doc: use lang-specific base-builder images (#6415)

docs/getting-started/new-project-guide/go_lang.md

@@ -59,6 +59,8 @@ sanitizers:
 
 ### Dockerfile
 
+The Dockerfile should start by `FROM gcr.io/oss-fuzz-base/base-builder-go`
+
 The OSS-Fuzz builder image has the latest stable release of Golang installed. In
 order to install dependencies of your project, add `RUN git clone ...` command to
 your Dockerfile.

docs/getting-started/new-project-guide/jvm_lang.md

@@ -63,6 +63,8 @@ sanitizers:
 
 ### Dockerfile
 
+The Dockerfile should start by `FROM gcr.io/oss-fuzz-base/base-builder-jvm`
+
 The OSS-Fuzz base Docker images already come with OpenJDK 15 pre-installed. If
 you need Maven to build your project, you can install it by adding the following
 line to your Dockerfile:

docs/getting-started/new-project-guide/python_lang.md

@@ -57,6 +57,8 @@ sanitizers:
 
 ### Dockerfile
 
+The Dockerfile should start by `FROM gcr.io/oss-fuzz-base/base-builder-python`
+
 Because most dependencies are already pre-installed on the images, no
 significant changes are needed in the Dockerfile for Python fuzzing projects.
 You should simply clone the project, set a `WORKDIR`, and copy any necessary

docs/getting-started/new-project-guide/rust_lang.md

@@ -61,6 +61,8 @@ fuzzing_engines:
 
 ### Dockerfile
 
+The Dockerfile should start by `FROM gcr.io/oss-fuzz-base/base-builder-rust`
+
 The OSS-Fuzz builder image has the latest nightly release of Rust as well as
 `cargo fuzz` pre-installed and in `PATH`. In the `Dockerfile` for your project
 all you'll need to do is fetch the latest copy of your code and install any

docs/getting-started/new_project_guide.md

@@ -99,6 +99,7 @@ Programming language the project is written in. Values you can specify include:
 * [`rust`]({{ site.baseurl }}//getting-started/new-project-guide/rust-lang/)
 * [`python`]({{ site.baseurl }}//getting-started/new-project-guide/python-lang/)
 * [`jvm` (Java, Kotlin, Scala and other JVM-based languages)]({{ site.baseurl }}//getting-started/new-project-guide/jvm-lang/)
+* [`swift`]({{ site.baseurl }}//getting-started/new-project-guide/swift/)
 
 ### primary_contact, auto_ccs {#primary}
 The primary contact and list of other contacts to be CCed. Each person listed gets access to ClusterFuzz, including crash reports and fuzzer statistics, and are auto-cced on new bugs filed in the OSS-Fuzz
@@ -208,11 +209,21 @@ COPY build.sh fuzzer.cc $SRC/                # copy build script and other fuzze
 ```
 In the above example, the git clone will check out the source to `$SRC/<checkout_dir>`.
 
+Depending on your project's language, you will use a different base image,
+for instance `FROM gcr.io/oss-fuzz-base/base-builder-go` for golang.
+
 For an example, see
 [expat/Dockerfile](https://github.com/google/oss-fuzz/tree/master/projects/expat/Dockerfile)
 or
 [syzkaller/Dockerfile](https://github.com/google/oss-fuzz/blob/master/projects/syzkaller/Dockerfile).
 
+In the case of a project with multiple languages/toolchains needed,
+you can run installation scripts `install_lang.sh` where lang is the language needed.
+You also need to setup environment variables needed by this toolchain, for example `GOPATH` is needed by golang.
+For an example, see
+[ecc-diff-fuzzer/Dockerfile](https://github.com/google/oss-fuzz/blob/master/projects/ecc-diff-fuzzer/Dockerfile).
+where we use `base-builder-rust`and install golang
+
 ## build.sh {#buildsh}
 
 This file defines how to build binaries for [fuzz targets]({{ site.baseurl }}/reference/glossary/#fuzz-target) in your project.