cli --config global option: allow spaces around =

This is especially useful for complicated options like

```
--config 'revsets."immutable_heads()" = "none()"'
```

CHANGELOG.md

@@ -89,6 +89,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   reversing colors rather than underlining, you can set
   `colors."diff token"={ underline = false, reverse = true }` in your config.
 
+* The `--config` global option now allows whitespace around the equals sign, e.g.
+  `--config 'revsets."immutable_heads()" = "none()"'` is now legal.
+
 ### Fixed bugs
 
 * `jj log -p --stat` now shows diff stats as well as the default color-words/git

cli/src/config.rs

@@ -579,7 +579,9 @@ fn parse_config_arg_item(item_str: &str) -> Result<(ConfigNamePathBuf, ConfigVal
     let split_candidates = item_str.as_bytes().iter().positions(|&b| b == b'=');
     let Some((name, value_str)) = split_candidates
         .map(|p| (&item_str[..p], &item_str[p + 1..]))
-        .map(|(name, value)| name.parse().map(|name| (name, value)))
+        // Trim spaces, similarly to TOML syntax; names or values with spaces would have to be
+        // specified with quotes.
+        .map(|(name, value)| name.trim().parse().map(|name| (name, value.trim())))
         .find_or_last(Result::is_ok)
         .transpose()
         .map_err(|err| config_error_with_message("--config name cannot be parsed", err))?
@@ -827,21 +829,38 @@ mod tests {
         assert!(parse_config_arg_item("").is_err());
         assert!(parse_config_arg_item("a").is_err());
         assert!(parse_config_arg_item("=").is_err());
-        // The value parser is sensitive to leading whitespaces, which seems
-        // good because the parsing falls back to a bare string.
-        assert!(parse_config_arg_item("a = 'b'").is_err());
 
         let (name, value) = parse_config_arg_item("a=b").unwrap();
         assert_eq!(name, ConfigNamePathBuf::from_iter(["a"]));
         assert_eq!(value.as_str(), Some("b"));
 
+        let (name, value) = parse_config_arg_item("a = b").unwrap();
+        assert_eq!(name, ConfigNamePathBuf::from_iter(["a"]));
+        assert_eq!(value.as_str(), Some("b"));
+
+        let (name, value) = parse_config_arg_item("a = 'b'").unwrap();
+        assert_eq!(name, ConfigNamePathBuf::from_iter(["a"]));
+        assert_eq!(value.as_str(), Some("b"));
+
+        let (name, value) = parse_config_arg_item("a = ' '").unwrap();
+        assert_eq!(name, ConfigNamePathBuf::from_iter(["a"]));
+        assert_eq!(value.as_str(), Some(" "));
+
+        let (name, value) =
+            parse_config_arg_item(r#"revsets."immutable_heads()" = "none()""#).unwrap();
+        assert_eq!(
+            name,
+            ConfigNamePathBuf::from_iter(["revsets", "immutable_heads()"])
+        );
+        assert_eq!(value.as_str(), Some("none()"));
+
         let (name, value) = parse_config_arg_item("a=").unwrap();
         assert_eq!(name, ConfigNamePathBuf::from_iter(["a"]));
         assert_eq!(value.as_str(), Some(""));
 
         let (name, value) = parse_config_arg_item("a= ").unwrap();
         assert_eq!(name, ConfigNamePathBuf::from_iter(["a"]));
-        assert_eq!(value.as_str(), Some(" "));
+        assert_eq!(value.as_str(), Some(""));
 
         // This one is a bit cryptic, but b=c can be a bare string.
         let (name, value) = parse_config_arg_item("a=b=c").unwrap();

cli/tests/test_global_opts.rs

@@ -462,6 +462,14 @@ fn test_color_config() {
     [EOF]
     ");
 
+    // Spaces around the = signs or dots are OK, by analogy with TOML
+    let output = work_dir.run_jj(["--config= ui . color = never", "log", "-T", "commit_id"]);
+    insta::assert_snapshot!(output, @r"
+    @  230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    ◆  0000000000000000000000000000000000000000
+    [EOF]
+    ");
+
     // --color overrides --config 'ui.color=...'.
     let output = work_dir.run_jj([
         "--color",

docs/config.md

@@ -1573,7 +1573,6 @@ to specify additional configuration settings. This overrides settings defined in
 config files or environment variables. For example,
 
 ```shell
-# Must not have spaces around the `=`
 jj --config ui.color=always --config ui.diff-editor=meld split
 ```