From 99a491caeb2ecce5e746966f15d84d8a7a288bef Mon Sep 17 00:00:00 2001
From: helly25 <marcus.boerger@gmail.com>
Date: Sat, 8 Nov 2025 18:42:24 +0100
Subject: [PATCH 1/3] Explain how version/requirement ccan be used from env
 vars.

---
 README.md | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/README.md b/README.md
index c0e55246..a3f7a7c8 100644
--- a/README.md
+++ b/README.md
@@ -142,6 +142,34 @@ supporting `<`, `<=`, `>`, `>=`, `==`, `!=`. Examples:
 - `latest:>17.0.4,!=19.1.7,<=20.1.0`
 - `first:>=15.0.6,<16`
 
+It is further possible to provide the version or requirement from an environment
+variable with a fallback version or requirement. In this case it is important to
+also use the bazel flag `--repo_env=LLVM_VERSION=version_or_requirement`. It is
+important to use both correctly because otherwise the resulting builds are not
+reproducible. The main purpose of using an environment variable to encode the
+version is for integration or batch testing on multiple platforms where multiple
+LLVM version should be tested.
+
+- `getenv(ENVIRONMENT_VARIABLE_NAME,fallback)`
+
+Example `MODULE.bazel`
+
+```
+llvm.toolchain(
+    name = "llvm_toolchain",
+    llvm_versions = {
+        "": "getenv(LLVM_VERSION,latest:>=17.0.0,<20)",
+        "darwin-x86_64": "15.0.7",  # Verify this works as opposed to using one version.
+    },
+)
+```
+
+In this example, MacOS x86 machines have their LLVM version hard-coded to
+`15.0.7`. For all other targets the LLVM version is read from the environment
+variable `LLVM_VERSION` which must be referenced on the Bazel command line as
+explained above. If the variabel is not present, then the LLVM version defaults
+to the requirement expression `latest:>=17.0.0,<20`.
+
 ### Selecting Toolchains
 
 If toolchains are registered (see Quickstart section above), you do not need to

From 21b85a3138683448e2cc46f6262f4cf44dccbff4 Mon Sep 17 00:00:00 2001
From: helly25 <marcus.boerger@gmail.com>
Date: Sat, 8 Nov 2025 18:44:48 +0100
Subject: [PATCH 2/3] Make trunk check happy.

---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index a3f7a7c8..0f17811a 100644
--- a/README.md
+++ b/README.md
@@ -154,7 +154,7 @@ LLVM version should be tested.
 
 Example `MODULE.bazel`
 
-```
+```starlark
 llvm.toolchain(
     name = "llvm_toolchain",
     llvm_versions = {

From 161171e619a2048d9d9d4cf403e746041ce0f4a5 Mon Sep 17 00:00:00 2001
From: helly25 <marcus.boerger@gmail.com>
Date: Sat, 8 Nov 2025 18:51:59 +0100
Subject: [PATCH 3/3] Apply suggestions

---
 README.md | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 0f17811a..3e84becf 100644
--- a/README.md
+++ b/README.md
@@ -147,8 +147,8 @@ variable with a fallback version or requirement. In this case it is important to
 also use the bazel flag `--repo_env=LLVM_VERSION=version_or_requirement`. It is
 important to use both correctly because otherwise the resulting builds are not
 reproducible. The main purpose of using an environment variable to encode the
-version is for integration or batch testing on multiple platforms where multiple
-LLVM version should be tested.
+version for integration or batch testing on multiple platforms where multiple
+LLVM versions should be tested.
 
 - `getenv(ENVIRONMENT_VARIABLE_NAME,fallback)`
 
@@ -167,7 +167,7 @@ llvm.toolchain(
 In this example, MacOS x86 machines have their LLVM version hard-coded to
 `15.0.7`. For all other targets the LLVM version is read from the environment
 variable `LLVM_VERSION` which must be referenced on the Bazel command line as
-explained above. If the variabel is not present, then the LLVM version defaults
+explained above. If the variable is not present, then the LLVM version defaults
 to the requirement expression `latest:>=17.0.0,<20`.
 
 ### Selecting Toolchains