Backport SourcePath from the lazy-trees branch

This introduces the SourcePath type from lazy-trees as an abstraction
for accessing files from inputs that may not be materialized in the
real filesystem (e.g. Git repositories). Currently, however, it's just
a wrapper around CanonPath, so it shouldn't change any behaviour. (On
lazy-trees, SourcePath is a <InputAccessor, CanonPath> tuple.)

src/libcmd/common-eval-args.cc

@@ -153,7 +153,7 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
     for (auto & i : autoArgs) {
         auto v = state.allocValue();
         if (i.second[0] == 'E')
-            state.mkThunk_(*v, state.parseExprFromString(i.second.substr(1), absPath(".")));
+            state.mkThunk_(*v, state.parseExprFromString(i.second.substr(1), state.rootPath(CanonPath::fromCwd())));
         else
             v->mkString(((std::string_view) i.second).substr(1));
         res.insert(state.symbols.create(i.first), v);
@@ -161,19 +161,19 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
     return res.finish();
 }
 
-Path lookupFileArg(EvalState & state, std::string_view s)
+SourcePath lookupFileArg(EvalState & state, std::string_view s)
 {
     if (EvalSettings::isPseudoUrl(s)) {
         auto storePath = fetchers::downloadTarball(
             state.store, EvalSettings::resolvePseudoUrl(s), "source", false).first.storePath;
-        return state.store->toRealPath(storePath);
+        return state.rootPath(CanonPath(state.store->toRealPath(storePath)));
     }
 
     else if (hasPrefix(s, "flake:")) {
         experimentalFeatureSettings.require(Xp::Flakes);
         auto flakeRef = parseFlakeRef(std::string(s.substr(6)), {}, true, false);
         auto storePath = flakeRef.resolve(state.store).fetchTree(state.store).first.storePath;
-        return state.store->toRealPath(storePath);
+        return state.rootPath(CanonPath(state.store->toRealPath(storePath)));
     }
 
     else if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
@@ -182,7 +182,7 @@ Path lookupFileArg(EvalState & state, std::string_view s)
     }
 
     else
-        return absPath(std::string(s));
+        return state.rootPath(CanonPath::fromCwd(s));
 }
 
 }

src/libcmd/common-eval-args.hh

@@ -8,6 +8,7 @@ namespace nix {
 class Store;
 class EvalState;
 class Bindings;
+struct SourcePath;
 
 struct MixEvalArgs : virtual Args
 {
@@ -25,6 +26,6 @@ private:
     std::map<std::string, std::string> autoArgs;
 };
 
-Path lookupFileArg(EvalState & state, std::string_view s);
+SourcePath lookupFileArg(EvalState & state, std::string_view s);
 
 }

src/libcmd/editor-for.cc

@@ -3,8 +3,11 @@
 
 namespace nix {
 
-Strings editorFor(const Path & file, uint32_t line)
+Strings editorFor(const SourcePath & file, uint32_t line)
 {
+    auto path = file.getPhysicalPath();
+    if (!path)
+        throw Error("cannot open '%s' in an editor because it has no physical path", file);
     auto editor = getEnv("EDITOR").value_or("cat");
     auto args = tokenizeString<Strings>(editor);
     if (line > 0 && (
@@ -13,7 +16,7 @@ Strings editorFor(const Path & file, uint32_t line)
         editor.find("vim") != std::string::npos ||
         editor.find("kak") != std::string::npos))
         args.push_back(fmt("+%d", line));
-    args.push_back(file);
+    args.push_back(path->abs());
     return args;
 }
 

src/libcmd/editor-for.hh

@@ -2,11 +2,12 @@
 ///@file
 
 #include "types.hh"
+#include "input-accessor.hh"
 
 namespace nix {
 
 /* Helper function to generate args that invoke $EDITOR on
    filename:lineno. */
-Strings editorFor(const Path & file, uint32_t line);
+Strings editorFor(const SourcePath & file, uint32_t line);
 
 }

src/libcmd/installable-flake.cc

@@ -96,8 +96,7 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
         auto v = attr->forceValue();
 
         if (v.type() == nPath) {
-            PathSet context;
-            auto storePath = state->copyPathToStore(context, Path(v.path));
+            auto storePath = v.path().fetchToStore(state->store);
             return {{
                 .path = DerivedPath::Opaque {
                     .path = std::move(storePath),

src/libcmd/installables.cc

@@ -427,7 +427,7 @@ Installables SourceExprCommand::parseInstallables(
         else if (file)
             state->evalFile(lookupFileArg(*state, *file), *vFile);
         else {
-            auto e = state->parseExprFromString(*expr, absPath("."));
+            auto e = state->parseExprFromString(*expr, state->rootPath(CanonPath::fromCwd()));
             state->eval(e, *vFile);
         }
 

src/libcmd/repl.cc

@@ -54,8 +54,6 @@ struct NixRepl
     , gc
     #endif
 {
-    std::string curDir;
-
     size_t debugTraceIndex;
 
     Strings loadedFiles;
@@ -113,7 +111,6 @@ NixRepl::NixRepl(const Strings & searchPath, nix::ref<Store> store, ref<EvalStat
     , staticEnv(new StaticEnv(false, state->staticBaseEnv.get()))
     , historyFile(getDataDir() + "/nix/repl-history")
 {
-    curDir = absPath(".");
 }
 
 
@@ -590,7 +587,7 @@ bool NixRepl::processLine(std::string line)
         Value v;
         evalString(arg, v);
 
-        const auto [path, line] = [&] () -> std::pair<Path, uint32_t> {
+        const auto [path, line] = [&] () -> std::pair<SourcePath, uint32_t> {
             if (v.type() == nPath || v.type() == nString) {
                 PathSet context;
                 auto path = state->coerceToPath(noPos, v, context, "while evaluating the filename to edit");
@@ -598,7 +595,7 @@ bool NixRepl::processLine(std::string line)
             } else if (v.isLambda()) {
                 auto pos = state->positions[v.lambda.fun->pos];
                 if (auto path = std::get_if<Path>(&pos.origin))
-                    return {*path, pos.line};
+                    return {SourcePath(CanonPath(*path)), pos.line};
                 else
                     throw Error("'%s' cannot be shown in an editor", pos);
             } else {
@@ -872,8 +869,7 @@ void NixRepl::addVarToScope(const Symbol name, Value & v)
 
 Expr * NixRepl::parseString(std::string s)
 {
-    Expr * e = state->parseExprFromString(std::move(s), curDir, staticEnv);
-    return e;
+    return state->parseExprFromString(std::move(s), state->rootPath(CanonPath::fromCwd()), staticEnv);
 }
 
 
@@ -930,7 +926,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
         break;
 
     case nPath:
-        str << ANSI_GREEN << v.path << ANSI_NORMAL; // !!! escaping?
+        str << ANSI_GREEN << v.path().to_string() << ANSI_NORMAL; // !!! escaping?
         break;
 
     case nNull: