windows fixes, error improvements

crates/compiler/builtins/build.rs

@@ -223,7 +223,11 @@ fn run_command(mut command: Command, flaky_fail_counter: usize) {
                         run_command(command, flaky_fail_counter + 1)
                     }
                 } else {
-                    panic!("{} failed: {}", command_str, error_str);
+                    if error_str.contains("lld-link: error: failed to write the output file: Permission denied") {
+                        panic!("{} failed with:\n\n  {}\n\nWorkaround:\n\n  Re-run the cargo command that triggered this build.", command_str, error_str);
+                    } else {
+                        panic!("{} failed with:\n\n  {}\n", command_str, error_str);
+                    }
                 }
             }
         },

crates/compiler/fmt/src/lib.rs

@@ -13,6 +13,12 @@ pub mod spaces;
 use bumpalo::{collections::String, Bump};
 use roc_parse::ast::Module;
 
+#[cfg(windows)]
+const NEWLINE: &str = "\r\n";
+#[cfg(not(windows))]
+const NEWLINE: &str = "\n";
+
+
 #[derive(Debug)]
 pub struct Ast<'a> {
     pub module: Module<'a>,
@@ -99,7 +105,9 @@ impl<'a> Buf<'a> {
 
     pub fn newline(&mut self) {
         self.spaces_to_flush = 0;
-        self.text.push('\n');
+
+        self.text.push_str(NEWLINE);
+
         self.beginning_of_line = true;
     }
 
@@ -183,14 +191,14 @@ fn fmt_text_eof(text: &mut bumpalo::collections::String<'_>) {
             // There's some whitespace at the end of this file, but the first
             // whitespace char after the last non-whitespace char isn't a newline.
             // So replace that whitespace char (and everything after it) with a newline.
-            text.replace_range(last_whitespace_index.., "\n");
+            text.replace_range(last_whitespace_index.., NEWLINE);
         }
         None => {
             debug_assert!(last_whitespace_index == text.len());
             debug_assert!(!text.ends_with(char::is_whitespace));
 
             // This doesn't end in whitespace at all, so add a newline.
-            text.push('\n');
+            text.push_str(NEWLINE);
         }
     }
 }