Remove reference to Rust gcda coverage (since it's now removed) (#1403)

Fixes #1240

Author: nb-ccd

README.md

@@ -19,7 +19,6 @@ This is a project initiated by Mozilla to gather code coverage results on Firefo
 - [Usage](#usage)
   - [Example: How to generate source-based coverage for a Rust project](#example-how-to-generate-source-based-coverage-for-a-rust-project)
   - [Example: How to generate .gcda files for C/C++](#example-how-to-generate-gcda-files-for-cc)
-  - [Example: How to generate .gcda files for a Rust project](#example-how-to-generate-gcda-files-for-a-rust-project)
   - [Generate a coverage report from coverage artifacts](#generate-a-coverage-report-from-coverage-artifacts)
     - [LCOV output](#lcov-output)
     - [Coveralls output](#coveralls-output)
@@ -223,37 +222,12 @@ you can run `cargo install grcov`.
 
 In the CWD, you will see a `.profraw` file has been generated. This contains the profiling information that grcov will parse, alongside with your binaries.
 
+Note that gcov coverage using the `-Zprofile` flag is no longer supported in Rust (details [here](https://github.com/rust-lang/rust/pull/131829)). Use source based coverage and the `-Cinstrument-coverage` flag instead.
+
 ### Example: How to generate .gcda files for C/C++
 
 Pass `--coverage` to `clang` or `gcc` (or for older gcc versions pass `-ftest-coverage` and `-fprofile-arcs` options (see [gcc docs](https://gcc.gnu.org/onlinedocs/gcc/Gcov-Data-Files.html)).
 
-### Example: How to generate .gcda files for a Rust project
-
-**Nightly Rust is required** to use grcov for Rust gcov-based coverage. Alternatively, you can `export
-RUSTC_BOOTSTRAP=1`, which basically turns your stable rustc into a Nightly one.
-
-1. Ensure that the following environment variables are set up:
-
-   ```sh
-   export CARGO_INCREMENTAL=0
-   export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
-   export RUSTDOCFLAGS="-Cpanic=abort"
-   ```
-
-   These will ensure that things like dead code elimination do not skew the coverage.
-
-2. Build your code:
-
-   `cargo build`
-
-   If you look in `target/debug/deps` dir you will see `.gcno` files have appeared. These are the locations that could be covered.
-
-3. Run your tests:
-
-   `cargo test`
-
-   In the `target/debug/deps/` dir you will now also see `.gcda` files. These contain the hit counts on which of those locations have been reached. Both sets of files are used as inputs to `grcov`.
-
 ### Generate a coverage report from coverage artifacts
 
 Generate a html coverage report like this:
@@ -310,31 +284,6 @@ script:
     - bash <(curl -s https://codecov.io/bash) -f lcov.info
 ```
 
-Here is an example of .travis.yml file:
-
-```yaml
-language: rust
-
-before_install:
-  - curl -L https://github.com/mozilla/grcov/releases/latest/download/grcov-x86_64-unknown-linux-gnu.tar.bz2 | tar jxf -
-
-matrix:
-  include:
-    - os: linux
-      rust: stable
-
-script:
-    - export CARGO_INCREMENTAL=0
-    - export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
-    - export RUSTDOCFLAGS="-Cpanic=abort"
-    - cargo build --verbose $CARGO_OPTIONS
-    - cargo test --verbose $CARGO_OPTIONS
-    - |
-      zip -0 ccov.zip `find . \( -name "YOUR_PROJECT_NAME*.gc*" \) -print`;
-      ./grcov ccov.zip -s . -t lcov --llvm --branch --ignore-not-existing --ignore "/*" -o lcov.info;
-      bash <(curl -s https://codecov.io/bash) -f lcov.info;
-```
-
 #### grcov with Gitlab
 
 Here is an example `.gitlab-ci.yml` which will build your project, then collect coverage data in a format that Gitlab understands. It is assumed that you'll use an image which already has relevant tools installed, if that's not the case put the appropriate commands at the beginning of the `script` stanza.