Auto merge of rust-lang#105763 - Ezrashaw:rustc-book-relative-links, r=jyn514

Use relative links in the unstable and rustc book

Fixes rust-lang#98227.

As it stands, potential issues could arise from mismatch of stable/ nightly in the books. This PR fixes this issue by using relative links instead of absolute ones. I have replaced every absolute link under `src/doc/rustc` and `src/doc/unstable-book/` and tested each manually.

The link at `src/doc/rustc/src/targets/index.md:7`:
`[here](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_target/spec/struct.Target.html).`
I need help with because my local directory structure and https://doc.rust-lang.org/ seem to be different, where is `nightly-rustc`?

`@jyn514`

Author: bors

src/doc/rustc/src/exploit-mitigations.md

@@ -217,7 +217,7 @@ It is recommended that explicit wrapping methods such as `wrapping_add` be
 used when wrapping semantics are intended, and that explicit checking and
 wrapping methods always be used when using Unsafe Rust.
 
-<small id="fn:2">2\. See <https://doc.rust-lang.org/std/primitive.u32.html>
+<small id="fn:2">2\. See [the `u32` docs](../std/primitive.u32.html)
 for more information on the checked, overflowing, saturating, and wrapping
 methods (using u32 as an example). <a href="#fnref:2"
 class="reversefootnote" role="doc-backlink">↩</a></small>
@@ -575,17 +575,17 @@ defaults (unrelated to `READ_IMPLIES_EXEC`).
    <https://hacks.mozilla.org/2019/02/fearless-security-thread-safety/>.
 
 3. S. Klabnik and C. Nichols. “What Is Ownership?.” The Rust Programming
-   Language. <https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html>.
+   Language. [https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html](../book/ch04-01-what-is-ownership.html).
 
 4. S. Klabnik and C. Nichols. “References and Borrowing.” The Rust
    Programming Language.
-   <https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html>.
+   [https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html](../book/ch04-02-references-and-borrowing.html).
 
 5. S. Klabnik and C. Nichols. “The Slice Type.” The Rust Programming
-   Language. <https://doc.rust-lang.org/book/ch04-03-slices.html>.
+   Language. [https://doc.rust-lang.org/book/ch04-03-slices.html](../book/ch04-03-slices.html).
 
 6. S. Klabnik and C. Nichols. “Unsafe Rust.” The Rust Programming Language.
-   <https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html>.
+   [https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html](../book/ch19-01-unsafe-rust.html).
 
 7. S. Davidoff. “How Rust’s standard library was vulnerable for years and
    nobody noticed.” Medium.
@@ -696,4 +696,4 @@ defaults (unrelated to `READ_IMPLIES_EXEC`).
     for Rust #89653.” GitHub. <https://github.com/rust-lang/rust/issues/89653>.
 
 41. “ControlFlowIntegrity.” The Rust Unstable Book.
-    <https://doc.rust-lang.org/beta/unstable-book/compiler-flags/sanitizer.html#controlflowintegrity>.
+    [https://doc.rust-lang.org/unstable-book/compiler-flags/sanitizer.html#controlflowintegrity](../unstable-book/compiler-flags/sanitizer.html#controlflowintegrity).

src/doc/rustc/src/linker-plugin-lto.md

@@ -112,7 +112,7 @@ targeting Windows-like targets
 This is fixed if you explicitly set the target, for example
 `cargo build --target x86_64-pc-windows-msvc`
 Without an explicit --target the flags will be passed to all compiler invocations (including build
-scripts and proc macros), see [cargo docs on rustflags](https://doc.rust-lang.org/cargo/reference/config.html#buildrustflags)
+scripts and proc macros), see [cargo docs on rustflags](../cargo/reference/config.html#buildrustflags)
 
 If you have dependencies using the `cc` crate, you will need to set these
 environment variables:

src/doc/rustc/src/platform-support/android.md

@@ -42,4 +42,4 @@ edition of the [Android NDK].  Supported Android targets are:
 [Android NDK]: https://developer.android.com/ndk/downloads
 
 A list of all supported targets can be found
-[here](https://doc.rust-lang.org/rustc/platform-support.html)
+[here](../platform-support.html)

src/doc/rustc/src/platform-support/armv6k-nintendo-3ds.md

@@ -111,7 +111,7 @@ to an SD card to be inserted in the device.
 The `cargo-3ds` tool mentioned in [Building Rust programs](#building-rust-programs)
 supports the use of `3dslink` with `cargo 3ds run`. The default Rust test runner
 is not supported, but
-[custom test frameworks](https://doc.rust-lang.org/beta/unstable-book/language-features/custom-test-frameworks.html)
+[custom test frameworks](../../unstable-book/language-features/custom-test-frameworks.html)
 can be used with `cargo 3ds test` to run unit tests on a device.
 
 The Rust test suite for `library/std` is not yet supported.

src/doc/rustc/src/platform-support/fuchsia.md

@@ -90,7 +90,7 @@ rustup target add aarch64-fuchsia
 After installing our Fuchsia targets, we can now compile a Rust binary that targets
 Fuchsia.
 
-To create our Rust project, we can issue a standard `cargo` command as follows:
+To create our Rust project, we can use [`cargo`][cargo] as follows:
 
 **From base working directory**
 ```sh
@@ -867,7 +867,7 @@ ${SDK_PATH}/tools/${ARCH}/ffx debug connect -- \
 [Fuchsia]: https://fuchsia.dev/
 [source tree]: https://fuchsia.dev/fuchsia-src/get-started/learn/build
 [rustup]: https://rustup.rs/
-[cargo]: https://doc.rust-lang.org/cargo/
+[cargo]: ../../cargo/index.html
 [Fuchsia SDK]: https://chrome-infra-packages.appspot.com/p/fuchsia/sdk/core
 [overview of CML]: https://fuchsia.dev/fuchsia-src/concepts/components/v2/component_manifests
 [reference for the file format]: https://fuchsia.dev/reference/cml

src/doc/rustc/src/targets/custom.md

@@ -14,4 +14,4 @@ To see it for a different target, add the `--target` flag:
 rustc +nightly -Z unstable-options --target=wasm32-unknown-unknown --print target-spec-json
 ```
 
-To use a custom target, see the (unstable) [`build-std` feature](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std) of `cargo`.
+To use a custom target, see the (unstable) [`build-std` feature](../../cargo/reference/unstable.html#build-std) of `cargo`.

src/doc/unstable-book/src/compiler-flags/branch-protection.md

@@ -15,4 +15,4 @@ For example, `-Z branch-protection=bti,pac-ret,leaf` is valid, but
 
 Rust's standard library does not ship with BTI or pointer authentication enabled by default.
 In Cargo projects the standard library can be recompiled with pointer authentication using the nightly
-[build-std](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std) feature.
+[build-std](../../cargo/reference/unstable.html#build-std) feature.

src/doc/unstable-book/src/compiler-flags/control-flow-guard.md

@@ -39,7 +39,7 @@ It is strongly recommended to also enable CFG checks for all linked libraries, i
 
 To enable CFG in the standard library, use the [cargo `-Z build-std` functionality][build-std] to recompile the standard library with the same configuration options as the main program.
 
-[build-std]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std
+[build-std]: ../../cargo/reference/unstable.html#build-std
 
 For example:
 ```cmd

src/doc/unstable-book/src/compiler-flags/sanitizer.md

@@ -420,8 +420,8 @@ flow using an indirect branch/call to a function with different return and
 parameter types than the return type expected and arguments intended/passed in
 the call/branch site, the execution is also terminated (see Fig. 9).
 
-[rust-book-ch19-05]: https://doc.rust-lang.org/book/ch19-05-advanced-functions-and-closures.html
-[rust-book]: https://doc.rust-lang.org/book/title-page.html
+[rust-book-ch19-05]: ../../book/ch19-05-advanced-functions-and-closures.html
+[rust-book]: ../../book/title-page.html
 
 # HWAddressSanitizer
 
@@ -691,7 +691,7 @@ It is strongly recommended to combine sanitizers with recompiled and
 instrumented standard library, for example using [cargo `-Zbuild-std`
 functionality][build-std].
 
-[build-std]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std
+[build-std]: ../../cargo/reference/unstable.html#build-std
 
 # Build scripts and procedural macros
 

src/doc/unstable-book/src/compiler-flags/virtual-function-elimination.md

@@ -36,4 +36,4 @@ optimized out, if unused. However, with `make_foo` you can produce a wrapped
 to inlining of `f`, `Foo::foo` can then be called from a foreign crate. This can
 lead to miscompilations.
 
-[Clto]: https://doc.rust-lang.org/rustc/codegen-options/index.html#lto
+[Clto]: ../../rustc/codegen-options/index.html#lto