Show dedicated error for trailing ; on URL and path requirements (#8835)

## Summary

I think we lost this error in a prior refactor. I've added an end-to-end
test too.

crates/uv-pep508/src/lib.rs

@@ -731,6 +731,19 @@ fn parse_url<T: Pep508Url>(
         });
     }
 
+    for c in [';', '#'] {
+        if url.ends_with(c) {
+            return Err(Pep508Error {
+                message: Pep508ErrorSource::String(format!(
+                    "Missing space before '{c}', the end of the URL is ambiguous"
+                )),
+                start: start + len - 1,
+                len: 1,
+                input: cursor.to_string(),
+            });
+        }
+    }
+
     let url = T::parse_url(url, working_dir).map_err(|err| Pep508Error {
         message: Pep508ErrorSource::UrlError(err),
         start,
@@ -927,8 +940,6 @@ fn parse_pep508_requirement<T: Pep508Url>(
         }
     };
 
-    let requirement_end = cursor.pos();
-
     // If the requirement consists solely of a package name, and that name appears to be an archive,
     // treat it as a URL requirement, for consistency and security. (E.g., `requests-2.26.0.tar.gz`
     // is a valid Python package name, but we should treat it as a reference to a file.)
@@ -960,23 +971,6 @@ fn parse_pep508_requirement<T: Pep508Url>(
     // wsp*
     cursor.eat_whitespace();
     if let Some((pos, char)) = cursor.next() {
-        if marker.is_none() {
-            if let Some(VersionOrUrl::Url(url)) = requirement_kind {
-                let url = url.to_string();
-                for c in [';', '#'] {
-                    if url.ends_with(c) {
-                        return Err(Pep508Error {
-                            message: Pep508ErrorSource::String(format!(
-                                "Missing space before '{c}', the end of the URL is ambiguous"
-                            )),
-                            start: requirement_end - c.len_utf8(),
-                            len: c.len_utf8(),
-                            input: cursor.to_string(),
-                        });
-                    }
-                }
-            }
-        }
         let message = if marker.is_none() {
             format!(r#"Expected end of input or `;`, found `{char}`"#)
         } else {

crates/uv-pep508/src/tests.rs

@@ -557,6 +557,30 @@ fn error_no_space_after_url() {
     );
 }
 
+#[test]
+fn error_no_space_after_file_url() {
+    assert_snapshot!(
+        parse_pep508_err(r"name @ file:///test.whl; extra == 'example'"),
+        @r###"
+    Missing space before ';', the end of the URL is ambiguous
+    name @ file:///test.whl; extra == 'example'
+                           ^
+    "###
+    );
+}
+
+#[test]
+fn error_no_space_after_file_path() {
+    assert_snapshot!(
+        parse_pep508_err(r"name @ ./test.whl; extra == 'example'"),
+        @r###"
+    Missing space before ';', the end of the URL is ambiguous
+    name @ ./test.whl; extra == 'example'
+                     ^
+    "###
+    );
+}
+
 #[test]
 fn error_name_at_nothing() {
     assert_snapshot!(

crates/uv-pep508/src/unnamed.rs

@@ -160,7 +160,6 @@ fn parse_unnamed_requirement<Url: UnnamedRequirementUrl>(
 
     // Parse the URL itself, along with any extras.
     let (url, extras) = parse_unnamed_url::<Url>(cursor, working_dir)?;
-    let requirement_end = cursor.pos();
 
     // wsp*
     cursor.eat_whitespace();
@@ -175,22 +174,6 @@ fn parse_unnamed_requirement<Url: UnnamedRequirementUrl>(
     // wsp*
     cursor.eat_whitespace();
     if let Some((pos, char)) = cursor.next() {
-        if marker.is_none() {
-            if let Some(given) = url.given() {
-                for c in [';', '#'] {
-                    if given.ends_with(c) {
-                        return Err(Pep508Error {
-                            message: Pep508ErrorSource::String(format!(
-                                "Missing space before '{c}', the end of the URL is ambiguous"
-                            )),
-                            start: requirement_end - c.len_utf8(),
-                            len: c.len_utf8(),
-                            input: cursor.to_string(),
-                        });
-                    }
-                }
-            }
-        }
         let message = if marker.is_none() {
             format!(r#"Expected end of input or `;`, found `{char}`"#)
         } else {
@@ -430,6 +413,19 @@ fn parse_unnamed_url<Url: UnnamedRequirementUrl>(
         });
     }
 
+    for c in [';', '#'] {
+        if url.ends_with(c) {
+            return Err(Pep508Error {
+                message: Pep508ErrorSource::String(format!(
+                    "Missing space before '{c}', the end of the URL is ambiguous"
+                )),
+                start: start + len - 1,
+                len: 1,
+                input: cursor.to_string(),
+            });
+        }
+    }
+
     let url = preprocess_unnamed_url(url, working_dir, cursor, start, len)?;
 
     Ok(url)

crates/uv/tests/it/pip_install.rs

@@ -295,6 +295,31 @@ dependencies = ["flask==1.0.x"]
     Ok(())
 }
 
+#[test]
+fn trailing_semicolon() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.write_str("./flask.whl; sys_platform == 'win32'")?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("-r")
+        .arg("requirements.txt")
+        .arg("--strict"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Couldn't parse requirement in `requirements.txt` at position 0
+      Caused by: Missing space before ';', the end of the URL is ambiguous
+    ./flask.whl; sys_platform == 'win32'
+               ^
+    "###
+    );
+
+    Ok(())
+}
+
 #[test]
 fn missing_pip() {
     uv_snapshot!(Command::new(get_bin()).arg("install"), @r###"