The `metadata` table
 
 The `workspace.metadata` table is ignored by Cargo and will not be warned
 about. This section can be used for tools that would like to store workspace
@@ -112,7 +150,7 @@ external tools may wish to use them in a consistent fashion, such as referring
 to the data in `workspace.metadata` if data is missing from `package.metadata`,
 if that makes sense for the tool in question.
 
-### The `workspace.package` table
+### The `package` table
 
 The `workspace.package` table is where you define keys that can be
 inherited by members of a workspace. These keys can be inherited by
@@ -157,7 +195,7 @@ description.workspace = true
 documentation.workspace = true
 ```
 
-### The `workspace.dependencies` table
+### The `dependencies` table
 
 The `workspace.dependencies` table is where you define dependencies to be
 inherited by members of a workspace.