Rollup merge of rust-lang#74286 - PankajChaudhary5:E0688, r=GuillaumeGomez

Added detailed error code explanation for issue E0688 in Rust compiler.

Added proper error explanation for issue E0688 in the Rust compiler.
Error Code E0688

Sub Part of Issue rust-lang#61137

r? @GuillaumeGomez

Author: Manishearth

src/librustc_error_codes/error_codes.rs

@@ -383,6 +383,7 @@ E0669: include_str!("./error_codes/E0669.md"),
 E0670: include_str!("./error_codes/E0670.md"),
 E0671: include_str!("./error_codes/E0671.md"),
 E0687: include_str!("./error_codes/E0687.md"),
+E0688: include_str!("./error_codes/E0688.md"),
 E0689: include_str!("./error_codes/E0689.md"),
 E0690: include_str!("./error_codes/E0690.md"),
 E0691: include_str!("./error_codes/E0691.md"),
@@ -616,7 +617,6 @@ E0768: include_str!("./error_codes/E0768.md"),
     E0640, // infer outlives requirements
 //  E0645, // trait aliases not finished
     E0667, // `impl Trait` in projections
-    E0688, // in-band lifetimes cannot be mixed with explicit lifetime binders
 //  E0694, // an unknown tool name found in scoped attributes
 //  E0702, // replaced with a generic attribute input check
 //  E0707, // multiple elided lifetimes used in arguments of `async fn`

src/librustc_error_codes/error_codes/E0688.md

@@ -0,0 +1,36 @@
+In-band lifetimes were mixed with explicit lifetime binders.
+
+Erroneous code example:
+
+```compile_fail,E0688
+#![feature(in_band_lifetimes)]
+
+fn foo<'a>(x: &'a u32, y: &'b u32) {}   // error!
+
+struct Foo<'a> { x: &'a u32 }
+
+impl Foo<'a> {
+    fn bar<'b>(x: &'a u32, y: &'b u32, z: &'c u32) {}   // error!
+}
+
+impl<'b> Foo<'a> {  // error!
+    fn baz() {}
+}
+```
+
+In-band lifetimes cannot be mixed with explicit lifetime binders.
+For example:
+
+```
+fn foo<'a, 'b>(x: &'a u32, y: &'b u32) {}   // ok!
+
+struct Foo<'a> { x: &'a u32 }
+
+impl<'a> Foo<'a> {
+    fn bar<'b,'c>(x: &'a u32, y: &'b u32, z: &'c u32) {}    // ok!
+}
+
+impl<'a> Foo<'a> {  // ok!
+    fn baz() {}
+}
+```

src/test/ui/in-band-lifetimes/E0688.stderr

@@ -24,3 +24,4 @@ LL | impl<'b> Foo<'a> {
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0688`.