Merge #11145

11145: feat: add config to use reasonable default expression instead of todo! when filling missing fields r=Veykril a=bnjjj

Use `Default::default()` in struct fields when we ask to fill it instead of putting `todo!()` for every fields

before:

```rust
pub enum Other {
    One,
    Two,
}

pub struct Test {
    text: String,
    num: usize,
    other: Other,
}

fn t_test() {
    let test = Test {<|>};
}
``` 

after: 

```rust
pub enum Other {
    One,
    Two,
}

pub struct Test {
    text: String,
    num: usize,
    other: Other,
}

fn t_test() {
    let test = Test {
        text: String::new(),
        num: 0,
        other: todo!(),
    };
}
``` 



Co-authored-by: Benjamin Coenen <5719034+bnjjj@users.noreply.github.com>
Co-authored-by: Coenen Benjamin <benjamin.coenen@hotmail.com>

crates/rust-analyzer/src/config.rs

@@ -11,8 +11,8 @@ use std::{ffi::OsString, iter, path::PathBuf};
 
 use flycheck::FlycheckConfig;
 use ide::{
-    AssistConfig, CompletionConfig, DiagnosticsConfig, HighlightRelatedConfig, HoverConfig,
-    HoverDocFormat, InlayHintsConfig, JoinLinesConfig, Snippet, SnippetScope,
+    AssistConfig, CompletionConfig, DiagnosticsConfig, ExprFillDefaultMode, HighlightRelatedConfig,
+    HoverConfig, HoverDocFormat, InlayHintsConfig, JoinLinesConfig, Snippet, SnippetScope,
 };
 use ide_db::helpers::{
     insert_use::{ImportGranularity, InsertUseConfig, PrefixKind},
@@ -45,6 +45,8 @@ use crate::{
 // parsing the old name.
 config_data! {
     struct ConfigData {
+        /// Placeholder for missing expressions in assists.
+        assist_exprFillDefault: ExprFillDefaultDef              = "\"todo\"",
         /// How imports should be grouped into use statements.
         assist_importGranularity |
         assist_importMergeBehavior |
@@ -708,6 +710,10 @@ impl Config {
         DiagnosticsConfig {
             disable_experimental: !self.data.diagnostics_enableExperimental,
             disabled: self.data.diagnostics_disabled.clone(),
+            expr_fill_default: match self.data.assist_exprFillDefault {
+                ExprFillDefaultDef::Todo => ExprFillDefaultMode::Todo,
+                ExprFillDefaultDef::Default => ExprFillDefaultMode::Default,
+            },
         }
     }
     pub fn diagnostics_map(&self) -> DiagnosticsMapConfig {
@@ -1079,6 +1085,15 @@ enum ManifestOrProjectJson {
     ProjectJson(ProjectJsonData),
 }
 
+#[derive(Deserialize, Debug, Clone)]
+#[serde(rename_all = "snake_case")]
+pub enum ExprFillDefaultDef {
+    #[serde(alias = "todo")]
+    Todo,
+    #[serde(alias = "default")]
+    Default,
+}
+
 #[derive(Deserialize, Debug, Clone)]
 #[serde(rename_all = "snake_case")]
 enum ImportGranularityDef {
@@ -1285,6 +1300,14 @@ fn field_props(field: &str, ty: &str, doc: &[&str], default: &str) -> serde_json
                 "Merge imports from the same module into a single `use` statement."
             ],
         },
+        "ExprFillDefaultDef" => set! {
+            "type": "string",
+            "enum": ["todo", "default"],
+            "enumDescriptions": [
+                "Fill missing expressions with the `todo` macro",
+                "Fill missing expressions with reasonable defaults, `new` or `default` constructors."
+            ],
+        },
         "ImportGranularityDef" => set! {
             "type": "string",
             "enum": ["preserve", "crate", "module", "item"],