Add --flags=tracing, and document it in README.md

README.md

@@ -21,6 +21,21 @@ $ cabal test
 $ LANGUAGE_TESTS=yes NIXPKGS_TESTS=yes cabal test
 $ ./dist/build/hnix/hnix --help
 ```
+## Building with full debug info
+
+To build `hnix` for debugging, and with full tracing output and stack traces,
+use:
+
+```
+$ nix-shell --arg doProfiling true
+$ cabal configure --enable-tests --enable-profiling --flags=tracing
+$ cabal build
+$ ./dist/build/hnix/hnix -v5 <args> +RTS -xc
+```
+
+Note that this will run quite slowly, but will give the most information as to
+what might potentially be going wrong during parsing or evaluation.
+
 ## Building with benchmarks enabled
 
 To build `hnix` with benchmarks enabled:
@@ -32,7 +47,6 @@ $ cabal build
 $ cabal bench
 ```
 
-
 ## Building with profiling enabled
 
 To build `hnix` with profiling enabled:

hnix.cabal

@@ -2,7 +2,7 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 7880788afb8b7755b22c9bd91a3c47598fe26b9a643b2bb55816331ae179aa50
+-- hash: c030de7d44eabbd21ae044bd9108da5b34d7e3feaf8a8facbc9383c85e382186
 
 name:           hnix
 version:        0.5.0
@@ -25,6 +25,11 @@ source-repository head
   type: git
   location: https://github.com/jwiegley/hnix
 
+flag tracing
+  description: Enable full debug tracing
+  manual: True
+  default: False
+
 library
   exposed-modules:
       Nix
@@ -103,6 +108,8 @@ library
     , unordered-containers >=0.2.9 && <0.3
     , vector
     , xml
+  if flag(tracing)
+    cpp-options: -DENABLE_TRACING=1
   default-language: Haskell2010
 
 executable hnix
@@ -133,6 +140,8 @@ executable hnix
     , text
     , transformers
     , unordered-containers >=0.2.9 && <0.3
+  if flag(tracing)
+    cpp-options: -DENABLE_TRACING=1
   default-language: Haskell2010
 
 test-suite hnix-tests
@@ -175,6 +184,8 @@ test-suite hnix-tests
     , transformers
     , unix
     , unordered-containers >=0.2.9 && <0.3
+  if flag(tracing)
+    cpp-options: -DENABLE_TRACING=1
   default-language: Haskell2010
 
 benchmark hnix-benchmarks
@@ -205,4 +216,6 @@ benchmark hnix-benchmarks
     , text
     , transformers
     , unordered-containers >=0.2.9 && <0.3
+  if flag(tracing)
+    cpp-options: -DENABLE_TRACING=1
   default-language: Haskell2010

package.yaml

@@ -36,6 +36,16 @@ ghc-options:
   # - -fexpose-all-unfoldings
   # - -O2
 
+flags:
+  tracing:
+    description: Enable full debug tracing
+    manual: True
+    default: False
+
+when:
+  - condition: flag(tracing)
+    cpp-options: -DENABLE_TRACING=1
+
 library:
   source-dirs: src
   dependencies:

src/Nix/Pretty.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE OverloadedStrings #-}
@@ -25,7 +26,11 @@ import           Nix.Parser.Library (reservedNames)
 import           Nix.Parser.Operators
 import           Nix.StringOperations
 import           Nix.Thunk
+#if ENABLE_TRACING
+import           Nix.Utils
+#else
 import           Nix.Utils hiding ((<$>))
+#endif
 import           Nix.Value
 import           Prelude hiding ((<$>))
 import           Text.PrettyPrint.ANSI.Leijen

src/Nix/Thunk.hs

@@ -55,7 +55,7 @@ valueRef = Value
 buildThunk :: MonadVar m => m v -> m (Thunk m v)
 buildThunk action =
 #if ENABLE_TRACING
-    let !x = unsafePerformIO (atomicModifyIORef' counter (\x -> (succ x, x))) in
+    let !x = unsafePerformIO (atomicModifyIORef' counter (\c -> (succ c, c))) in
     Thunk x
 #else
     Thunk