docs: add long-form error-code docs for E0460

Author: Ezrashaw

compiler/rustc_error_codes/src/error_codes.rs

@@ -241,6 +241,7 @@ E0454: include_str!("./error_codes/E0454.md"),
 E0455: include_str!("./error_codes/E0455.md"),
 E0458: include_str!("./error_codes/E0458.md"),
 E0459: include_str!("./error_codes/E0459.md"),
+E0460: include_str!("./error_codes/E0460.md"),
 E0463: include_str!("./error_codes/E0463.md"),
 E0464: include_str!("./error_codes/E0464.md"),
 E0466: include_str!("./error_codes/E0466.md"),
@@ -593,7 +594,6 @@ E0791: include_str!("./error_codes/E0791.md"),
 //  E0427, // merged into 530
 //  E0456, // plugin `..` is not available for triple `..`
     E0457, // plugin `..` only found in rlib format, but must be available...
-    E0460, // found possibly newer version of crate `..`
     E0461, // couldn't find crate `..` with expected target triple ..
     E0462, // found staticlib `..` instead of rlib or dylib
     E0465, // multiple .. candidates for `..` found

compiler/rustc_error_codes/src/error_codes/E0460.md

@@ -0,0 +1,71 @@
+Found possibly newer version of crate `..` which `..` depends on.
+
+Consider these erroneous files:
+
+`a1.rs`
+```ignore (needs-linkage-with-other-tests)
+#![crate_name = "a"]
+
+pub fn foo<T>() {}
+```
+
+`a2.rs`
+```ignore (needs-linkage-with-other-tests)
+#![crate_name = "a"]
+
+pub fn foo<T>() {
+    println!("foo<T>()");
+}
+```
+
+`b.rs`
+```ignore (needs-linkage-with-other-tests)
+#![crate_name = "b"]
+
+extern crate a; // linked with `a1.rs`
+
+pub fn foo() {
+    a::foo::<isize>();
+}
+```
+
+`main.rs`
+```ignore (needs-linkage-with-other-tests)
+extern crate a; // linked with `a2.rs`
+extern crate b; // error: found possibly newer version of crate `a` which `b`
+                //        depends on
+
+fn main() {}
+```
+
+The dependency graph of this program can be represented as follows:
+```text
+    crate `main`
+         |
+         +-------------+
+         |             |
+         |             v
+depends: |         crate `b`
+ `a` v1  |             |
+         |             | depends:
+         |             |  `a` v2
+         v             |
+      crate `a` <------+
+```
+
+Crate `main` depends on crate `a` (version 1) and crate `b` which in turn
+depends on crate `a` (version 2); this discrepancy in versions cannot be
+reconciled. This difference in versions typically occurs when one crate is
+compiled and linked, then updated and linked to another crate. The crate
+"version" is a SVH (Strict Version Hash) of the crate in an
+implementation-specific way. Note that this error can *only* occur when
+directly compiling and linking with `rustc`; [Cargo] automatically resolves
+dependencies, without using the compiler's own dependency management that
+causes this issue.
+
+This error can be fixed by:
+* Using [Cargo], the Rust package manager, automatically fixing this issue.
+* Recompiling crate `a` so that both crate `b` and `main` have a uniform
+version to depend on.
+
+[Cargo]: ../cargo/index.html

src/test/ui/svh/changing-crates.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-change-lit.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-change-significant-cfg.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-change-trait-bound.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-change-type-arg.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-change-type-ret.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-change-type-static.stderr

@@ -11,3 +11,4 @@ LL | extern crate b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.

src/test/ui/svh/svh-use-trait.stderr

@@ -11,3 +11,4 @@ LL | extern crate utb;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0460`.