Auto merge of #18075 - roife:fix-issue-17858, r=Veykril

feat: render patterns in params for hovering

Fix #17858

This PR introduces an option to [hir-def/src/body/pretty.rs](https://github.com/rust-lang/rust-analyzer/blob/08c7bbc2dbe4dcc8968484f1a0e1e6fe7a1d4f6d/crates/hir-def/src/body/pretty.rs) to render the result as a single line, which is then reused for rendering patterns in parameters for hovering.

Author: bors

crates/hir-def/src/body.rs

@@ -227,6 +227,17 @@ impl Body {
         pretty::print_expr_hir(db, self, owner, expr, edition)
     }
 
+    pub fn pretty_print_pat(
+        &self,
+        db: &dyn DefDatabase,
+        owner: DefWithBodyId,
+        pat: PatId,
+        oneline: bool,
+        edition: Edition,
+    ) -> String {
+        pretty::print_pat_hir(db, self, owner, pat, oneline, edition)
+    }
+
     fn new(
         db: &dyn DefDatabase,
         owner: DefWithBodyId,

crates/hir-def/src/body/pretty.rs

@@ -16,6 +16,13 @@ use crate::{
 
 use super::*;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(super) enum LineFormat {
+    Oneline,
+    Newline,
+    Indentation,
+}
+
 pub(super) fn print_body_hir(
     db: &dyn DefDatabase,
     body: &Body,
@@ -52,7 +59,14 @@ pub(super) fn print_body_hir(
         }
     };
 
-    let mut p = Printer { db, body, buf: header, indent_level: 0, needs_indent: false, edition };
+    let mut p = Printer {
+        db,
+        body,
+        buf: header,
+        indent_level: 0,
+        line_format: LineFormat::Newline,
+        edition,
+    };
     if let DefWithBodyId::FunctionId(it) = owner {
         p.buf.push('(');
         let function_data = &db.function_data(it);
@@ -95,12 +109,38 @@ pub(super) fn print_expr_hir(
     expr: ExprId,
     edition: Edition,
 ) -> String {
-    let mut p =
-        Printer { db, body, buf: String::new(), indent_level: 0, needs_indent: false, edition };
+    let mut p = Printer {
+        db,
+        body,
+        buf: String::new(),
+        indent_level: 0,
+        line_format: LineFormat::Newline,
+        edition,
+    };
     p.print_expr(expr);
     p.buf
 }
 
+pub(super) fn print_pat_hir(
+    db: &dyn DefDatabase,
+    body: &Body,
+    _owner: DefWithBodyId,
+    pat: PatId,
+    oneline: bool,
+    edition: Edition,
+) -> String {
+    let mut p = Printer {
+        db,
+        body,
+        buf: String::new(),
+        indent_level: 0,
+        line_format: if oneline { LineFormat::Oneline } else { LineFormat::Newline },
+        edition,
+    };
+    p.print_pat(pat);
+    p.buf
+}
+
 macro_rules! w {
     ($dst:expr, $($arg:tt)*) => {
         { let _ = write!($dst, $($arg)*); }
@@ -109,10 +149,10 @@ macro_rules! w {
 
 macro_rules! wln {
     ($dst:expr) => {
-        { let _ = writeln!($dst); }
+        { $dst.newline(); }
     };
     ($dst:expr, $($arg:tt)*) => {
-        { let _ = writeln!($dst, $($arg)*); }
+        { let _ = w!($dst, $($arg)*); $dst.newline(); }
     };
 }
 
@@ -121,24 +161,30 @@ struct Printer<'a> {
     body: &'a Body,
     buf: String,
     indent_level: usize,
-    needs_indent: bool,
+    line_format: LineFormat,
     edition: Edition,
 }
 
 impl Write for Printer<'_> {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         for line in s.split_inclusive('\n') {
-            if self.needs_indent {
+            if matches!(self.line_format, LineFormat::Indentation) {
                 match self.buf.chars().rev().find(|ch| *ch != ' ') {
                     Some('\n') | None => {}
                     _ => self.buf.push('\n'),
                 }
                 self.buf.push_str(&"    ".repeat(self.indent_level));
-                self.needs_indent = false;
             }
 
             self.buf.push_str(line);
-            self.needs_indent = line.ends_with('\n');
+
+            if matches!(self.line_format, LineFormat::Newline | LineFormat::Indentation) {
+                self.line_format = if line.ends_with('\n') {
+                    LineFormat::Indentation
+                } else {
+                    LineFormat::Newline
+                };
+            }
         }
 
         Ok(())
@@ -161,14 +207,28 @@ impl Printer<'_> {
         }
     }
 
+    // Add a newline if the current line is not empty.
+    // If the current line is empty, add a space instead.
+    //
+    // Do not use [`writeln!()`] or [`wln!()`] here, which will result in
+    // infinite recursive calls to this function.
     fn newline(&mut self) {
-        match self.buf.chars().rev().find_position(|ch| *ch != ' ') {
-            Some((_, '\n')) | None => {}
-            Some((idx, _)) => {
-                if idx != 0 {
-                    self.buf.drain(self.buf.len() - idx..);
+        if matches!(self.line_format, LineFormat::Oneline) {
+            match self.buf.chars().last() {
+                Some(' ') | None => {}
+                Some(_) => {
+                    w!(self, " ");
+                }
+            }
+        } else {
+            match self.buf.chars().rev().find_position(|ch| *ch != ' ') {
+                Some((_, '\n')) | None => {}
+                Some((idx, _)) => {
+                    if idx != 0 {
+                        self.buf.drain(self.buf.len() - idx..);
+                    }
+                    w!(self, "\n");
                 }
-                writeln!(self).unwrap()
             }
         }
     }
@@ -539,12 +599,14 @@ impl Printer<'_> {
                 w!(self, ")");
             }
             Pat::Or(pats) => {
+                w!(self, "(");
                 for (i, pat) in pats.iter().enumerate() {
                     if i != 0 {
                         w!(self, " | ");
                     }
                     self.print_pat(*pat);
                 }
+                w!(self, ")");
             }
             Pat::Record { path, args, ellipsis } => {
                 match path {
@@ -554,12 +616,37 @@ impl Printer<'_> {
 
                 w!(self, " {{");
                 let edition = self.edition;
+                let oneline = matches!(self.line_format, LineFormat::Oneline);
                 self.indented(|p| {
-                    for arg in args.iter() {
-                        w!(p, "{}: ", arg.name.display(self.db.upcast(), edition));
-                        p.print_pat(arg.pat);
-                        wln!(p, ",");
+                    for (idx, arg) in args.iter().enumerate() {
+                        let field_name = arg.name.display(self.db.upcast(), edition).to_string();
+
+                        let mut same_name = false;
+                        if let Pat::Bind { id, subpat: None } = &self.body[arg.pat] {
+                            if let Binding { name, mode: BindingAnnotation::Unannotated, .. } =
+                                &self.body.bindings[*id]
+                            {
+                                if name.as_str() == field_name {
+                                    same_name = true;
+                                }
+                            }
+                        }
+
+                        w!(p, "{}", field_name);
+
+                        if !same_name {
+                            w!(p, ": ");
+                            p.print_pat(arg.pat);
+                        }
+
+                        // Do not print the extra comma if the line format is oneline
+                        if oneline && idx == args.len() - 1 {
+                            w!(p, " ");
+                        } else {
+                            wln!(p, ",");
+                        }
                     }
+
                     if *ellipsis {
                         wln!(p, "..");
                     }

crates/hir/src/display.rs

@@ -99,17 +99,20 @@ impl HirDisplay for Function {
         }
 
         // FIXME: Use resolved `param.ty` once we no longer discard lifetimes
+        let body = db.body(self.id.into());
         for (type_ref, param) in data.params.iter().zip(self.assoc_fn_params(db)).skip(skip_self) {
-            let local = param.as_local(db).map(|it| it.name(db));
             if !first {
                 f.write_str(", ")?;
             } else {
                 first = false;
             }
-            match local {
-                Some(name) => write!(f, "{}: ", name.display(f.db.upcast(), f.edition()))?,
-                None => f.write_str("_: ")?,
-            }
+
+            let pat_id = body.params[param.idx - body.self_param.is_some() as usize];
+            let pat_str =
+                body.pretty_print_pat(db.upcast(), self.id.into(), pat_id, true, f.edition());
+            f.write_str(&pat_str)?;
+
+            f.write_str(": ")?;
             type_ref.hir_fmt(f)?;
         }