Default values for readme if not specified

crates/cargo-test-support/src/lib.rs

@@ -1622,6 +1622,24 @@ pub fn basic_lib_manifest(name: &str) -> String {
     )
 }
 
+pub fn basic_bin_manifest_with_readme(name: &str, readme_filename: &str) -> String {
+    format!(
+        r#"
+        [package]
+
+        name = "{}"
+        version = "0.5.0"
+        authors = ["[email protected]"]
+        readme = "{}"
+
+        [[bin]]
+
+        name = "{}"
+    "#,
+        name, readme_filename, name
+    )
+}
+
 pub fn path2url<P: AsRef<Path>>(p: P) -> Url {
     Url::from_file_path(p).ok().unwrap()
 }

src/cargo/util/toml/mod.rs

@@ -1198,11 +1198,12 @@ impl TomlManifest {
             project.links.as_deref(),
             project.namespaced_features.unwrap_or(false),
         )?;
+
         let metadata = ManifestMetadata {
             description: project.description.clone(),
             homepage: project.homepage.clone(),
             documentation: project.documentation.clone(),
-            readme: project.readme.clone(),
+            readme: readme_for_project(package_root, project),
             authors: project.authors.clone().unwrap_or_default(),
             license: project.license.clone(),
             license_file: project.license_file.clone(),
@@ -1513,6 +1514,43 @@ impl TomlManifest {
     }
 }
 
+/// Returns the name of the README file for a `TomlProject`.
+fn readme_for_project(package_root: &Path, project: &Box<TomlProject>) -> Option<String> {
+    match &project.readme {
+        None => default_readme_from_package_root(package_root),
+        Some(value) => match value.as_str() {
+            "false" => None,
+            _ => Some(value.clone()),
+        },
+    }
+}
+
+const DEFAULT_README_FILES: [&str; 3] = ["README.md", "README.txt", "README"];
+
+/// Checks if a file with any of the default README file names exists in the package root.
+/// If so, returns a `String` representing that name.
+fn default_readme_from_package_root(package_root: &Path) -> Option<String> {
+    _default_readme_from_package_root(package_root).ok()
+}
+
+fn _default_readme_from_package_root(package_root: &Path) -> CargoResult<String> {
+    for entry in package_root.read_dir()? {
+        let entry = entry?;
+
+        let fname = entry.file_name();
+
+        if entry.metadata()?.is_file() && DEFAULT_README_FILES.contains(&fname.to_str().unwrap()) {
+            return Ok(fname
+                .into_string()
+                .map_err(|_| anyhow!("Could not convert the README's file name into a String"))?);
+        }
+    }
+
+    Err(anyhow!(
+        "No files with the default README file names found in the package root."
+    ))
+}
+
 /// Checks a list of build targets, and ensures the target names are unique within a vector.
 /// If not, the name of the offending build target is returned.
 fn unique_build_targets(targets: &[Target], package_root: &Path) -> Result<(), String> {

src/doc/src/reference/manifest.md

@@ -165,6 +165,11 @@ will interpret it as Markdown and render it on the crate's page.
 readme = "README.md"
 ```
 
+If no value is specified for this field, and a file named `README.md`,
+`README.txt` or `README` exists in the package root, then the name of that
+file will be used. You can suppress this behavior by setting this field to
+`"false"`.
+
 #### The `homepage` field
 
 The `homepage` field should be a URL to a site that is the home page for your

tests/testsuite/read_manifest.rs

@@ -1,15 +1,17 @@
 //! Tests for the `cargo read-manifest` command.
 
-use cargo_test_support::{basic_bin_manifest, main_file, project};
+use cargo_test_support::{basic_bin_manifest, basic_bin_manifest_with_readme, main_file, project};
 
-static MANIFEST_OUTPUT: &str = r#"
-{
+fn manifest_output(readme_value: &str) -> String {
+    format!(
+        r#"
+{{
     "authors": [
         "[email protected]"
     ],
     "categories": [],
     "name":"foo",
-    "readme": null,
+    "readme": {},
     "repository": null,
     "version":"0.5.0",
     "id":"foo[..]0.5.0[..](path+file://[..]/foo)",
@@ -21,19 +23,26 @@ static MANIFEST_OUTPUT: &str = r#"
     "edition": "2015",
     "source":null,
     "dependencies":[],
-    "targets":[{
+    "targets":[{{
         "kind":["bin"],
         "crate_types":["bin"],
         "doctest": false,
         "edition": "2015",
         "name":"foo",
         "src_path":"[..]/foo/src/foo.rs"
-    }],
-    "features":{},
+    }}],
+    "features":{{}},
     "manifest_path":"[..]Cargo.toml",
     "metadata": null,
     "publish": null
-}"#;
+}}"#,
+        readme_value
+    )
+}
+
+fn manifest_output_no_readme() -> String {
+    manifest_output("null")
+}
 
 #[cargo_test]
 fn cargo_read_manifest_path_to_cargo_toml_relative() {
@@ -44,7 +53,7 @@ fn cargo_read_manifest_path_to_cargo_toml_relative() {
 
     p.cargo("read-manifest --manifest-path foo/Cargo.toml")
         .cwd(p.root().parent().unwrap())
-        .with_json(MANIFEST_OUTPUT)
+        .with_json(&manifest_output_no_readme())
         .run();
 }
 
@@ -58,7 +67,7 @@ fn cargo_read_manifest_path_to_cargo_toml_absolute() {
     p.cargo("read-manifest --manifest-path")
         .arg(p.root().join("Cargo.toml"))
         .cwd(p.root().parent().unwrap())
-        .with_json(MANIFEST_OUTPUT)
+        .with_json(&manifest_output_no_readme())
         .run();
 }
 
@@ -104,5 +113,40 @@ fn cargo_read_manifest_cwd() {
         .file("src/foo.rs", &main_file(r#""i am foo""#, &[]))
         .build();
 
-    p.cargo("read-manifest").with_json(MANIFEST_OUTPUT).run();
+    p.cargo("read-manifest")
+        .with_json(&manifest_output_no_readme())
+        .run();
+}
+
+#[cargo_test]
+fn cargo_read_manifest_default_readme() {
+    let readme_filenames = ["README.md", "README.txt", "README"];
+
+    for readme in readme_filenames.iter() {
+        let p = project()
+            .file("Cargo.toml", &basic_bin_manifest("foo"))
+            .file(readme, "Sample project")
+            .file("src/foo.rs", &main_file(r#""i am foo""#, &[]))
+            .build();
+
+        p.cargo("read-manifest")
+            .with_json(&manifest_output(&format!(r#""{}""#, readme)))
+            .run();
+    }
+}
+
+#[cargo_test]
+fn cargo_read_manifest_suppress_default_readme() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            &basic_bin_manifest_with_readme("foo", "false"),
+        )
+        .file("README.txt", "Sample project")
+        .file("src/foo.rs", &main_file(r#""i am foo""#, &[]))
+        .build();
+
+    p.cargo("read-manifest")
+        .with_json(&manifest_output_no_readme())
+        .run();
 }