Fix #2104: fmt incorrectly using 1-indexing for columns (#2106)

* Fix #2104: fmt incorrectly using 1-indexing for columns

* Clippy...

packages/autofmt/src/prettier_please.rs

@@ -0,0 +1,66 @@
+use prettyplease::unparse;
+use syn::{Expr, File, Item};
+
+/// Unparse an expression back into a string
+///
+/// This creates a new temporary file, parses the expression into it, and then formats the file.
+/// This is a bit of a hack, but dtonlay doesn't want to support this very simple usecase, forcing us to clone the expr
+pub fn unparse_expr(expr: &Expr) -> String {
+    let file = wrapped(expr);
+    let wrapped = unparse(&file);
+    unwrapped(wrapped)
+}
+
+// Split off the fn main and then cut the tabs off the front
+fn unwrapped(raw: String) -> String {
+    raw.strip_prefix("fn main() {\n")
+        .unwrap()
+        .strip_suffix("}\n")
+        .unwrap()
+        .lines()
+        .map(|line| line.strip_prefix("    ").unwrap()) // todo: set this to tab level
+        .collect::<Vec<_>>()
+        .join("\n")
+}
+
+fn wrapped(expr: &Expr) -> File {
+    File {
+        shebang: None,
+        attrs: vec![],
+        items: vec![
+            //
+            Item::Verbatim(quote::quote! {
+                fn main() {
+                    #expr
+                }
+            }),
+        ],
+    }
+}
+
+#[test]
+fn unparses_raw() {
+    let expr = syn::parse_str("1 + 1").unwrap();
+    let unparsed = unparse(&wrapped(&expr));
+    assert_eq!(unparsed, "fn main() {\n    1 + 1\n}\n");
+}
+
+#[test]
+fn unparses_completely() {
+    let expr = syn::parse_str("1 + 1").unwrap();
+    let unparsed = unparse_expr(&expr);
+    assert_eq!(unparsed, "1 + 1");
+}
+
+#[test]
+fn weird_ifcase() {
+    let contents = r##"
+    fn main() {
+        move |_| timer.with_mut(|t| if t.started_at.is_none() { Some(Instant::now()) } else { None })
+    }
+"##;
+
+    let expr: File = syn::parse_file(contents).unwrap();
+    let out = unparse(&expr);
+    println!("{}", out);
+}