SourceAccessor: Change the main interface from lstat() to maybeLstat()

src/libexpr/primops.cc

@@ -1548,10 +1548,8 @@ static void prim_pathExists(EvalState & state, const PosIdx pos, Value * * args,
 
     try {
         auto checked = state.checkSourcePath(path);
-        auto exists = checked.pathExists();
-        if (exists && mustBeDir) {
-            exists = checked.lstat().type == InputAccessor::tDirectory;
-        }
+        auto st = checked.maybeLstat();
+        auto exists = st && (!mustBeDir || st->type == SourceAccessor::tDirectory);
         v.mkBool(exists);
     } catch (SysError & e) {
         /* Don't give away info from errors while canonicalising

src/libfetchers/fs-input-accessor.cc

@@ -36,11 +36,11 @@ struct FSInputAccessorImpl : FSInputAccessor, PosixSourceAccessor
         return isAllowed(absPath) && PosixSourceAccessor::pathExists(absPath);
     }
 
-    Stat lstat(const CanonPath & path) override
+    std::optional<Stat> maybeLstat(const CanonPath & path) override
     {
         auto absPath = makeAbsPath(path);
         checkAllowed(absPath);
-        return PosixSourceAccessor::lstat(absPath);
+        return PosixSourceAccessor::maybeLstat(absPath);
     }
 
     DirEntries readDirectory(const CanonPath & path) override

src/libfetchers/memory-input-accessor.cc

@@ -20,12 +20,12 @@ struct MemoryInputAccessorImpl : MemoryInputAccessor
         return i != files.end();
     }
 
-    Stat lstat(const CanonPath & path) override
+    std::optional<Stat> maybeLstat(const CanonPath & path) override
     {
         auto i = files.find(path);
         if (i != files.end())
             return Stat { .type = tRegular, .isExecutable = false };
-        throw Error("file '%s' does not exist", path);
+        return std::nullopt;
     }
 
     DirEntries readDirectory(const CanonPath & path) override

src/libutil/posix-source-accessor.cc

@@ -44,9 +44,13 @@ bool PosixSourceAccessor::pathExists(const CanonPath & path)
     return nix::pathExists(path.abs());
 }
 
-SourceAccessor::Stat PosixSourceAccessor::lstat(const CanonPath & path)
+std::optional<SourceAccessor::Stat> PosixSourceAccessor::maybeLstat(const CanonPath & path)
 {
-    auto st = nix::lstat(path.abs());
+    struct stat st;
+    if (::lstat(path.c_str(), &st)) {
+        if (errno == ENOENT) return std::nullopt;
+        throw SysError("getting status of '%s'", showPath(path));
+    }
     mtime = std::max(mtime, st.st_mtime);
     return Stat {
         .type =

src/libutil/posix-source-accessor.hh

@@ -22,7 +22,7 @@ struct PosixSourceAccessor : SourceAccessor
 
     bool pathExists(const CanonPath & path) override;
 
-    Stat lstat(const CanonPath & path) override;
+    std::optional<Stat> maybeLstat(const CanonPath & path) override;
 
     DirEntries readDirectory(const CanonPath & path) override;
 

src/libutil/source-accessor.cc

@@ -42,12 +42,12 @@ Hash SourceAccessor::hashPath(
     return sink.finish().first;
 }
 
-std::optional<SourceAccessor::Stat> SourceAccessor::maybeLstat(const CanonPath & path)
+SourceAccessor::Stat SourceAccessor::lstat(const CanonPath & path)
 {
-    // FIXME: merge these into one operation.
-    if (!pathExists(path))
-        return {};
-    return lstat(path);
+    if (auto st = maybeLstat(path))
+        return *st;
+    else
+        throw Error("path '%s' does not exist", showPath(path));
 }
 
 std::string SourceAccessor::showPath(const CanonPath & path)

src/libutil/source-accessor.hh

@@ -61,9 +61,9 @@ struct SourceAccessor
         bool isExecutable = false; // regular files only
     };
 
-    virtual Stat lstat(const CanonPath & path) = 0;
+    Stat lstat(const CanonPath & path);
 
-    std::optional<Stat> maybeLstat(const CanonPath & path);
+    virtual std::optional<Stat> maybeLstat(const CanonPath & path) = 0;
 
     typedef std::optional<Type> DirEntry;
 

tests/functional/lang/eval-fail-bad-string-interpolation-2.err.exp

@@ -1 +1 @@
-error: getting status of '/pwd/lang/fnord': No such file or directory
+error: path '/pwd/lang/fnord' does not exist

tests/functional/lang/eval-fail-nonexist-path.err.exp

@@ -1 +1 @@
-error: getting status of '/pwd/lang/fnord': No such file or directory
+error: path '/pwd/lang/fnord' does not exist