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Add more suggestions on converting Makefile conditionals

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Change-Id: I5ccf5824c6a85d881070d8e0ae16d87d3ee6cee2
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Colin Cross
2019-11-12 14:39:17 -08:00
parent 409e833def
commit 2322c4dc9b
2 changed files with 159 additions and 10 deletions
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README.md
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@@ -303,12 +303,19 @@ written to a [ninja](http://ninja-build.org) build file.
### How do I write conditionals?
Soong deliberately does not support conditionals in Android.bp files.
Instead, complexity in build rules that would require conditionals are handled
in Go, where high level language features can be used and implicit dependencies
introduced by conditionals can be tracked. Most conditionals are converted
to a map property, where one of the values in the map will be selected and
appended to the top level properties.
Soong deliberately does not support conditionals in Android.bp files. We
suggest removing most conditionals from the build. See
[Best Practices](docs/best_practices.md#removing-conditionals) for some
examples on how to remove conditionals.
In cases where build time conditionals are unavoidable, complexity in build
rules that would require conditionals are handled in Go through Soong plugins.
This allows Go language features to be used for better readability and
testability, and implicit dependencies introduced by conditionals can be
tracked. Most conditionals supported natively by Soong are converted to a map
property. When building the module one of the properties in the map will be
selected, and its values appended to the property with the same name at the
top level of the module.
For example, to support architecture specific files:
```
@@ -326,9 +333,9 @@ cc_library {
}
```
See [art/build/art.go](https://android.googlesource.com/platform/art/+/master/build/art.go)
or [external/llvm/soong/llvm.go](https://android.googlesource.com/platform/external/llvm/+/master/soong/llvm.go)
for examples of more complex conditionals on product variables or environment variables.
When building the module for arm the `generic.cpp` and `arm.cpp` sources will
be built. When building for x86 the `generic.cpp` and 'x86.cpp' sources will
be built.
## Developing for Soong
@@ -346,7 +353,7 @@ the IDE.
To run the soong_build process in a debugger, install `dlv` and then start the build with
`SOONG_DELVE=<listen addr>` in the environment.
For examle:
For example:
```bash
SOONG_DELVE=:1234 m nothing
```