Auto merge of #18167 - SomeoneToIgnore:fat-completions, r=Veykril

internal: Send less data during `textDocument/completion` if possible

Similar to https://github.com/rust-lang/rust-analyzer/pull/15522, stops sending extra data during `textDocument/completion` if that data was set in the client completions resolve capabilities, and sends those only during `completionItem/resolve` requests.
Currently, rust-analyzer sends back all fields (including potentially huge docs) for every completion item which might get large.

Same as the other one, this PR aims to keep the changes minimal and does not remove extra computations for such fields — instead, it just filters them out before sending to the client.

The PR omits primitive, boolean and integer, types such as `deprecated`, `preselect`, `insertTextFormat`, `insertTextMode`, etc.  AND `additionalTextEdits` — this one looks very dangerous to compute for each completion item (as the spec says we ought to if there's no corresponding resolve capabilities provided) due to the diff computations and the fact that this code had been in the resolution for some time.
It would be good to resolve this lazily too, please let me know if it's ok to do.

When tested with Zed which only defines `documentation` and `additionalTextEdits` in its client completion resolve capabilities, rust-analyzer starts to send almost 3 times less characters:

Request:
```json
{"jsonrpc":"2.0","id":104,"method":"textDocument/completion","params":{"textDocument":{"uri":"file:///Users/someonetoignore/work/rust-analyzer/crates/ide/src/inlay_hints.rs"},"position":{"line":90,"character":14},"context":{"triggerKind":1}}}
```

<img width="1338" alt="image" src="https://github.com/user-attachments/assets/104f19b5-7095-4fc1-b008-5d829623b2e2">

Before: 381944 characters
[before.json](https://github.com/user-attachments/files/17092385/before.json)

After: 140503 characters
[after.json](https://github.com/user-attachments/files/17092386/after.json)

After Zed's [patch](https://github.com/zed-industries/zed/pull/18212) to enable all resolving possible: 84452 characters
[after-after.json](https://github.com/user-attachments/files/17092755/after-after.json)

3 files changed, 30 insertions, 3 deletions

diff --git a/src/tools/rust-analyzer/crates/ide-completion/src/config.rs b/src/tools/rust-analyzer/crates/ide-completion/src/config.rs
index 0d403f49b7a..1d05419c96d 100644
--- a/src/tools/rust-analyzer/crates/ide-completion/src/config.rs
+++ b/src/tools/rust-analyzer/crates/ide-completion/src/config.rs
@@ -7,7 +7,7 @@
 use hir::ImportPathConfig;
 use ide_db::{imports::insert_use::InsertUseConfig, SnippetCap};
 
-use crate::snippet::Snippet;
+use crate::{snippet::Snippet, CompletionFieldsToResolve};
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct CompletionConfig {
@@ -27,6 +27,7 @@ pub struct CompletionConfig {
     pub prefer_absolute: bool,
     pub snippets: Vec<Snippet>,
     pub limit: Option<usize>,
+    pub fields_to_resolve: CompletionFieldsToResolve,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
diff --git a/src/tools/rust-analyzer/crates/ide-completion/src/lib.rs b/src/tools/rust-analyzer/crates/ide-completion/src/lib.rs
index 58d1fad0950..a78976d3fd8 100644
--- a/src/tools/rust-analyzer/crates/ide-completion/src/lib.rs
+++ b/src/tools/rust-analyzer/crates/ide-completion/src/lib.rs
@@ -37,6 +37,31 @@ pub use crate::{
     snippet::{Snippet, SnippetScope},
 };
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct CompletionFieldsToResolve {
+    pub resolve_label_details: bool,
+    pub resolve_tags: bool,
+    pub resolve_detail: bool,
+    pub resolve_documentation: bool,
+    pub resolve_filter_text: bool,
+    pub resolve_text_edit: bool,
+    pub resolve_command: bool,
+}
+
+impl CompletionFieldsToResolve {
+    pub const fn empty() -> Self {
+        Self {
+            resolve_label_details: false,
+            resolve_tags: false,
+            resolve_detail: false,
+            resolve_documentation: false,
+            resolve_filter_text: false,
+            resolve_text_edit: false,
+            resolve_command: false,
+        }
+    }
+}
+
 //FIXME: split the following feature into fine-grained features.
 
 // Feature: Magic Completions
diff --git a/src/tools/rust-analyzer/crates/ide-completion/src/tests.rs b/src/tools/rust-analyzer/crates/ide-completion/src/tests.rs
index 9d77d970071..f371012de3f 100644
--- a/src/tools/rust-analyzer/crates/ide-completion/src/tests.rs
+++ b/src/tools/rust-analyzer/crates/ide-completion/src/tests.rs
@@ -37,8 +37,8 @@ use test_fixture::ChangeFixture;
 use test_utils::assert_eq_text;
 
 use crate::{
-    resolve_completion_edits, CallableSnippets, CompletionConfig, CompletionItem,
-    CompletionItemKind,
+    resolve_completion_edits, CallableSnippets, CompletionConfig, CompletionFieldsToResolve,
+    CompletionItem, CompletionItemKind,
 };
 
 /// Lots of basic item definitions
@@ -84,6 +84,7 @@ pub(crate) const TEST_CONFIG: CompletionConfig = CompletionConfig {
     prefer_absolute: false,
     snippets: Vec::new(),
     limit: None,
+    fields_to_resolve: CompletionFieldsToResolve::empty(),
 };
 
 pub(crate) fn completion_list(ra_fixture: &str) -> String {