diff --git a/crates/ide-completion/src/config.rs b/crates/ide-completion/src/config.rs
index 8f6a97e1e09d8..3d025f284bbb7 100644
--- a/crates/ide-completion/src/config.rs
+++ b/crates/ide-completion/src/config.rs
@@ -14,6 +14,7 @@ pub struct CompletionConfig {
     pub enable_imports_on_the_fly: bool,
     pub enable_self_on_the_fly: bool,
     pub enable_private_editable: bool,
+    pub full_function_signatures: bool,
     pub callable: Option<CallableSnippets>,
     pub snippet_cap: Option<SnippetCap>,
     pub insert_use: InsertUseConfig,
diff --git a/crates/ide-completion/src/render/function.rs b/crates/ide-completion/src/render/function.rs
index 8afce8db5ea86..dfae715afe36d 100644
--- a/crates/ide-completion/src/render/function.rs
+++ b/crates/ide-completion/src/render/function.rs
@@ -98,9 +98,14 @@ fn render(
         _ => (),
     }
 
+    let detail = if ctx.completion.config.full_function_signatures {
+        detail_full(db, func)
+    } else {
+        detail(db, func)
+    };
     item.set_documentation(ctx.docs(func))
         .set_deprecated(ctx.is_deprecated(func) || ctx.is_deprecated_assoc_item(func))
-        .detail(detail(db, func))
+        .detail(detail)
         .lookup_by(name.unescaped().to_smol_str());
 
     match ctx.completion.config.snippet_cap {
@@ -263,6 +268,21 @@ fn detail(db: &dyn HirDatabase, func: hir::Function) -> String {
     detail
 }
 
+fn detail_full(db: &dyn HirDatabase, func: hir::Function) -> String {
+    let signature = format!("{}", func.display(db));
+    let mut detail = String::with_capacity(signature.len());
+
+    for segment in signature.split_whitespace() {
+        if !detail.is_empty() {
+            detail.push(' ');
+        }
+
+        detail.push_str(segment);
+    }
+
+    detail
+}
+
 fn params_display(db: &dyn HirDatabase, func: hir::Function) -> String {
     if let Some(self_param) = func.self_param(db) {
         let assoc_fn_params = func.assoc_fn_params(db);
diff --git a/crates/ide-completion/src/tests.rs b/crates/ide-completion/src/tests.rs
index 2464e8d5f8175..284bdd8af21f8 100644
--- a/crates/ide-completion/src/tests.rs
+++ b/crates/ide-completion/src/tests.rs
@@ -64,6 +64,7 @@ pub(crate) const TEST_CONFIG: CompletionConfig = CompletionConfig {
     enable_imports_on_the_fly: true,
     enable_self_on_the_fly: true,
     enable_private_editable: false,
+    full_function_signatures: false,
     callable: Some(CallableSnippets::FillArguments),
     snippet_cap: SnippetCap::new(true),
     prefer_no_std: false,
diff --git a/crates/ide-completion/src/tests/special.rs b/crates/ide-completion/src/tests/special.rs
index e80a289049f1d..83888e08f1c7b 100644
--- a/crates/ide-completion/src/tests/special.rs
+++ b/crates/ide-completion/src/tests/special.rs
@@ -2,10 +2,15 @@
 
 use expect_test::{expect, Expect};
 
-use crate::tests::{
-    check_edit, completion_list, completion_list_no_kw, completion_list_with_trigger_character,
+use crate::{
+    tests::{
+        check_edit, completion_list, completion_list_no_kw, completion_list_with_trigger_character,
+    },
+    CompletionItemKind,
 };
 
+use super::{do_completion_with_config, TEST_CONFIG};
+
 fn check_no_kw(ra_fixture: &str, expect: Expect) {
     let actual = completion_list_no_kw(ra_fixture);
     expect.assert_eq(&actual)
@@ -1303,3 +1308,67 @@ struct Foo<T: PartialOrd
 "#,
     );
 }
+
+fn check_signatures(src: &str, kind: CompletionItemKind, reduced: Expect, full: Expect) {
+    const FULL_SIGNATURES_CONFIG: crate::CompletionConfig = {
+        let mut x = TEST_CONFIG;
+        x.full_function_signatures = true;
+        x
+    };
+
+    // reduced signature
+    let completion = do_completion_with_config(TEST_CONFIG, src, kind);
+    assert!(completion[0].detail.is_some());
+    reduced.assert_eq(completion[0].detail.as_ref().unwrap());
+
+    // full signature
+    let completion = do_completion_with_config(FULL_SIGNATURES_CONFIG, src, kind);
+    assert!(completion[0].detail.is_some());
+    full.assert_eq(completion[0].detail.as_ref().unwrap());
+}
+
+#[test]
+fn respects_full_function_signatures() {
+    check_signatures(
+        r#"
+pub fn foo<'x, T>(x: &'x mut T) -> u8 where T: Clone, { 0u8 }
+fn main() { fo$0 }
+"#,
+        CompletionItemKind::SymbolKind(ide_db::SymbolKind::Function),
+        expect!("fn(&mut T) -> u8"),
+        expect!("pub fn foo<'x, T>(x: &'x mut T) -> u8 where T: Clone,"),
+    );
+
+    check_signatures(
+        r#"
+struct Foo;
+struct Bar;
+impl Bar {
+    pub const fn baz(x: Foo) -> ! { loop {} };
+}
+
+fn main() { Bar::b$0 }
+"#,
+        CompletionItemKind::SymbolKind(ide_db::SymbolKind::Function),
+        expect!("const fn(Foo) -> !"),
+        expect!("pub const fn baz(x: Foo) -> !"),
+    );
+
+    check_signatures(
+        r#"
+struct Foo;
+struct Bar;
+impl Bar {
+    pub const fn baz<'foo>(&'foo mut self, x: &'foo Foo) -> ! { loop {} };
+}
+
+fn main() {
+    let mut bar = Bar;
+    bar.b$0
+}
+"#,
+        CompletionItemKind::Method,
+        expect!("const fn(&'foo mut self, &Foo) -> !"),
+        expect!("pub const fn baz<'foo>(&'foo mut self, x: &'foo Foo) -> !"),
+    );
+}
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index 7475f061d55bc..cc7f2da532c38 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -217,6 +217,8 @@ config_data! {
         completion_autoself_enable: bool        = "true",
         /// Whether to add parenthesis and argument snippets when completing function.
         completion_callable_snippets: CallableCompletionDef  = "\"fill_arguments\"",
+        /// Whether to show full function/method signatures in completion docs.
+        completion_fullFunctionSignatures_enable: bool = "false",
         /// Maximum number of completions to return. If `None`, the limit is infinite.
         completion_limit: Option<usize> = "null",
         /// Whether to show postfix snippets like `dbg`, `if`, `not`, etc.
@@ -1455,6 +1457,7 @@ impl Config {
                 && completion_item_edit_resolve(&self.caps),
             enable_self_on_the_fly: self.data.completion_autoself_enable,
             enable_private_editable: self.data.completion_privateEditable_enable,
+            full_function_signatures: self.data.completion_fullFunctionSignatures_enable,
             callable: match self.data.completion_callable_snippets {
                 CallableCompletionDef::FillArguments => Some(CallableSnippets::FillArguments),
                 CallableCompletionDef::AddParentheses => Some(CallableSnippets::AddParentheses),
diff --git a/crates/rust-analyzer/src/integrated_benchmarks.rs b/crates/rust-analyzer/src/integrated_benchmarks.rs
index 5a11012b93cf1..2c402552919f0 100644
--- a/crates/rust-analyzer/src/integrated_benchmarks.rs
+++ b/crates/rust-analyzer/src/integrated_benchmarks.rs
@@ -134,6 +134,7 @@ fn integrated_completion_benchmark() {
             enable_imports_on_the_fly: true,
             enable_self_on_the_fly: true,
             enable_private_editable: true,
+            full_function_signatures: false,
             callable: Some(CallableSnippets::FillArguments),
             snippet_cap: SnippetCap::new(true),
             insert_use: InsertUseConfig {
@@ -173,6 +174,7 @@ fn integrated_completion_benchmark() {
             enable_imports_on_the_fly: true,
             enable_self_on_the_fly: true,
             enable_private_editable: true,
+            full_function_signatures: false,
             callable: Some(CallableSnippets::FillArguments),
             snippet_cap: SnippetCap::new(true),
             insert_use: InsertUseConfig {
diff --git a/docs/user/generated_config.adoc b/docs/user/generated_config.adoc
index bde1c03bef7f0..dec7a50757484 100644
--- a/docs/user/generated_config.adoc
+++ b/docs/user/generated_config.adoc
@@ -252,6 +252,11 @@ with `self` prefixed to them when inside a method.
 --
 Whether to add parenthesis and argument snippets when completing function.
 --
+[[rust-analyzer.completion.fullFunctionSignatures.enable]]rust-analyzer.completion.fullFunctionSignatures.enable (default: `false`)::
++
+--
+Whether to show full function/method signatures in completion docs.
+--
 [[rust-analyzer.completion.limit]]rust-analyzer.completion.limit (default: `null`)::
 +
 --
diff --git a/editors/code/package.json b/editors/code/package.json
index 673dc0fcbbfbd..856d69d7eb86d 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -799,6 +799,11 @@
                         "Do no snippet completions for callables."
                     ]
                 },
+                "rust-analyzer.completion.fullFunctionSignatures.enable": {
+                    "markdownDescription": "Whether to show full function/method signatures in completion docs.",
+                    "default": false,
+                    "type": "boolean"
+                },
                 "rust-analyzer.completion.limit": {
                     "markdownDescription": "Maximum number of completions to return. If `None`, the limit is infinite.",
                     "default": null,