https://github.com/andreabedini/cabal-syntax-json
Cabal-syntax-json
https://github.com/andreabedini/cabal-syntax-json
Last synced: about 2 months ago
JSON representation
Cabal-syntax-json
- Host: GitHub
- URL: https://github.com/andreabedini/cabal-syntax-json
- Owner: andreabedini
- Created: 2022-10-07T04:17:21.000Z (almost 3 years ago)
- Default Branch: main
- Last Pushed: 2025-04-04T10:25:40.000Z (3 months ago)
- Last Synced: 2025-05-12T23:14:29.526Z (2 months ago)
- Language: Haskell
- Size: 147 KB
- Stars: 0
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Cabal-syntax-json
This package provides a robust JSON representation of cabal files. While it is not the first
or the only package to do so, I believe it has some interesting features that make it worth:
1. Simple. Zero non-boot dependency, you only need GHC.
2. Robust. It uses Cabal-syntax own code and makes no assumptions on the fields.
3. Helpful. It transforms if conditions in a format easier to handle.
4. Flexible. It can simplify those conditionals based on flags passed on the cli.
This tool is aimed to build-system developers who need to extract information about a package to drive the build process.
## Usage
```
Usage: cabal2json [OPTION...] files...
-h --help Print this help message
--out=FILE Path for output
-f FLAG --flag=FLAG Specialise to flag assignment FLAG
-c COMPILER --compiler=COMPILER Specialise to the compiler COMPILER
-o OS --os=OS Specialise to the operating system OS
-a ARCH --arch=ARCH Specialise to the architecture ARCH
-p PLATFORM --platform=PLATFORM Specialise to the platform PLATFORM
--debug Output an intermediate format useful for debugging
--pristine Preserve the conditional structure
```
## Example
Using [template-haskell-2.19.0.0](https://hackage.haskell.org/package/template-haskell-2.19.0.0/revision/0.cabal), `cabal2json` produces:
```json
{
"cabal-version": ">=1.10",
"name": "template-haskell",
"version": "2.19.0.0",
"license": "BSD3",
"license-file": [
"LICENSE"
],
"license-files": [
"LICENSE"
],
"maintainer": "[email protected]",
"bug-reports": "https://gitlab.haskell.org/ghc/ghc/issues/new",
"synopsis": "Support library for Template Haskell",
"description": "This package provides modules containing facilities for manipulating\nHaskell source code using Template Haskell.\n\nSee for more\ninformation.",
"category": "Template Haskell",
"build-type": "Simple",
"extra-source-files": [
"changelog.md"
],
"source-repositories": {
"head": {
"type": "git",
"location": "https://gitlab.haskell.org/ghc/ghc.git",
"subdir": "libraries/template-haskell"
}
},
"components": {
"lib": {
"exposed-modules": [
"Language.Haskell.TH",
"Language.Haskell.TH.Lib",
"Language.Haskell.TH.Ppr",
"Language.Haskell.TH.PprLib",
"Language.Haskell.TH.Quote",
"Language.Haskell.TH.Syntax",
"Language.Haskell.TH.LanguageExtensions",
"Language.Haskell.TH.CodeDo",
"Language.Haskell.TH.Lib.Internal"
],
"other-modules": [
"Language.Haskell.TH.Lib.Map",
{
"_if": {
"flag": "vendor-filepath"
},
"_then": [
"System.FilePath",
"System.FilePath.Posix",
"System.FilePath.Windows"
]
}
],
"default-language": "Haskell2010",
"default-extensions": [
"NoImplicitPrelude",
{
"_if": {
"flag": "vendor-filepath"
},
"_then": [
"ImplicitPrelude"
]
}
],
"other-extensions": [
"BangPatterns",
"CPP",
"DefaultSignatures",
"DeriveDataTypeable",
"DeriveGeneric",
"FlexibleInstances",
"RankNTypes",
"RoleAnnotations",
"ScopedTypeVariables"
],
"ghc-options": [
"-Wall",
"-this-unit-id",
"template-haskell"
],
"build-depends": [
{
"package": "base",
"version": ">=4.11 && <4.18",
"libs": [
"base"
]
},
{
"package": "ghc-boot-th",
"version": "==9.4.1",
"libs": [
"ghc-boot-th"
]
},
{
"package": "ghc-prim",
"version": ">=0",
"libs": [
"ghc-prim"
]
},
{
"package": "pretty",
"version": ">=1.1 && <1.2",
"libs": [
"pretty"
]
},
{
"_if": {
"not": {
"flag": "vendor-filepath"
}
},
"_then": [
{
"package": "filepath",
"version": ">=0",
"libs": [
"filepath"
]
}
]
}
],
"hs-source-dirs": [
{
"_if": {
"flag": "vendor-filepath"
},
"_then": [
"./vendored-filepath",
"."
]
},
{
"_if": {
"not": {
"flag": "vendor-filepath"
}
},
"_then": [
"."
]
}
]
}
}
}
```
Activating the flag `vendor-filepath` with `cabal2json --flag +vendor-filepath` produces:
```json
{
"cabal-version": ">=1.10",
"name": "template-haskell",
"version": "2.19.0.0",
"license": "BSD3",
"license-file": [
"LICENSE"
],
"license-files": [
"LICENSE"
],
"maintainer": "[email protected]",
"bug-reports": "https://gitlab.haskell.org/ghc/ghc/issues/new",
"synopsis": "Support library for Template Haskell",
"description": "This package provides modules containing facilities for manipulating\nHaskell source code using Template Haskell.\n\nSee for more\ninformation.",
"category": "Template Haskell",
"build-type": "Simple",
"extra-source-files": [
"changelog.md"
],
"source-repositories": {
"head": {
"type": "git",
"location": "https://gitlab.haskell.org/ghc/ghc.git",
"subdir": "libraries/template-haskell"
}
},
"flags": {
"vendor-filepath": {
"description": "Vendor the dependency on filepath",
"default": false,
"manual": true
}
},
"components": {
"lib": {
"exposed-modules": [
"Language.Haskell.TH",
"Language.Haskell.TH.Lib",
"Language.Haskell.TH.Ppr",
"Language.Haskell.TH.PprLib",
"Language.Haskell.TH.Quote",
"Language.Haskell.TH.Syntax",
"Language.Haskell.TH.LanguageExtensions",
"Language.Haskell.TH.CodeDo",
"Language.Haskell.TH.Lib.Internal"
],
"hs-source-dirs": [
"./vendored-filepath",
"."
],
"other-modules": [
"Language.Haskell.TH.Lib.Map",
"System.FilePath",
"System.FilePath.Posix",
"System.FilePath.Windows"
],
"default-language": "Haskell2010",
"default-extensions": [
"NoImplicitPrelude",
"ImplicitPrelude"
],
"other-extensions": [
"BangPatterns",
"CPP",
"DefaultSignatures",
"DeriveDataTypeable",
"DeriveGeneric",
"FlexibleInstances",
"RankNTypes",
"RoleAnnotations",
"ScopedTypeVariables"
],
"ghc-options": [
"-Wall",
"-this-unit-id",
"template-haskell"
],
"build-depends": [
{
"package": "base",
"version": ">=4.11 && <4.18",
"libs": [
"base"
]
},
{
"package": "ghc-boot-th",
"version": "==9.4.1",
"libs": [
"ghc-boot-th"
]
},
{
"package": "ghc-prim",
"version": ">=0",
"libs": [
"ghc-prim"
]
},
{
"package": "pretty",
"version": ">=1.1 && <1.2",
"libs": [
"pretty"
]
}
]
}
}
}
```
## Details
The JSON representation is obtained through the following steps:
- A cabal file is parsed using `readGenericPackageDescription`.
- The cli flags are used to simplify the conditionals.
- The conditionals are pushed down into the field values. E.g.
```cabal
if flag(vendor-filepath)
other-modules:
System.FilePath
System.FilePath.Posix
System.FilePath.Windows
hs-source-dirs:
./vendored-filepath
.
default-extensions:
ImplicitPrelude
else
build-depends:
filepath
hs-source-dirs:
.
```
is transformed into:
```cabal
other-modules:
if flag(vendor-filepath)
System.FilePath
System.FilePath.Posix
System.FilePath.Windows
hs-source-dirs:
if flag(vendor-filepath)
./vendored-filepath
.
default-extensions:
if flag(vendor-filepath)
ImplicitPrelude
build-depends:
if !flag(vendor-filepath)
filepath
hs-source-dirs:
if !flag(vendor-filepath)
.
```
In other words, a tree of fields is transformed into fields of trees.
- Lastly the tree is flattened into a list where every field value is guarded by its cumulative conditionals.
```cabal
if impl(ghc >= 8.0)
if flag(os-string)
build-depends: filepath >= 1.5.0.0, os-string >= 2.0.0
else
build-depends: filepath >= 1.4.100.0 && < 1.5.0.0
```
becomes
```cabal
build-depends:
if impl(ghc >= 8.0) && flag(os-string)
filepath >= 1.5.0.0
os-string >= 2.0.0
if impl(ghc >= 8.0) && !flag(os-string)
filepath >= 1.4.100.0 && < 1.5.0.0
```
## Author
Andrea Bedini ([email protected])