Make maturin develop fail if version info is missing in pyproject.toml

src/develop.rs

@@ -403,6 +403,16 @@ pub fn develop(develop_options: DevelopOptions, venv_dir: &Path) -> Result<()> {
         .editable(true)
         .build()?;
 
+    // Ensure that version information is present, https://github.com/PyO3/maturin/issues/2416
+    if build_context
+        .pyproject_toml
+        .as_ref()
+        .is_some_and(|p| !p.warn_invalid_version_info())
+    {
+        bail!("Cannot build source distribution without valid version information. \
+               You need to specify either `project.version` or `project.dynamic = ['version']` in pyproject.toml.");
+    }
+
     let interpreter =
         PythonInterpreter::check_executable(&python, &target, build_context.bridge())?.ok_or_else(
             || anyhow!("Expected `python` to be a python interpreter inside a virtualenv ಠ_ಠ"),

src/metadata.rs

@@ -144,13 +144,18 @@ impl Metadata24 {
             }
 
             self.name.clone_from(&project.name);
-            if let Some(version) = &project.version {
-                if dynamic.contains("version") {
-                    eprintln!("⚠️  Warning: `project.dynamic` must not specify `version` when `project.version` is present in pyproject.toml");
+
+            let version_ok = pyproject_toml.warn_invalid_version_info();
+            if !version_ok {
+                // This is a hard error for maturin>=2.0, see https://github.com/PyO3/maturin/issues/2416.
+                let current_major = env!("CARGO_PKG_VERSION_MAJOR").parse::<usize>().unwrap();
+                if current_major > 1 {
+                    bail!("Invalid version information in pyproject.toml.");
                 }
+            }
+
+            if let Some(version) = &project.version {
                 self.version = version.clone();
-            } else if !dynamic.contains("version") {
-                eprintln!("⚠️  Warning: `project.version` field is required in pyproject.toml unless it is present in the `project.dynamic` list");
             }
 
             if let Some(description) = &project.description {

src/pyproject_toml.rs

@@ -426,6 +426,30 @@ impl PyProjectToml {
         );
         false
     }
+
+    /// Having a pyproject.toml project table with neither `version` nor `dynamic = ['version']`
+    /// violates https://packaging.python.org/en/latest/specifications/pyproject-toml/#dynamic.
+    ///
+    /// Returns true if version information is specified correctly or no project table is present.
+    pub fn warn_invalid_version_info(&self) -> bool {
+        let Some(project) = &self.project else {
+            return true;
+        };
+        let has_static_version = project.version.is_some();
+        let has_dynamic_version = project
+            .dynamic
+            .as_ref()
+            .is_some_and(|d| d.iter().any(|s| s == "version"));
+        if has_static_version && has_dynamic_version {
+            eprintln!("⚠️  Warning: `project.dynamic` must not specify `version` when `project.version` is present in pyproject.toml");
+            return false;
+        }
+        if !has_static_version && !has_dynamic_version {
+            eprintln!("⚠️  Warning: `project.version` field is required in pyproject.toml unless it is present in the `project.dynamic` list");
+            return false;
+        }
+        true
+    }
 }
 
 #[cfg(test)]
@@ -544,6 +568,62 @@ mod tests {
         assert!(!without_constraint.warn_bad_maturin_version());
     }
 
+    #[test]
+    fn test_warn_invalid_version_info_conflict() {
+        let conflict = toml::from_str::<PyProjectToml>(
+            r#"[build-system]
+            requires = ["maturin==1.0.0"]
+
+            [project]
+            name = "..."
+            version = "1.2.3"
+            dynamic = ['version']
+            "#,
+        )
+        .unwrap();
+        assert!(!conflict.warn_invalid_version_info());
+    }
+
+    #[test]
+    fn test_warn_invalid_version_info_missing() {
+        let missing = toml::from_str::<PyProjectToml>(
+            r#"[build-system]
+            requires = ["maturin==1.0.0"]
+
+            [project]
+            name = "..."
+            "#,
+        )
+        .unwrap();
+        assert!(!missing.warn_invalid_version_info());
+    }
+
+    #[test]
+    fn test_warn_invalid_version_info_ok() {
+        let static_ver = toml::from_str::<PyProjectToml>(
+            r#"[build-system]
+            requires = ["maturin==1.0.0"]
+
+            [project]
+            name = "..."
+            version = "1.2.3"
+            "#,
+        )
+        .unwrap();
+        assert!(static_ver.warn_invalid_version_info());
+        let dynamic_ver = toml::from_str::<PyProjectToml>(
+            r#"[build-system]
+            requires = ["maturin==1.0.0"]
+
+            [project]
+            name = "..."
+            dynamic = ['version']
+            "#,
+        )
+        .unwrap();
+        assert!(dynamic_ver.warn_invalid_version_info());
+    }
+
     #[test]
     fn deserialize_include_exclude() {
         let single = r#"include = ["single"]"#;