Auto merge of rust-lang#13216 - DesmondWillowbrook:move_format_string…

…_arg, r=DesmondWillowbrook

New assist: move_format_string_arg

The name might need some improving.

```rust
fn main() {
    print!("{x + 1}");
}
```
to
```rust
fn main() {
    print!("{}"$0, x + 1);
}
```

fixes rust-lang#13180

ref to rust-lang#5988 for similar work

* extracted `format_like`'s parser to it's own module in `ide-db`
* reworked the parser's API to be more direct
* added assist to extract expressions in format args

crates/ide-assists/src/handlers/move_format_string_arg.rs

@@ -0,0 +1,268 @@
+use crate::{AssistContext, Assists};
+use ide_db::{
+    assists::{AssistId, AssistKind},
+    syntax_helpers::{
+        format_string::is_format_string,
+        format_string_exprs::{parse_format_exprs, Arg},
+    },
+};
+use itertools::Itertools;
+use syntax::{ast, AstNode, AstToken, NodeOrToken, SyntaxKind::COMMA, TextRange};
+
+// Assist: move_format_string_arg
+//
+// Move an expression out of a format string.
+//
+// ```
+// macro_rules! format_args {
+//     ($lit:literal $(tt:tt)*) => { 0 },
+// }
+// macro_rules! print {
+//     ($($arg:tt)*) => (std::io::_print(format_args!($($arg)*)));
+// }
+//
+// fn main() {
+//     print!("{x + 1}$0");
+// }
+// ```
+// ->
+// ```
+// macro_rules! format_args {
+//     ($lit:literal $(tt:tt)*) => { 0 },
+// }
+// macro_rules! print {
+//     ($($arg:tt)*) => (std::io::_print(format_args!($($arg)*)));
+// }
+//
+// fn main() {
+//     print!("{}"$0, x + 1);
+// }
+// ```
+
+pub(crate) fn move_format_string_arg(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let fmt_string = ctx.find_token_at_offset::<ast::String>()?;
+    let tt = fmt_string.syntax().parent().and_then(ast::TokenTree::cast)?;
+
+    let expanded_t = ast::String::cast(
+        ctx.sema.descend_into_macros_with_kind_preference(fmt_string.syntax().clone()),
+    )?;
+    if !is_format_string(&expanded_t) {
+        return None;
+    }
+
+    let (new_fmt, extracted_args) = parse_format_exprs(fmt_string.text()).ok()?;
+    if extracted_args.is_empty() {
+        return None;
+    }
+
+    acc.add(
+        AssistId(
+            "move_format_string_arg",
+            // if there aren't any expressions, then make the assist a RefactorExtract
+            if extracted_args.iter().filter(|f| matches!(f, Arg::Expr(_))).count() == 0 {
+                AssistKind::RefactorExtract
+            } else {
+                AssistKind::QuickFix
+            },
+        ),
+        "Extract format args",
+        tt.syntax().text_range(),
+        |edit| {
+            let fmt_range = fmt_string.syntax().text_range();
+
+            // Replace old format string with new format string whose arguments have been extracted
+            edit.replace(fmt_range, new_fmt);
+
+            // Insert cursor at end of format string
+            edit.insert(fmt_range.end(), "$0");
+
+            // Extract existing arguments in macro
+            let tokens =
+                tt.token_trees_and_tokens().filter_map(NodeOrToken::into_token).collect_vec();
+
+            let mut existing_args: Vec<String> = vec![];
+
+            let mut current_arg = String::new();
+            if let [_opening_bracket, format_string, _args_start_comma, tokens @ .., end_bracket] =
+                tokens.as_slice()
+            {
+                for t in tokens {
+                    if t.kind() == COMMA {
+                        existing_args.push(current_arg.trim().into());
+                        current_arg.clear();
+                    } else {
+                        current_arg.push_str(t.text());
+                    }
+                }
+                existing_args.push(current_arg.trim().into());
+
+                // delete everything after the format string till end bracket
+                // we're going to insert the new arguments later
+                edit.delete(TextRange::new(
+                    format_string.text_range().end(),
+                    end_bracket.text_range().start(),
+                ));
+            }
+
+            // Start building the new args
+            let mut existing_args = existing_args.into_iter();
+            let mut args = String::new();
+
+            let mut placeholder_idx = 1;
+
+            for extracted_args in extracted_args {
+                // remove expr from format string
+                args.push_str(", ");
+
+                match extracted_args {
+                    Arg::Ident(s) | Arg::Expr(s) => {
+                        // insert arg
+                        args.push_str(&s);
+                    }
+                    Arg::Placeholder => {
+                        // try matching with existing argument
+                        match existing_args.next() {
+                            Some(ea) => {
+                                args.push_str(&ea);
+                            }
+                            None => {
+                                // insert placeholder
+                                args.push_str(&format!("${placeholder_idx}"));
+                                placeholder_idx += 1;
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Insert new args
+            edit.insert(fmt_range.end(), args);
+        },
+    );
+
+    Some(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tests::check_assist;
+
+    const MACRO_DECL: &'static str = r#"
+macro_rules! format_args {
+    ($lit:literal $(tt:tt)*) => { 0 },
+}
+macro_rules! print {
+    ($($arg:tt)*) => (std::io::_print(format_args!($($arg)*)));
+}
+"#;
+
+    fn add_macro_decl(s: &'static str) -> String {
+        MACRO_DECL.to_string() + s
+    }
+
+    #[test]
+    fn multiple_middle_arg() {
+        check_assist(
+            move_format_string_arg,
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {x + 1:b} {}$0", y + 2, 2);
+}
+"#,
+            ),
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {:b} {}"$0, y + 2, x + 1, 2);
+}
+"#,
+            ),
+        );
+    }
+
+    #[test]
+    fn single_arg() {
+        check_assist(
+            move_format_string_arg,
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{obj.value:b}$0",);
+}
+"#,
+            ),
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{:b}"$0, obj.value);
+}
+"#,
+            ),
+        );
+    }
+
+    #[test]
+    fn multiple_middle_placeholders_arg() {
+        check_assist(
+            move_format_string_arg,
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {x + 1:b} {} {}$0", y + 2, 2);
+}
+"#,
+            ),
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {:b} {} {}"$0, y + 2, x + 1, 2, $1);
+}
+"#,
+            ),
+        );
+    }
+
+    #[test]
+    fn multiple_trailing_args() {
+        check_assist(
+            move_format_string_arg,
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {x + 1:b} {Struct(1, 2)}$0", 1);
+}
+"#,
+            ),
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {:b} {}"$0, 1, x + 1, Struct(1, 2));
+}
+"#,
+            ),
+        );
+    }
+
+    #[test]
+    fn improper_commas() {
+        check_assist(
+            move_format_string_arg,
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {x + 1:b} {Struct(1, 2)}$0", 1,);
+}
+"#,
+            ),
+            &add_macro_decl(
+                r#"
+fn main() {
+    print!("{} {:b} {}"$0, 1, x + 1, Struct(1, 2));
+}
+"#,
+            ),
+        );
+    }
+}

crates/ide-assists/src/lib.rs

@@ -136,6 +136,7 @@ mod handlers {
     mod flip_binexpr;
     mod flip_comma;
     mod flip_trait_bound;
+    mod move_format_string_arg;
     mod generate_constant;
     mod generate_default_from_enum_variant;
     mod generate_default_from_new;
@@ -254,6 +255,7 @@ mod handlers {
             merge_imports::merge_imports,
             merge_match_arms::merge_match_arms,
             move_bounds::move_bounds_to_where_clause,
+            move_format_string_arg::move_format_string_arg,
             move_guard::move_arm_cond_to_match_guard,
             move_guard::move_guard_to_arm_body,
             move_module_to_file::move_module_to_file,

crates/ide-assists/src/tests/generated.rs

@@ -1591,6 +1591,37 @@ fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
     )
 }
 
+#[test]
+fn doctest_move_format_string_arg() {
+    check_doc_test(
+        "move_format_string_arg",
+        r#####"
+macro_rules! format_args {
+    ($lit:literal $(tt:tt)*) => { 0 },
+}
+macro_rules! print {
+    ($($arg:tt)*) => (std::io::_print(format_args!($($arg)*)));
+}
+
+fn main() {
+    print!("{x + 1}$0");
+}
+"#####,
+        r#####"
+macro_rules! format_args {
+    ($lit:literal $(tt:tt)*) => { 0 },
+}
+macro_rules! print {
+    ($($arg:tt)*) => (std::io::_print(format_args!($($arg)*)));
+}
+
+fn main() {
+    print!("{}"$0, x + 1);
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_move_from_mod_rs() {
     check_doc_test(