From f5dd0f9c034276aeb57ff6bc381250081457db0a Mon Sep 17 00:00:00 2001
From: Christian Sachs <sachs.christian@gmail.com>
Date: Sat, 1 Mar 2025 14:50:23 +0100
Subject: [PATCH 01/10] Allow overriding module name for uv build backend

---
 crates/uv-build-backend/src/metadata.rs    | 4 ++++
 crates/uv-build-backend/src/source_dist.rs | 9 ++++++++-
 crates/uv-build-backend/src/wheel.rs       | 9 ++++++++-
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/crates/uv-build-backend/src/metadata.rs b/crates/uv-build-backend/src/metadata.rs
index 19676d6551ea7..5fc2e499b5d9a 100644
--- a/crates/uv-build-backend/src/metadata.rs
+++ b/crates/uv-build-backend/src/metadata.rs
@@ -846,6 +846,9 @@ pub(crate) struct BuildBackendSettings {
     /// using the flat layout over the src layout.
     pub(crate) module_root: PathBuf,
 
+    /// Explicitly specified module name if differing from the project name.
+    pub(crate) module_name: Option<String>,
+
     /// Glob expressions which files and directories to additionally include in the source
     /// distribution.
     ///
@@ -877,6 +880,7 @@ impl Default for BuildBackendSettings {
     fn default() -> Self {
         Self {
             module_root: PathBuf::from("src"),
+            module_name: None,
             source_include: Vec::new(),
             default_excludes: true,
             source_exclude: Vec::new(),
diff --git a/crates/uv-build-backend/src/source_dist.rs b/crates/uv-build-backend/src/source_dist.rs
index fa40840d2ed2b..375307527f67d 100644
--- a/crates/uv-build-backend/src/source_dist.rs
+++ b/crates/uv-build-backend/src/source_dist.rs
@@ -5,6 +5,7 @@ use flate2::write::GzEncoder;
 use flate2::Compression;
 use fs_err::File;
 use globset::{Glob, GlobSet};
+use std::borrow::Cow;
 use std::io;
 use std::io::{BufReader, Cursor};
 use std::path::{Path, PathBuf};
@@ -65,11 +66,17 @@ fn source_dist_matcher(
     let mut includes: Vec<String> = settings.source_include;
     // pyproject.toml is always included.
     includes.push(globset::escape("pyproject.toml"));
+
+    let module_name = settings
+        .module_name
+        .map_or(pyproject_toml.name().as_dist_info_name(), Cow::from);
+    debug!("Module name is: {:?}", module_name);
+
     // The wheel must not include any files included by the source distribution (at least until we
     // have files generated in the source dist -> wheel build step).
     let import_path = &settings
         .module_root
-        .join(pyproject_toml.name().as_dist_info_name().as_ref())
+        .join(module_name.as_ref())
         .portable_display()
         .to_string();
     includes.push(format!("{}/**", globset::escape(import_path)));
diff --git a/crates/uv-build-backend/src/wheel.rs b/crates/uv-build-backend/src/wheel.rs
index 806700665264a..64b7f7998b9ed 100644
--- a/crates/uv-build-backend/src/wheel.rs
+++ b/crates/uv-build-backend/src/wheel.rs
@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::io::{BufReader, Read, Write};
 use std::path::{Path, PathBuf};
 use std::{io, mem};
@@ -128,7 +129,13 @@ fn write_wheel(
         return Err(Error::AbsoluteModuleRoot(settings.module_root.clone()));
     }
     let strip_root = source_tree.join(settings.module_root);
-    let module_root = strip_root.join(pyproject_toml.name().as_dist_info_name().as_ref());
+
+    let module_name = settings
+        .module_name
+        .map_or(pyproject_toml.name().as_dist_info_name(), Cow::from);
+    debug!("Module name is: {:?}", module_name);
+
+    let module_root = strip_root.join(module_name.as_ref());
     if !module_root.join("__init__.py").is_file() {
         return Err(Error::MissingModule(module_root));
     }

From 593edbb14f735725b8ea52a52831d032b0451154 Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Mon, 3 Mar 2025 14:03:30 +0100
Subject: [PATCH 02/10] Add validation, docs and test.

---
 Cargo.lock                                 |   1 +
 crates/uv-build-backend/src/lib.rs         |   3 +
 crates/uv-build-backend/src/metadata.rs    |  16 ++-
 crates/uv-build-backend/src/source_dist.rs |  15 ++-
 crates/uv-build-backend/src/wheel.rs       |  22 ++--
 crates/uv-pypi-types/Cargo.toml            |   1 +
 crates/uv-pypi-types/src/identifier.rs     | 137 +++++++++++++++++++++
 crates/uv-pypi-types/src/lib.rs            |   2 +
 crates/uv/tests/it/build_backend.rs        |  84 +++++++++++++
 9 files changed, 262 insertions(+), 19 deletions(-)
 create mode 100644 crates/uv-pypi-types/src/identifier.rs

diff --git a/Cargo.lock b/Cargo.lock
index ddd116f1445f5..0f738bb09173b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5387,6 +5387,7 @@ dependencies = [
  "anyhow",
  "hashbrown 0.15.2",
  "indexmap",
+ "insta",
  "itertools 0.14.0",
  "jiff",
  "mailparse",
diff --git a/crates/uv-build-backend/src/lib.rs b/crates/uv-build-backend/src/lib.rs
index 6aa0bb86088e6..4f038256d0173 100644
--- a/crates/uv-build-backend/src/lib.rs
+++ b/crates/uv-build-backend/src/lib.rs
@@ -15,6 +15,7 @@ use thiserror::Error;
 use tracing::debug;
 use uv_fs::Simplified;
 use uv_globfilter::PortableGlobError;
+use uv_pypi_types::IdentifierParseError;
 
 #[derive(Debug, Error)]
 pub enum Error {
@@ -24,6 +25,8 @@ pub enum Error {
     Toml(#[from] toml::de::Error),
     #[error("Invalid pyproject.toml")]
     Validation(#[from] ValidationError),
+    #[error(transparent)]
+    Identifier(#[from] IdentifierParseError),
     #[error("Unsupported glob expression in: `{field}`")]
     PortableGlob {
         field: String,
diff --git a/crates/uv-build-backend/src/metadata.rs b/crates/uv-build-backend/src/metadata.rs
index 5fc2e499b5d9a..2d699faae1014 100644
--- a/crates/uv-build-backend/src/metadata.rs
+++ b/crates/uv-build-backend/src/metadata.rs
@@ -17,7 +17,7 @@ use uv_pep440::{Version, VersionSpecifiers};
 use uv_pep508::{
     ExtraOperator, MarkerExpression, MarkerTree, MarkerValueExtra, Requirement, VersionOrUrl,
 };
-use uv_pypi_types::{Metadata23, VerbatimParsedUrl};
+use uv_pypi_types::{Identifier, Metadata23, VerbatimParsedUrl};
 
 use crate::serde_verbatim::SerdeVerbatim;
 use crate::Error;
@@ -803,7 +803,7 @@ pub(crate) struct ToolUv {
 /// When building the source distribution, the following files and directories are included:
 /// * `pyproject.toml`
 /// * The module under `tool.uv.build-backend.module-root`, by default
-///   `src/<project_name_with_underscores>/**`.
+///   `src/<module-name or project_name_with_underscores>/**`.
 /// * `project.license-files` and `project.readme`.
 /// * All directories under `tool.uv.build-backend.data`.
 /// * All patterns from `tool.uv.build-backend.source-include`.
@@ -812,7 +812,7 @@ pub(crate) struct ToolUv {
 ///
 /// When building the wheel, the following files and directories are included:
 /// * The module under `tool.uv.build-backend.module-root`, by default
-///   `src/<project_name_with_underscores>/**`.
+///   `src/<module-name or project_name_with_underscores>/**`.
 /// * `project.license-files` and `project.readme`, as part of the project metadata.
 /// * Each directory under `tool.uv.build-backend.data`, as data directories.
 ///
@@ -846,8 +846,14 @@ pub(crate) struct BuildBackendSettings {
     /// using the flat layout over the src layout.
     pub(crate) module_root: PathBuf,
 
-    /// Explicitly specified module name if differing from the project name.
-    pub(crate) module_name: Option<String>,
+    /// The name of the module directory inside `module-root`.
+    ///
+    /// The default module name is the package name with dots and dashes replaced by underscores.
+    ///
+    /// Note that using this option runs the risk of creating two packages with different names but
+    /// the same module names. Installing such packages together leads to undefined behavior, often
+    /// with corrupted files or directory trees.
+    pub(crate) module_name: Option<Identifier>,
 
     /// Glob expressions which files and directories to additionally include in the source
     /// distribution.
diff --git a/crates/uv-build-backend/src/source_dist.rs b/crates/uv-build-backend/src/source_dist.rs
index 375307527f67d..991d8ec67d794 100644
--- a/crates/uv-build-backend/src/source_dist.rs
+++ b/crates/uv-build-backend/src/source_dist.rs
@@ -5,15 +5,16 @@ use flate2::write::GzEncoder;
 use flate2::Compression;
 use fs_err::File;
 use globset::{Glob, GlobSet};
-use std::borrow::Cow;
 use std::io;
 use std::io::{BufReader, Cursor};
 use std::path::{Path, PathBuf};
+use std::str::FromStr;
 use tar::{EntryType, Header};
 use tracing::{debug, trace};
 use uv_distribution_filename::{SourceDistExtension, SourceDistFilename};
 use uv_fs::Simplified;
 use uv_globfilter::{parse_portable_glob, GlobDirFilter};
+use uv_pypi_types::Identifier;
 use uv_warnings::warn_user_once;
 use walkdir::WalkDir;
 
@@ -67,10 +68,14 @@ fn source_dist_matcher(
     // pyproject.toml is always included.
     includes.push(globset::escape("pyproject.toml"));
 
-    let module_name = settings
-        .module_name
-        .map_or(pyproject_toml.name().as_dist_info_name(), Cow::from);
-    debug!("Module name is: {:?}", module_name);
+    let module_name = if let Some(module_name) = settings.module_name {
+        module_name
+    } else {
+        // Should never happen, the rules for package names (in dist-info formatting) are stricter
+        // than those for identifiers
+        Identifier::from_str(pyproject_toml.name().as_dist_info_name().as_ref())?
+    };
+    debug!("Module name: `{:?}`", module_name);
 
     // The wheel must not include any files included by the source distribution (at least until we
     // have files generated in the source dist -> wheel build step).
diff --git a/crates/uv-build-backend/src/wheel.rs b/crates/uv-build-backend/src/wheel.rs
index 64b7f7998b9ed..dc3ab0491ccf7 100644
--- a/crates/uv-build-backend/src/wheel.rs
+++ b/crates/uv-build-backend/src/wheel.rs
@@ -1,12 +1,11 @@
-use std::borrow::Cow;
-use std::io::{BufReader, Read, Write};
-use std::path::{Path, PathBuf};
-use std::{io, mem};
-
 use fs_err::File;
 use globset::{GlobSet, GlobSetBuilder};
 use itertools::Itertools;
 use sha2::{Digest, Sha256};
+use std::io::{BufReader, Read, Write};
+use std::path::{Path, PathBuf};
+use std::str::FromStr;
+use std::{io, mem};
 use tracing::{debug, trace};
 use walkdir::WalkDir;
 use zip::{CompressionMethod, ZipWriter};
@@ -15,6 +14,7 @@ use uv_distribution_filename::WheelFilename;
 use uv_fs::Simplified;
 use uv_globfilter::{parse_portable_glob, GlobDirFilter};
 use uv_platform_tags::{AbiTag, LanguageTag, PlatformTag};
+use uv_pypi_types::Identifier;
 use uv_warnings::warn_user_once;
 
 use crate::metadata::{BuildBackendSettings, DEFAULT_EXCLUDES};
@@ -130,10 +130,14 @@ fn write_wheel(
     }
     let strip_root = source_tree.join(settings.module_root);
 
-    let module_name = settings
-        .module_name
-        .map_or(pyproject_toml.name().as_dist_info_name(), Cow::from);
-    debug!("Module name is: {:?}", module_name);
+    let module_name = if let Some(module_name) = settings.module_name {
+        module_name
+    } else {
+        // Should never happen, the rules for package names (in dist-info formatting) are stricter
+        // than those for identifiers
+        Identifier::from_str(pyproject_toml.name().as_dist_info_name().as_ref())?
+    };
+    debug!("Module name: `{:?}`", module_name);
 
     let module_root = strip_root.join(module_name.as_ref());
     if !module_root.join("__init__.py").is_file() {
diff --git a/crates/uv-pypi-types/Cargo.toml b/crates/uv-pypi-types/Cargo.toml
index fe97710d767bc..190f5c433d267 100644
--- a/crates/uv-pypi-types/Cargo.toml
+++ b/crates/uv-pypi-types/Cargo.toml
@@ -42,6 +42,7 @@ url = { workspace = true }
 
 [dev-dependencies]
 anyhow = { workspace = true }
+insta = { version = "1.40.0"}
 
 [features]
 schemars = ["dep:schemars", "uv-normalize/schemars"]
diff --git a/crates/uv-pypi-types/src/identifier.rs b/crates/uv-pypi-types/src/identifier.rs
new file mode 100644
index 0000000000000..3652e52a7bd1b
--- /dev/null
+++ b/crates/uv-pypi-types/src/identifier.rs
@@ -0,0 +1,137 @@
+use std::fmt::Display;
+use std::str::FromStr;
+use thiserror::Error;
+
+/// Simplified Python identifier.
+///
+/// We don't match Python's identifier rules
+/// (<https://docs.python.org/3.13/reference/lexical_analysis.html#identifiers>) exactly
+/// (we just use Rust's `is_alphabetic`) and we don't convert to NFKC, but it's good enough
+/// for our validation purposes.
+#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Identifier(String);
+
+#[derive(Debug, Clone, Error)]
+pub enum IdentifierParseError {
+    #[error("An identifier must not be empty")]
+    Empty,
+    #[error(
+        "Invalid first character `{first}` at for `{identifier}`, expected an underscore or an alphabetic character"
+    )]
+    InvalidFirstChar { first: char, identifier: String },
+    #[error(
+        "Invalid character `{invalid_char}` at position {pos} for `{identifier}`, expected an underscore or an alphanumeric character"
+    )]
+    InvalidChar {
+        pos: usize,
+        invalid_char: char,
+        identifier: String,
+    },
+}
+
+impl Identifier {
+    pub fn new(identifier: String) -> Result<Self, IdentifierParseError> {
+        let mut chars = identifier.chars().enumerate();
+        let (_, first_char) = chars.next().ok_or(IdentifierParseError::Empty)?;
+        if first_char != '_' && !first_char.is_alphabetic() {
+            return Err(IdentifierParseError::InvalidFirstChar {
+                first: first_char,
+                identifier,
+            });
+        }
+
+        for (pos, current_char) in chars {
+            if current_char != '_' && !current_char.is_alphanumeric() {
+                return Err(IdentifierParseError::InvalidChar {
+                    // Make the position 1-indexed
+                    pos: pos + 1,
+                    invalid_char: current_char,
+                    identifier,
+                });
+            }
+        }
+
+        Ok(Self(identifier))
+    }
+}
+
+impl FromStr for Identifier {
+    type Err = IdentifierParseError;
+
+    fn from_str(identifier: &str) -> Result<Self, Self::Err> {
+        Self::new(identifier.to_string())
+    }
+}
+
+impl Display for Identifier {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl AsRef<str> for Identifier {
+    fn as_ref(&self) -> &str {
+        &self.0
+    }
+}
+
+impl<'de> serde::de::Deserialize<'de> for Identifier {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::de::Deserializer<'de>,
+    {
+        let s = String::deserialize(deserializer)?;
+        Identifier::from_str(&s).map_err(serde::de::Error::custom)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use insta::assert_snapshot;
+
+    #[test]
+    fn valid() {
+        let valid_ids = vec![
+            "abc",
+            "_abc",
+            "a_bc",
+            "a123",
+            "snake_case",
+            "camelCase",
+            "PascalCase",
+            // A single character is valid
+            "_",
+            "a",
+            // Unicode
+            "α",
+            "férrîs",
+            "안녕하세요",
+        ];
+
+        for valid_id in valid_ids {
+            assert!(Identifier::from_str(valid_id).is_ok(), "{}", valid_id);
+        }
+    }
+
+    #[test]
+    fn empty() {
+        assert_snapshot!(Identifier::from_str("").unwrap_err(), @"An identifier must not be empty");
+    }
+
+    #[test]
+    fn invalid_first_char() {
+        assert_snapshot!(Identifier::from_str("1foo").unwrap_err(), @"Invalid first character `1` at for `1foo`, expected an underscore or an alphabetic character");
+        assert_snapshot!(Identifier::from_str("$foo").unwrap_err(), @"Invalid first character `$` at for `$foo`, expected an underscore or an alphabetic character");
+        assert_snapshot!(Identifier::from_str(".foo").unwrap_err(), @"Invalid first character `.` at for `.foo`, expected an underscore or an alphabetic character");
+    }
+
+    #[test]
+    fn invalid_char() {
+        // A dot in module names equals a path separator, which is a separate problem.
+        assert_snapshot!(Identifier::from_str("foo.bar").unwrap_err(), @"Invalid character `.` at position 4 for `foo.bar`, expected an underscore or an alphanumeric character");
+        assert_snapshot!(Identifier::from_str("foo-bar").unwrap_err(), @"Invalid character `-` at position 4 for `foo-bar`, expected an underscore or an alphanumeric character");
+        assert_snapshot!(Identifier::from_str("foo_bar$").unwrap_err(), @"Invalid character `$` at position 8 for `foo_bar$`, expected an underscore or an alphanumeric character");
+        assert_snapshot!(Identifier::from_str("foo🦀bar").unwrap_err(), @"Invalid character `🦀` at position 4 for `foo🦀bar`, expected an underscore or an alphanumeric character");
+    }
+}
diff --git a/crates/uv-pypi-types/src/lib.rs b/crates/uv-pypi-types/src/lib.rs
index a3b2b6e05c26d..a5c9ec8a4b564 100644
--- a/crates/uv-pypi-types/src/lib.rs
+++ b/crates/uv-pypi-types/src/lib.rs
@@ -2,6 +2,7 @@ pub use base_url::*;
 pub use conflicts::*;
 pub use dependency_groups::*;
 pub use direct_url::*;
+pub use identifier::*;
 pub use lenient_requirement::*;
 pub use marker_environment::*;
 pub use metadata::*;
@@ -15,6 +16,7 @@ mod base_url;
 mod conflicts;
 mod dependency_groups;
 mod direct_url;
+mod identifier;
 mod lenient_requirement;
 mod marker_environment;
 mod metadata;
diff --git a/crates/uv/tests/it/build_backend.rs b/crates/uv/tests/it/build_backend.rs
index 7c9320532d08c..29fa944f516ca 100644
--- a/crates/uv/tests/it/build_backend.rs
+++ b/crates/uv/tests/it/build_backend.rs
@@ -1,6 +1,7 @@
 use crate::common::{uv_snapshot, venv_bin_path, TestContext};
 use anyhow::Result;
 use assert_cmd::assert::OutputAssertExt;
+use assert_fs::fixture::{FileWriteStr, PathChild};
 use flate2::bufread::GzDecoder;
 use fs_err::File;
 use indoc::indoc;
@@ -278,3 +279,86 @@ fn preserve_executable_bit() -> Result<()> {
 
     Ok(())
 }
+
+/// Test `tool.uv.build-backend.module-name`.
+#[test]
+fn rename_module() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let temp_dir = TempDir::new()?;
+
+    context
+        .temp_dir
+        .child("pyproject.toml")
+        .write_str(indoc! {r#"
+        [project]
+        name = "foo"
+        version = "1.0.0"
+
+        [tool.uv.build-backend]
+        module-name = "bar"
+
+        [build-system]
+        requires = ["uv>=0.5,<0.7"]
+        build-backend = "uv"
+    "#})?;
+
+    context
+        .temp_dir
+        .child("src/foo/__init__.py")
+        .write_str(r#"print("Hi from foo")"#)?;
+    context
+        .temp_dir
+        .child("src/bar/__init__.py")
+        .write_str(r#"print("Hi from bar")"#)?;
+
+    uv_snapshot!(context
+        .build_backend()
+        .arg("build-wheel")
+        .arg(temp_dir.path())
+        .env("UV_PREVIEW", "1"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    foo-1.0.0-py3-none-any.whl
+
+    ----- stderr -----
+    "###);
+
+    context
+        .pip_install()
+        .arg(temp_dir.path().join("foo-1.0.0-py3-none-any.whl"))
+        .assert()
+        .success();
+
+    // Importing the renamed module succeeds
+    uv_snapshot!(Command::new(context.interpreter())
+        .arg("-c")
+        .arg("import bar")
+        // Python on windows
+        .env(EnvVars::PYTHONUTF8, "1"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Hi from bar
+
+    ----- stderr -----
+    "###);
+
+    // Importing the package name fails
+    uv_snapshot!(Command::new(context.interpreter())
+        .arg("-c")
+        .arg("import foo")
+        // Python on windows
+        .env(EnvVars::PYTHONUTF8, "1"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+    Traceback (most recent call last):
+      File "<string>", line 1, in <module>
+    ModuleNotFoundError: No module named 'foo'
+    "###);
+
+    Ok(())
+}

From 24b8c8a16381fe150e293c522525d8f87c3ab9fc Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Thu, 6 Mar 2025 09:39:08 +0100
Subject: [PATCH 03/10] Review

---
 Cargo.lock                                 | 20 ++++-----
 crates/uv-build-backend/src/metadata.rs    |  4 +-
 crates/uv-build-backend/src/source_dist.rs |  2 +-
 crates/uv-build-backend/src/wheel.rs       |  2 +-
 crates/uv-pypi-types/src/identifier.rs     | 49 ++++++++++++++++------
 crates/uv/tests/it/build_backend.rs        | 10 ++++-
 6 files changed, 58 insertions(+), 29 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 0f738bb09173b..2293886f3826e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -688,7 +688,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "117725a109d387c937a1533ce01b450cbde6b88abceea8473c4d7a85853cda3c"
 dependencies = [
  "lazy_static",
- "windows-sys 0.59.0",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
@@ -1042,7 +1042,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
 dependencies = [
  "libc",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -1841,9 +1841,9 @@ checksum = "b248f5224d1d606005e02c97f5aa4e88eeb230488bcc03bc9ca4d7991399f2b5"
 
 [[package]]
 name = "insta"
-version = "1.42.2"
+version = "1.42.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "50259abbaa67d11d2bcafc7ba1d094ed7a0c70e3ce893f0d0997f73558cb3084"
+checksum = "71c1b125e30d93896b365e156c33dadfffab45ee8400afcbba4752f59de08a86"
 dependencies = [
  "console",
  "linked-hash-map",
@@ -1882,7 +1882,7 @@ checksum = "e19b23d53f35ce9f56aebc7d1bb4e6ac1e9c0db7ac85c8d1760c04379edced37"
 dependencies = [
  "hermit-abi 0.4.0",
  "libc",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -1941,7 +1941,7 @@ dependencies = [
  "portable-atomic",
  "portable-atomic-util",
  "serde",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -2806,7 +2806,7 @@ dependencies = [
  "once_cell",
  "socket2",
  "tracing",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -3236,7 +3236,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -3817,7 +3817,7 @@ dependencies = [
  "getrandom 0.3.1",
  "once_cell",
  "rustix",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -6046,7 +6046,7 @@ version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
 dependencies = [
- "windows-sys 0.59.0",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
diff --git a/crates/uv-build-backend/src/metadata.rs b/crates/uv-build-backend/src/metadata.rs
index 2d699faae1014..50de430af6e17 100644
--- a/crates/uv-build-backend/src/metadata.rs
+++ b/crates/uv-build-backend/src/metadata.rs
@@ -851,8 +851,8 @@ pub(crate) struct BuildBackendSettings {
     /// The default module name is the package name with dots and dashes replaced by underscores.
     ///
     /// Note that using this option runs the risk of creating two packages with different names but
-    /// the same module names. Installing such packages together leads to undefined behavior, often
-    /// with corrupted files or directory trees.
+    /// the same module names. Installing such packages together leads to unspecified behavior,
+    /// often with corrupted files or directory trees.
     pub(crate) module_name: Option<Identifier>,
 
     /// Glob expressions which files and directories to additionally include in the source
diff --git a/crates/uv-build-backend/src/source_dist.rs b/crates/uv-build-backend/src/source_dist.rs
index 991d8ec67d794..3449ee4e02b98 100644
--- a/crates/uv-build-backend/src/source_dist.rs
+++ b/crates/uv-build-backend/src/source_dist.rs
@@ -71,7 +71,7 @@ fn source_dist_matcher(
     let module_name = if let Some(module_name) = settings.module_name {
         module_name
     } else {
-        // Should never happen, the rules for package names (in dist-info formatting) are stricter
+        // Should never error, the rules for package names (in dist-info formatting) are stricter
         // than those for identifiers
         Identifier::from_str(pyproject_toml.name().as_dist_info_name().as_ref())?
     };
diff --git a/crates/uv-build-backend/src/wheel.rs b/crates/uv-build-backend/src/wheel.rs
index dc3ab0491ccf7..f14cdc5267f75 100644
--- a/crates/uv-build-backend/src/wheel.rs
+++ b/crates/uv-build-backend/src/wheel.rs
@@ -133,7 +133,7 @@ fn write_wheel(
     let module_name = if let Some(module_name) = settings.module_name {
         module_name
     } else {
-        // Should never happen, the rules for package names (in dist-info formatting) are stricter
+        // Should never error, the rules for package names (in dist-info formatting) are stricter
         // than those for identifiers
         Identifier::from_str(pyproject_toml.name().as_dist_info_name().as_ref())?
     };
diff --git a/crates/uv-pypi-types/src/identifier.rs b/crates/uv-pypi-types/src/identifier.rs
index 3652e52a7bd1b..9b9bad8c5a4b6 100644
--- a/crates/uv-pypi-types/src/identifier.rs
+++ b/crates/uv-pypi-types/src/identifier.rs
@@ -9,28 +9,30 @@ use thiserror::Error;
 /// (we just use Rust's `is_alphabetic`) and we don't convert to NFKC, but it's good enough
 /// for our validation purposes.
 #[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
-pub struct Identifier(String);
+pub struct Identifier(Box<str>);
 
 #[derive(Debug, Clone, Error)]
 pub enum IdentifierParseError {
     #[error("An identifier must not be empty")]
     Empty,
     #[error(
-        "Invalid first character `{first}` at for `{identifier}`, expected an underscore or an alphabetic character"
+        "Invalid first character `{first}` for identifier `{identifier}`, expected an underscore or an alphabetic character"
     )]
-    InvalidFirstChar { first: char, identifier: String },
+    InvalidFirstChar { first: char, identifier: Box<str> },
     #[error(
-        "Invalid character `{invalid_char}` at position {pos} for `{identifier}`, expected an underscore or an alphanumeric character"
+        "Invalid character `{invalid_char}` at position {pos} for identifier `{identifier}`, \
+        expected an underscore or an alphanumeric character"
     )]
     InvalidChar {
         pos: usize,
         invalid_char: char,
-        identifier: String,
+        identifier: Box<str>,
     },
 }
 
 impl Identifier {
-    pub fn new(identifier: String) -> Result<Self, IdentifierParseError> {
+    pub fn new(identifier: impl Into<Box<str>>) -> Result<Self, IdentifierParseError> {
+        let identifier = identifier.into();
         let mut chars = identifier.chars().enumerate();
         let (_, first_char) = chars.next().ok_or(IdentifierParseError::Empty)?;
         if first_char != '_' && !first_char.is_alphabetic() {
@@ -121,17 +123,38 @@ mod tests {
 
     #[test]
     fn invalid_first_char() {
-        assert_snapshot!(Identifier::from_str("1foo").unwrap_err(), @"Invalid first character `1` at for `1foo`, expected an underscore or an alphabetic character");
-        assert_snapshot!(Identifier::from_str("$foo").unwrap_err(), @"Invalid first character `$` at for `$foo`, expected an underscore or an alphabetic character");
-        assert_snapshot!(Identifier::from_str(".foo").unwrap_err(), @"Invalid first character `.` at for `.foo`, expected an underscore or an alphabetic character");
+        assert_snapshot!(
+            Identifier::from_str("1foo").unwrap_err(),
+            @"Invalid first character `1` at for `1foo`, expected an underscore or an alphabetic character"
+        );
+        assert_snapshot!(
+            Identifier::from_str("$foo").unwrap_err(),
+            @"Invalid first character `$` at for `$foo`, expected an underscore or an alphabetic character"
+        );
+        assert_snapshot!(
+            Identifier::from_str(".foo").unwrap_err(),
+            @"Invalid first character `.` at for `.foo`, expected an underscore or an alphabetic character"
+        );
     }
 
     #[test]
     fn invalid_char() {
         // A dot in module names equals a path separator, which is a separate problem.
-        assert_snapshot!(Identifier::from_str("foo.bar").unwrap_err(), @"Invalid character `.` at position 4 for `foo.bar`, expected an underscore or an alphanumeric character");
-        assert_snapshot!(Identifier::from_str("foo-bar").unwrap_err(), @"Invalid character `-` at position 4 for `foo-bar`, expected an underscore or an alphanumeric character");
-        assert_snapshot!(Identifier::from_str("foo_bar$").unwrap_err(), @"Invalid character `$` at position 8 for `foo_bar$`, expected an underscore or an alphanumeric character");
-        assert_snapshot!(Identifier::from_str("foo🦀bar").unwrap_err(), @"Invalid character `🦀` at position 4 for `foo🦀bar`, expected an underscore or an alphanumeric character");
+        assert_snapshot!(
+            Identifier::from_str("foo.bar").unwrap_err(),
+            @"Invalid character `.` at position 4 for `foo.bar`, expected an underscore or an alphanumeric character"
+        );
+        assert_snapshot!(
+            Identifier::from_str("foo-bar").unwrap_err(),
+            @"Invalid character `-` at position 4 for `foo-bar`, expected an underscore or an alphanumeric character"
+        );
+        assert_snapshot!(
+            Identifier::from_str("foo_bar$").unwrap_err(),
+            @"Invalid character `$` at position 8 for `foo_bar$`, expected an underscore or an alphanumeric character"
+        );
+        assert_snapshot!(
+            Identifier::from_str("foo🦀bar").unwrap_err(),
+            @"Invalid character `🦀` at position 4 for `foo🦀bar`, expected an underscore or an alphanumeric character"
+        );
     }
 }
diff --git a/crates/uv/tests/it/build_backend.rs b/crates/uv/tests/it/build_backend.rs
index 29fa944f516ca..05272db78231f 100644
--- a/crates/uv/tests/it/build_backend.rs
+++ b/crates/uv/tests/it/build_backend.rs
@@ -281,6 +281,9 @@ fn preserve_executable_bit() -> Result<()> {
 }
 
 /// Test `tool.uv.build-backend.module-name`.
+///
+/// We include only the module specified by `module-name`, ignoring the project name and all other
+/// potential modules.
 #[test]
 fn rename_module() -> Result<()> {
     let context = TestContext::new("3.12");
@@ -302,10 +305,13 @@ fn rename_module() -> Result<()> {
         build-backend = "uv"
     "#})?;
 
+    // This is the module we would usually include, but due to the renaming by `module-name` must
+    // ignore.
     context
         .temp_dir
         .child("src/foo/__init__.py")
         .write_str(r#"print("Hi from foo")"#)?;
+    // This module would be ignored from just `project.name`, but is selected due to the renaming.
     context
         .temp_dir
         .child("src/bar/__init__.py")
@@ -330,7 +336,7 @@ fn rename_module() -> Result<()> {
         .assert()
         .success();
 
-    // Importing the renamed module succeeds
+    // Importing the module with the `module-name` name succeeds.
     uv_snapshot!(Command::new(context.interpreter())
         .arg("-c")
         .arg("import bar")
@@ -344,7 +350,7 @@ fn rename_module() -> Result<()> {
     ----- stderr -----
     "###);
 
-    // Importing the package name fails
+    // Importing the package name fails, it was overridden by `module-name`.
     uv_snapshot!(Command::new(context.interpreter())
         .arg("-c")
         .arg("import foo")

From f533804991de68ef592e001882d04bfc0aa49efe Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Thu, 6 Mar 2025 09:42:20 +0100
Subject: [PATCH 04/10] Reset Cargo.lock

---
 Cargo.lock | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 2293886f3826e..ddd116f1445f5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -688,7 +688,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "117725a109d387c937a1533ce01b450cbde6b88abceea8473c4d7a85853cda3c"
 dependencies = [
  "lazy_static",
- "windows-sys 0.48.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -1042,7 +1042,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
 dependencies = [
  "libc",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -1841,9 +1841,9 @@ checksum = "b248f5224d1d606005e02c97f5aa4e88eeb230488bcc03bc9ca4d7991399f2b5"
 
 [[package]]
 name = "insta"
-version = "1.42.1"
+version = "1.42.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "71c1b125e30d93896b365e156c33dadfffab45ee8400afcbba4752f59de08a86"
+checksum = "50259abbaa67d11d2bcafc7ba1d094ed7a0c70e3ce893f0d0997f73558cb3084"
 dependencies = [
  "console",
  "linked-hash-map",
@@ -1882,7 +1882,7 @@ checksum = "e19b23d53f35ce9f56aebc7d1bb4e6ac1e9c0db7ac85c8d1760c04379edced37"
 dependencies = [
  "hermit-abi 0.4.0",
  "libc",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -1941,7 +1941,7 @@ dependencies = [
  "portable-atomic",
  "portable-atomic-util",
  "serde",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -2806,7 +2806,7 @@ dependencies = [
  "once_cell",
  "socket2",
  "tracing",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -3236,7 +3236,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -3817,7 +3817,7 @@ dependencies = [
  "getrandom 0.3.1",
  "once_cell",
  "rustix",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -5387,7 +5387,6 @@ dependencies = [
  "anyhow",
  "hashbrown 0.15.2",
  "indexmap",
- "insta",
  "itertools 0.14.0",
  "jiff",
  "mailparse",
@@ -6046,7 +6045,7 @@ version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
 dependencies = [
- "windows-sys 0.48.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]

From 4cebea89adb3b083fb6fc51f4bd670d785f732ac Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Thu, 6 Mar 2025 17:41:37 +0100
Subject: [PATCH 05/10] Update lockfile

---
 Cargo.lock | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Cargo.lock b/Cargo.lock
index ddd116f1445f5..0f738bb09173b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5387,6 +5387,7 @@ dependencies = [
  "anyhow",
  "hashbrown 0.15.2",
  "indexmap",
+ "insta",
  "itertools 0.14.0",
  "jiff",
  "mailparse",

From 98edd36bbc473dae3a4967df46c44b6d50cdb778 Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Thu, 6 Mar 2025 17:46:14 +0100
Subject: [PATCH 06/10] Update snapshots

---
 crates/uv-pypi-types/src/identifier.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/uv-pypi-types/src/identifier.rs b/crates/uv-pypi-types/src/identifier.rs
index 9b9bad8c5a4b6..0ff550f792e93 100644
--- a/crates/uv-pypi-types/src/identifier.rs
+++ b/crates/uv-pypi-types/src/identifier.rs
@@ -125,7 +125,7 @@ mod tests {
     fn invalid_first_char() {
         assert_snapshot!(
             Identifier::from_str("1foo").unwrap_err(),
-            @"Invalid first character `1` at for `1foo`, expected an underscore or an alphabetic character"
+            @"Invalid first character `1` for identifier `1foo`, expected an underscore or an alphabetic character"
         );
         assert_snapshot!(
             Identifier::from_str("$foo").unwrap_err(),
@@ -142,7 +142,7 @@ mod tests {
         // A dot in module names equals a path separator, which is a separate problem.
         assert_snapshot!(
             Identifier::from_str("foo.bar").unwrap_err(),
-            @"Invalid character `.` at position 4 for `foo.bar`, expected an underscore or an alphanumeric character"
+            @"Invalid character `.` at position 4 for identifier `foo.bar`, expected an underscore or an alphanumeric character"
         );
         assert_snapshot!(
             Identifier::from_str("foo-bar").unwrap_err(),

From 4efa388e7aa860ee1f4f1e40e5479627c462f07c Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Fri, 7 Mar 2025 14:26:04 +0100
Subject: [PATCH 07/10] Update snapshots

---
 crates/uv-pypi-types/src/identifier.rs | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/crates/uv-pypi-types/src/identifier.rs b/crates/uv-pypi-types/src/identifier.rs
index 0ff550f792e93..42bda8175a7da 100644
--- a/crates/uv-pypi-types/src/identifier.rs
+++ b/crates/uv-pypi-types/src/identifier.rs
@@ -129,11 +129,11 @@ mod tests {
         );
         assert_snapshot!(
             Identifier::from_str("$foo").unwrap_err(),
-            @"Invalid first character `$` at for `$foo`, expected an underscore or an alphabetic character"
+            @"Invalid first character `$` for identifier `$foo`, expected an underscore or an alphabetic character"
         );
         assert_snapshot!(
             Identifier::from_str(".foo").unwrap_err(),
-            @"Invalid first character `.` at for `.foo`, expected an underscore or an alphabetic character"
+            @"Invalid first character `.` for identifier `.foo`, expected an underscore or an alphabetic character"
         );
     }
 
@@ -146,15 +146,15 @@ mod tests {
         );
         assert_snapshot!(
             Identifier::from_str("foo-bar").unwrap_err(),
-            @"Invalid character `-` at position 4 for `foo-bar`, expected an underscore or an alphanumeric character"
+            @"Invalid character `-` at position 4 for identifier `foo-bar`, expected an underscore or an alphanumeric character"
         );
         assert_snapshot!(
             Identifier::from_str("foo_bar$").unwrap_err(),
-            @"Invalid character `$` at position 8 for `foo_bar$`, expected an underscore or an alphanumeric character"
+            @"Invalid character `$` at position 8 for identifier `foo_bar$`, expected an underscore or an alphanumeric character"
         );
         assert_snapshot!(
             Identifier::from_str("foo🦀bar").unwrap_err(),
-            @"Invalid character `🦀` at position 4 for `foo🦀bar`, expected an underscore or an alphanumeric character"
+            @"Invalid character `🦀` at position 4 for identifier `foo🦀bar`, expected an underscore or an alphanumeric character"
         );
     }
 }

From ee96f0b9c8355b50c8c4b831a03201943216575f Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Fri, 7 Mar 2025 14:37:46 +0100
Subject: [PATCH 08/10] Rebase onto main

---
 crates/uv/tests/it/build_backend.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/uv/tests/it/build_backend.rs b/crates/uv/tests/it/build_backend.rs
index 05272db78231f..731bcdfaf8f93 100644
--- a/crates/uv/tests/it/build_backend.rs
+++ b/crates/uv/tests/it/build_backend.rs
@@ -301,8 +301,8 @@ fn rename_module() -> Result<()> {
         module-name = "bar"
 
         [build-system]
-        requires = ["uv>=0.5,<0.7"]
-        build-backend = "uv"
+        requires = ["uv_build>=0.5,<0.7"]
+        build-backend = "uv_build"
     "#})?;
 
     // This is the module we would usually include, but due to the renaming by `module-name` must

From 7bdf701fac7044243fa9c7e2a0826da5f41e613c Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Fri, 7 Mar 2025 14:52:28 +0100
Subject: [PATCH 09/10] serde is not optional in uv-pypi-types

---
 crates/uv-pypi-types/Cargo.toml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/uv-pypi-types/Cargo.toml b/crates/uv-pypi-types/Cargo.toml
index 190f5c433d267..db515b86a1e52 100644
--- a/crates/uv-pypi-types/Cargo.toml
+++ b/crates/uv-pypi-types/Cargo.toml
@@ -32,7 +32,7 @@ mailparse = { workspace = true }
 regex = { workspace = true }
 rkyv = { workspace = true }
 schemars = { workspace = true, optional = true }
-serde = { workspace = true, optional = true }
+serde = { workspace = true }
 serde-untagged = { workspace = true }
 thiserror = { workspace = true }
 toml = { workspace = true }
@@ -42,7 +42,7 @@ url = { workspace = true }
 
 [dev-dependencies]
 anyhow = { workspace = true }
-insta = { version = "1.40.0"}
+insta = { version = "1.40.0" }
 
 [features]
 schemars = ["dep:schemars", "uv-normalize/schemars"]

From 2ca4cbf2ed2cce496be7ea51ff34acd919151941 Mon Sep 17 00:00:00 2001
From: konstin <konstin@mailbox.org>
Date: Fri, 7 Mar 2025 14:56:52 +0100
Subject: [PATCH 10/10] serde is not optional in uv-pypi-types

---
 crates/uv-workspace/Cargo.toml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/crates/uv-workspace/Cargo.toml b/crates/uv-workspace/Cargo.toml
index 43f4a53a941a1..0ba386accff81 100644
--- a/crates/uv-workspace/Cargo.toml
+++ b/crates/uv-workspace/Cargo.toml
@@ -25,7 +25,7 @@ uv-normalize = { workspace = true }
 uv-options-metadata = { workspace = true }
 uv-pep440 = { workspace = true }
 uv-pep508 = { workspace = true }
-uv-pypi-types = { workspace = true, features = ["serde"] }
+uv-pypi-types = { workspace = true }
 uv-static = { workspace = true }
 uv-warnings = { workspace = true }
 
@@ -38,8 +38,8 @@ schemars = { workspace = true, optional = true }
 serde = { workspace = true, features = ["derive"] }
 thiserror = { workspace = true }
 tokio = { workspace = true }
-toml =  { workspace = true }
-toml_edit =  { workspace = true }
+toml = { workspace = true }
+toml_edit = { workspace = true }
 tracing = { workspace = true }
 url = { workspace = true }