Allow optional `=` for editables in `requirements.txt` (#10954)

## Summary

We allow this for all other argument flags; seems like an oversight.

Closes https://github.com/astral-sh/uv/issues/10941.

crates/uv-requirements-txt/src/lib.rs

@@ -536,7 +536,19 @@ fn parse_entry(
             end,
         }
     } else if s.eat_if("-e") || s.eat_if("--editable") {
+        if s.eat_if('=') {
+            // Explicit equals sign.
+        } else if s.eat_if(char::is_whitespace) {
+            // Key and value are separated by whitespace instead.
             s.eat_whitespace();
+        } else {
+            let (line, column) = calculate_row_column(content, s.cursor());
+            return Err(RequirementsTxtParserError::Parser {
+                message: format!("Expected '=' or whitespace, found {:?}", s.peek()),
+                line,
+                column,
+            });
+        }
 
         let source = if requirements_txt == Path::new("-") {
             None
@@ -851,10 +863,10 @@ fn parse_value<'a, T>(
     while_pattern: impl Pattern<T>,
 ) -> Result<&'a str, RequirementsTxtParserError> {
     if s.eat_if('=') {
-        // Explicit equals sign
+        // Explicit equals sign.
         Ok(s.eat_while(while_pattern).trim_end())
     } else if s.eat_if(char::is_whitespace) {
-        // Key and value are separated by whitespace instead
+        // Key and value are separated by whitespace instead.
         s.eat_whitespace();
         Ok(s.eat_while(while_pattern).trim_end())
     } else {

crates/uv/tests/it/pip_install.rs

@@ -1302,6 +1302,60 @@ fn install_editable_pep_508_requirements_txt() -> Result<()> {
     "###
     );
 
+    requirements_txt.write_str(&indoc::formatdoc! {r"
+        --editable black[d] @ file://{workspace_root}/scripts/packages/black_editable
+        ",
+        workspace_root = context.workspace_root.simplified_display(),
+    })?;
+
+    uv_snapshot!(context.filters(), context.pip_install()
+        .arg("-r")
+        .arg("requirements.txt"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Audited 1 package in [TIME]
+    "###
+    );
+
+    requirements_txt.write_str(&indoc::formatdoc! {r"
+        --editable=black[d] @ file://{workspace_root}/scripts/packages/black_editable
+        ",
+        workspace_root = context.workspace_root.simplified_display(),
+    })?;
+
+    uv_snapshot!(context.filters(), context.pip_install()
+        .arg("-r")
+        .arg("requirements.txt"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Audited 1 package in [TIME]
+    "###
+    );
+
+    requirements_txt.write_str(&indoc::formatdoc! {r"
+        --editable= black[d] @ file://{workspace_root}/scripts/packages/black_editable
+        ",
+        workspace_root = context.workspace_root.simplified_display(),
+    })?;
+
+    uv_snapshot!(context.filters(), context.pip_install()
+        .arg("-r")
+        .arg("requirements.txt"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Audited 1 package in [TIME]
+    "###
+    );
+
     Ok(())
 }