fix(add): Report a missing source error for workspace dependencies (#16063)

### What does this PR try to resolve?

When you have
```toml
[workspace.dependencies]
apply.workspace = true
```
You have a source-less workspace dependency with an unused `workspace`
field.

In #13775, we removed support for source-less dependencies but missed
this case.
This mirrors the error message from `toml/mod.rs` that #13775 added.

Other options I considered:
- Making the presence of `workspace` an error in `cargo-util-schemas`
- Validating `workspace.dependencies` in `toml/mod.rs`, even when its
not inherited

In both cases, they are behavior changes that and I wanted to keep the
focus of this change small rather than get tied up in what behavior
changes are safe or should be done with an Edition.

The second option could still lead to this panic if we move some of that
error reporting into later stages of Cargo.

Fixes #1398

### How to test and review this PR?

Author: epage

src/cargo/ops/cargo_add/mod.rs

@@ -647,7 +647,11 @@ fn query_dependency(
             let query = dep.query(gctx)?;
             match query {
                 MaybeWorkspace::Workspace(_) => {
-                    unreachable!("This should have been caught when parsing a workspace root")
+                    anyhow::bail!(
+                        "dependency ({}) specified without \
+                        providing a local path, Git repository, or version",
+                        dependency.toml_key()
+                    );
                 }
                 MaybeWorkspace::Other(query) => query,
             }

src/cargo/util/toml_mut/dependency.rs

@@ -245,91 +245,87 @@ impl Dependency {
                 (key.to_owned(), None)
             };
 
-            let source: Source = if let Some(git) = table.get("git") {
-                let mut src = GitSource::new(
-                    git.as_str()
-                        .ok_or_else(|| invalid_type(key, "git", git.type_name(), "string"))?,
-                );
-                if let Some(value) = table.get("branch") {
-                    src =
-                        src.set_branch(value.as_str().ok_or_else(|| {
+            let source: Source =
+                if let Some(git) = table.get("git") {
+                    let mut src = GitSource::new(
+                        git.as_str()
+                            .ok_or_else(|| invalid_type(key, "git", git.type_name(), "string"))?,
+                    );
+                    if let Some(value) = table.get("branch") {
+                        src = src.set_branch(value.as_str().ok_or_else(|| {
                             invalid_type(key, "branch", value.type_name(), "string")
                         })?);
-                }
-                if let Some(value) = table.get("tag") {
-                    src =
-                        src.set_tag(value.as_str().ok_or_else(|| {
+                    }
+                    if let Some(value) = table.get("tag") {
+                        src = src.set_tag(value.as_str().ok_or_else(|| {
                             invalid_type(key, "tag", value.type_name(), "string")
                         })?);
-                }
-                if let Some(value) = table.get("rev") {
-                    src =
-                        src.set_rev(value.as_str().ok_or_else(|| {
+                    }
+                    if let Some(value) = table.get("rev") {
+                        src = src.set_rev(value.as_str().ok_or_else(|| {
                             invalid_type(key, "rev", value.type_name(), "string")
                         })?);
-                }
-                if let Some(value) = table.get("version") {
-                    src = src.set_version(value.as_str().ok_or_else(|| {
-                        invalid_type(key, "version", value.type_name(), "string")
-                    })?);
-                }
-                src.into()
-            } else if let Some(path) = table.get("path") {
-                let base = table
-                    .get("base")
-                    .map(|base| {
-                        base.as_str()
-                            .ok_or_else(|| invalid_type(key, "base", base.type_name(), "string"))
-                            .map(|s| s.to_owned())
-                    })
-                    .transpose()?;
-                let relative_to = if let Some(base) = &base {
-                    Cow::Owned(lookup_path_base(
-                        &PathBaseName::new(base.clone())?,
-                        gctx,
-                        &|| Ok(workspace_root),
-                        unstable_features,
-                    )?)
-                } else {
-                    Cow::Borrowed(crate_root)
-                };
-                let path =
-                    relative_to
+                    }
+                    if let Some(value) = table.get("version") {
+                        src = src.set_version(value.as_str().ok_or_else(|| {
+                            invalid_type(key, "version", value.type_name(), "string")
+                        })?);
+                    }
+                    src.into()
+                } else if let Some(path) = table.get("path") {
+                    let base = table
+                        .get("base")
+                        .map(|base| {
+                            base.as_str()
+                                .ok_or_else(|| {
+                                    invalid_type(key, "base", base.type_name(), "string")
+                                })
+                                .map(|s| s.to_owned())
+                        })
+                        .transpose()?;
+                    let relative_to = if let Some(base) = &base {
+                        Cow::Owned(lookup_path_base(
+                            &PathBaseName::new(base.clone())?,
+                            gctx,
+                            &|| Ok(workspace_root),
+                            unstable_features,
+                        )?)
+                    } else {
+                        Cow::Borrowed(crate_root)
+                    };
+                    let path = relative_to
                         .join(path.as_str().ok_or_else(|| {
                             invalid_type(key, "path", path.type_name(), "string")
                         })?);
-                let mut src = PathSource::new(path);
-                src.base = base;
-                if let Some(value) = table.get("version") {
-                    src = src.set_version(value.as_str().ok_or_else(|| {
-                        invalid_type(key, "version", value.type_name(), "string")
-                    })?);
-                }
-                src.into()
-            } else if let Some(version) = table.get("version") {
-                let src =
-                    RegistrySource::new(version.as_str().ok_or_else(|| {
+                    let mut src = PathSource::new(path);
+                    src.base = base;
+                    if let Some(value) = table.get("version") {
+                        src = src.set_version(value.as_str().ok_or_else(|| {
+                            invalid_type(key, "version", value.type_name(), "string")
+                        })?);
+                    }
+                    src.into()
+                } else if let Some(version) = table.get("version") {
+                    let src = RegistrySource::new(version.as_str().ok_or_else(|| {
                         invalid_type(key, "version", version.type_name(), "string")
                     })?);
-                src.into()
-            } else if let Some(workspace) = table.get("workspace") {
-                let workspace_bool = workspace
-                    .as_bool()
-                    .ok_or_else(|| invalid_type(key, "workspace", workspace.type_name(), "bool"))?;
-                if !workspace_bool {
-                    anyhow::bail!("`{key}.workspace = false` is unsupported")
-                }
-                let src = WorkspaceSource::new();
-                src.into()
-            } else {
-                let mut msg = format!("unrecognized dependency source for `{key}`");
-                if table.is_empty() {
-                    msg.push_str(
-                        ", expected a local path, Git repository, version, or workspace dependency to be specified",
+                    src.into()
+                } else if let Some(workspace) = table.get("workspace") {
+                    let workspace_bool = workspace.as_bool().ok_or_else(|| {
+                        invalid_type(key, "workspace", workspace.type_name(), "bool")
+                    })?;
+                    if !workspace_bool {
+                        anyhow::bail!("`{key}.workspace = false` is unsupported")
+                    }
+                    let src = WorkspaceSource::new();
+                    src.into()
+                } else {
+                    anyhow::bail!(
+                        "dependency ({key}) specified without \
+                        providing a local path, Git repository, version, or \
+                        workspace dependency to use"
                     );
-                }
-                anyhow::bail!(msg);
-            };
+                };
             let registry = if let Some(value) = table.get("registry") {
                 Some(
                     value

tests/testsuite/cargo_add/invalid_inherited_dependency/in/Cargo.toml

@@ -0,0 +1,5 @@
+[workspace]
+members = ["primary", "dependency"]
+
+[workspace.dependencies]
+foo.workspace = true

tests/testsuite/cargo_add/invalid_inherited_dependency/in/dependency/Cargo.toml

@@ -0,0 +1,4 @@
+[package]
+name = "foo"
+version = "0.0.0"
+edition = "2015"

tests/testsuite/cargo_add/invalid_inherited_dependency/in/dependency/src/lib.rs

@@ -0,0 +1,4 @@
+[package]
+name = "bar"
+version = "0.0.0"
+edition = "2015"

tests/testsuite/cargo_add/invalid_inherited_dependency/in/primary/Cargo.toml

@@ -0,0 +1,25 @@
+use crate::prelude::*;
+use cargo_test_support::Project;
+use cargo_test_support::compare::assert_ui;
+use cargo_test_support::current_dir;
+use cargo_test_support::file;
+use cargo_test_support::str;
+
+#[cargo_test]
+fn case() {
+    cargo_test_support::registry::init();
+    let project = Project::from_template(current_dir!().join("in"));
+    let project_root = project.root();
+    let cwd = &project_root;
+
+    snapbox::cmd::Command::cargo_ui()
+        .arg("add")
+        .args(["foo", "-p", "bar"])
+        .current_dir(cwd)
+        .assert()
+        .failure()
+        .stdout_eq(str![""])
+        .stderr_eq(file!["stderr.term.svg"]);
+
+    assert_ui().subset_matches(current_dir!().join("out"), &project_root);
+}

tests/testsuite/cargo_add/invalid_inherited_dependency/in/primary/src/lib.rs

@@ -0,0 +1,5 @@
+[workspace]
+members = ["primary", "dependency"]
+
+[workspace.dependencies]
+foo.workspace = true

tests/testsuite/cargo_add/invalid_inherited_dependency/mod.rs

@@ -0,0 +1,4 @@
+[package]
+name = "foo"
+version = "0.0.0"
+edition = "2015"