Merge pull request NixOS#5416 from bburdette/debug-exploratory-PR

--debugger flag
pedromfedricci · May 26, 2022 · 5f097fb · 5f097fb
2 parents d8398d3 + 9068d32
commit 5f097fb
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Showing 17 changed files with 906 additions and 310 deletions.
diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
@@ -25,5 +25,18 @@
   Selecting derivation outputs using the attribute selection syntax
   (e.g. `nixpkgs#glibc.dev`) no longer works.
 
+* Running nix with the new `--debugger` flag will cause it to start a repl session if
+  there is an exception thrown during eval, or if `builtins.break` is called.  From
+  there one can inspect symbol values and evaluate nix expressions.  In debug mode
+  the following new repl commands are available:
+  ```
+  :env          Show env stack
+  :bt           Show trace stack
+  :st           Show current trace
+  :st <idx>     Change to another trace in the stack
+  :c            Go until end of program, exception, or builtins.break().
+  :s            Go one step
+  ```
+
 * `builtins.fetchTree` (and flake inputs) can now be used to fetch plain files
   over the `http(s)` and `file` protocols in addition to directory tarballs.
diff --git a/src/libcmd/command.cc b/src/libcmd/command.cc
@@ -86,6 +86,11 @@ ref<Store> CopyCommand::getDstStore()
 
 EvalCommand::EvalCommand()
 {
+    addFlag({
+        .longName = "debugger",
+        .description = "start an interactive environment if evaluation fails",
+        .handler = {&startReplOnEvalErrors, true},
+    });
 }
 
 EvalCommand::~EvalCommand()
@@ -103,7 +108,7 @@ ref<Store> EvalCommand::getEvalStore()
 
 ref<EvalState> EvalCommand::getEvalState()
 {
-    if (!evalState)
+    if (!evalState) {
         evalState =
             #if HAVE_BOEHMGC
             std::allocate_shared<EvalState>(traceable_allocator<EvalState>(),
@@ -113,6 +118,11 @@ ref<EvalState> EvalCommand::getEvalState()
                 searchPath, getEvalStore(), getStore())
             #endif
             ;
+
+        if (startReplOnEvalErrors) {
+            evalState->debugRepl = &runRepl;        
+        };
+    }
     return ref<EvalState>(evalState);
 }
 

diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
@@ -57,6 +57,8 @@ struct CopyCommand : virtual StoreCommand
 
 struct EvalCommand : virtual StoreCommand, MixEvalArgs
 {
+    bool startReplOnEvalErrors = false;
+
     EvalCommand();
 
     ~EvalCommand();
@@ -270,4 +272,8 @@ void printClosureDiff(
     const StorePath & afterPath,
     std::string_view indent);
 
+
+void runRepl(
+    ref<EvalState> evalState,
+    const ValMap & extraEnv);
 }
diff --git a/src/libcmd/local.mk b/src/libcmd/local.mk
@@ -6,9 +6,9 @@ libcmd_DIR := $(d)
 
 libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
-libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers
+libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers -I src/nix
 
-libcmd_LDFLAGS += $(LOWDOWN_LIBS) -pthread
+libcmd_LDFLAGS = $(EDITLINE_LIBS) -llowdown -pthread
 
 libcmd_LIBS = libstore libutil libexpr libmain libfetchers