Add format_cargo_toml to the code path called by rustfmt

Now users can provide the path to their `Cargo.toml` files for rustfmt
to format.

Author: ytmimi

src/formatting.rs

@@ -1,7 +1,9 @@
 // High level formatting functions.
 
 use std::collections::HashMap;
+use std::ffi::OsStr;
 use std::io::{self, Write};
+use std::path::PathBuf;
 use std::rc::Rc;
 use std::time::{Duration, Instant};
 
@@ -13,6 +15,7 @@ use self::newline_style::apply_newline_style;
 use crate::comment::{CharClasses, FullCodeCharKind};
 use crate::config::{Config, FileName, Verbosity};
 use crate::formatting::generated::is_generated_file;
+use crate::ignore_path::IgnorePathSet;
 use crate::issues::BadIssueSeeker;
 use crate::modules::Module;
 use crate::parse::parser::{DirectoryOwnership, Parser, ParserError};
@@ -39,6 +42,15 @@ impl<'b, T: Write + 'b> Session<'b, T> {
             return Err(ErrorKind::VersionMismatch);
         }
 
+        let cargo_toml = Some(OsStr::new("Cargo.toml"));
+        match input {
+            Input::File(path) if path.file_name() == cargo_toml => {
+                let config = &self.config.clone();
+                return format_cargo_toml(path, config, self);
+            }
+            _ => {}
+        }
+
         rustc_span::create_session_if_not_set_then(self.config.edition().into(), |_| {
             if self.config.disable_all_formatting() {
                 // When the input is from stdin, echo back the input.
@@ -164,6 +176,29 @@ fn format_project<T: FormatHandler>(
     Ok(context.report)
 }
 
+fn format_cargo_toml<T: FormatHandler>(
+    path: PathBuf,
+    config: &Config,
+    handler: &mut T,
+) -> Result<FormatReport, ErrorKind> {
+    let mut report = FormatReport::new();
+
+    let ignore_path_set = IgnorePathSet::from_ignore_list(&config.ignore())?;
+    let file_name = FileName::Real(path.clone());
+    if ignore_path_set.is_match(&file_name) {
+        return Ok(report);
+    }
+
+    let input = std::fs::read_to_string(&path)?;
+    let mut result = cargo_toml::format_cargo_toml_inner(&input, config)?;
+
+    apply_newline_style(config.newline_style(), &mut result, &input);
+
+    handler.handle_formatted_file(None, file_name, result, &mut report)?;
+
+    Ok(report)
+}
+
 // Used for formatting files.
 #[derive(new)]
 struct FormatContext<'a, T: FormatHandler> {
@@ -232,7 +267,7 @@ impl<'a, T: FormatHandler + 'a> FormatContext<'a, T> {
             .add_non_formatted_ranges(visitor.skipped_range.borrow().clone());
 
         self.handler.handle_formatted_file(
-            &self.parse_session,
+            Some(&self.parse_session),
             path,
             visitor.buffer.to_owned(),
             &mut self.report,
@@ -244,7 +279,7 @@ impl<'a, T: FormatHandler + 'a> FormatContext<'a, T> {
 trait FormatHandler {
     fn handle_formatted_file(
         &mut self,
-        parse_session: &ParseSess,
+        parse_session: Option<&ParseSess>,
         path: FileName,
         result: String,
         report: &mut FormatReport,
@@ -255,14 +290,14 @@ impl<'b, T: Write + 'b> FormatHandler for Session<'b, T> {
     // Called for each formatted file.
     fn handle_formatted_file(
         &mut self,
-        parse_session: &ParseSess,
+        parse_session: Option<&ParseSess>,
         path: FileName,
         result: String,
         report: &mut FormatReport,
     ) -> Result<(), ErrorKind> {
         if let Some(ref mut out) = self.out {
             match source_file::write_file(
-                Some(parse_session),
+                parse_session,
                 &path,
                 &result,
                 out,

src/formatting/cargo_toml.rs

@@ -1,12 +1,13 @@
 use itertools::Itertools;
 use std::cmp::Ordering;
-use toml_edit::{visit_mut::*, Decor, Document, Formatted, Item, KeyMut, Table, TableLike, Value};
+use toml_edit::{
+    visit_mut::*, Decor, Document, Formatted, Item, KeyMut, Table, TableLike, TomlError, Value,
+};
 
-use crate::Config;
+use crate::{Config, ErrorKind};
 
-#[allow(dead_code)]
-fn format_cargo_toml(content: &str, config: &Config) -> String {
-    let mut doc = content.parse::<toml_edit::Document>().unwrap();
+pub(crate) fn format_cargo_toml_inner(content: &str, config: &Config) -> Result<String, ErrorKind> {
+    let mut doc = content.parse::<toml_edit::Document>()?;
     let rules: Vec<Box<dyn VisitMut>> = vec![
         Box::new(SortSection {
             current_position: 0,
@@ -27,7 +28,14 @@ fn format_cargo_toml(content: &str, config: &Config) -> String {
     for mut rule in rules.into_iter() {
         rule.visit_document_mut(&mut doc);
     }
-    return doc.to_string();
+
+    Ok(doc.to_string())
+}
+
+impl From<TomlError> for ErrorKind {
+    fn from(_: TomlError) -> Self {
+        ErrorKind::ParseError
+    }
 }
 
 /// Sort key names alphabetically within each section, with the exception of the
@@ -363,7 +371,7 @@ mod tests {
         d = "git-rustfmt"
         c = "src/git-rustfmt/main.rs""#;
 
-        let formatted = format_cargo_toml(s, &Default::default());
+        let formatted = format_cargo_toml_inner(s, &Default::default()).unwrap();
 
         #[rustfmt::skip]
         let expected = r#"[package]