lib.fileset.gitTracked: Better error in pure eval

lib/fileset/default.nix

@@ -52,6 +52,7 @@ let
   inherit (lib.trivial)
     isFunction
     pipe
+    inPureEvalMode
     ;
 
 in {
@@ -628,7 +629,9 @@ in {
     let
       fetchResult = builtins.fetchGit path;
     in
-    if ! isPath path then
+    if inPureEvalMode then
+      throw "lib.fileset.gitTracked: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292."
+    else if ! isPath path then
       throw "lib.fileset.gitTracked: Expected the argument to be a path, but it's a ${typeOf path} instead."
     else if ! pathExists (path + "/.git") then
       throw "lib.fileset.gitTracked: Expected the argument (${toString path}) to point to a local working tree of a Git repository, but it's not."
@@ -690,7 +693,9 @@ in {
         ${if recurseSubmodules then "submodules" else null} = true;
       };
     in
-    if ! isBool recurseSubmodules then
+    if inPureEvalMode then
+      throw "lib.fileset.gitTrackedWith: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292."
+    else if ! isBool recurseSubmodules then
       throw "lib.fileset.gitTrackedWith: Expected the attribute `recurseSubmodules` of the first argument to be a boolean, but it's a ${typeOf recurseSubmodules} instead."
     else if recurseSubmodules && versionOlder nixVersion _fetchGitSubmodulesMinver then
       throw "lib.fileset.gitTrackedWith: Setting the attribute `recurseSubmodules` to `true` is only supported for Nix version ${_fetchGitSubmodulesMinver} and after, but Nix version ${nixVersion} is used."

lib/fileset/tests.sh

@@ -43,15 +43,29 @@ crudeUnquoteJSON() {
     cut -d \" -f2
 }
 
-prefixExpression='let
+prefixExpression() {
-  lib = import <nixpkgs/lib>;
+    echo 'let
-  internal = import <nixpkgs/lib/fileset/internal.nix> {
+      lib =
-    inherit lib;
+        (import <nixpkgs/lib>)
-  };
+    '
-in
+    if [[ "${1:-}" == "--simulate-pure-eval" ]]; then
-with lib;
+        echo '
-with internal;
+        .extend (final: prev: {
-with lib.fileset;'
+          trivial = prev.trivial // {
+            inPureEvalMode = true;
+          };
+        })'
+    fi
+    echo '
+      ;
+      internal = import <nixpkgs/lib/fileset/internal.nix> {
+        inherit lib;
+      };
+    in
+    with lib;
+    with internal;
+    with lib.fileset;'
+}
 
 # Check that two nix expression successfully evaluate to the same value.
 # The expressions have `lib.fileset` in scope.
@@ -60,7 +74,7 @@ expectEqual() {
     local actualExpr=$1
     local expectedExpr=$2
     if actualResult=$(nix-instantiate --eval --strict --show-trace 2>"$tmp"/actualStderr \
-        --expr "$prefixExpression ($actualExpr)"); then
+        --expr "$(prefixExpression) ($actualExpr)"); then
         actualExitCode=$?
     else
         actualExitCode=$?
@@ -68,7 +82,7 @@ expectEqual() {
     actualStderr=$(< "$tmp"/actualStderr)
 
     if expectedResult=$(nix-instantiate --eval --strict --show-trace 2>"$tmp"/expectedStderr \
-        --expr "$prefixExpression ($expectedExpr)"); then
+        --expr "$(prefixExpression) ($expectedExpr)"); then
         expectedExitCode=$?
     else
         expectedExitCode=$?
@@ -96,7 +110,7 @@ expectEqual() {
 expectStorePath() {
     local expr=$1
     if ! result=$(nix-instantiate --eval --strict --json --read-write-mode --show-trace 2>"$tmp"/stderr \
-        --expr "$prefixExpression ($expr)"); then
+        --expr "$(prefixExpression) ($expr)"); then
         cat "$tmp/stderr" >&2
         die "$expr failed to evaluate, but it was expected to succeed"
     fi
@@ -109,10 +123,16 @@ expectStorePath() {
 # The expression has `lib.fileset` in scope.
 # Usage: expectFailure NIX REGEX
 expectFailure() {
+    if [[ "$1" == "--simulate-pure-eval" ]]; then
+        maybePure="--simulate-pure-eval"
+        shift
+    else
+        maybePure=""
+    fi
     local expr=$1
     local expectedErrorRegex=$2
     if result=$(nix-instantiate --eval --strict --read-write-mode --show-trace 2>"$tmp/stderr" \
-        --expr "$prefixExpression $expr"); then
+        --expr "$(prefixExpression $maybePure) $expr"); then
         die "$expr evaluated successfully to $result, but it was expected to fail"
     fi
     stderr=$(<"$tmp/stderr")
@@ -129,12 +149,12 @@ expectTrace() {
     local expectedTrace=$2
 
     nix-instantiate --eval --show-trace >/dev/null 2>"$tmp"/stderrTrace \
-        --expr "$prefixExpression trace ($expr)" || true
+        --expr "$(prefixExpression) trace ($expr)" || true
 
     actualTrace=$(sed -n 's/^trace: //p' "$tmp/stderrTrace")
 
     nix-instantiate --eval --show-trace >/dev/null 2>"$tmp"/stderrTraceVal \
-        --expr "$prefixExpression traceVal ($expr)" || true
+        --expr "$(prefixExpression) traceVal ($expr)" || true
 
     actualTraceVal=$(sed -n 's/^trace: //p' "$tmp/stderrTraceVal")
 
@@ -1266,7 +1286,7 @@ expectFailure 'gitTrackedWith {} ./.' 'lib.fileset.gitTrackedWith: Expected the
 expectFailure 'gitTrackedWith { recurseSubmodules = null; } ./.' 'lib.fileset.gitTrackedWith: Expected the attribute `recurseSubmodules` of the first argument to be a boolean, but it'\''s a null instead.'
 
 # recurseSubmodules = true is not supported on all Nix versions
-if [[ "$(nix-instantiate --eval --expr "$prefixExpression (versionAtLeast builtins.nixVersion _fetchGitSubmodulesMinver)")" == true ]]; then
+if [[ "$(nix-instantiate --eval --expr "$(prefixExpression) (versionAtLeast builtins.nixVersion _fetchGitSubmodulesMinver)")" == true ]]; then
     fetchGitSupportsSubmodules=1
 else
     fetchGitSupportsSubmodules=
@@ -1336,6 +1356,12 @@ createGitRepo() {
     git -C "$1" commit -q --allow-empty -m "Empty commit"
 }
 
+# Check the error message for pure eval mode
+createGitRepo .
+expectFailure --simulate-pure-eval 'toSource { root = ./.; fileset = gitTracked ./.; }' 'lib.fileset.gitTracked: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292.'
+expectFailure --simulate-pure-eval 'toSource { root = ./.; fileset = gitTrackedWith {} ./.; }' 'lib.fileset.gitTrackedWith: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292.'
+rm -rf -- *
+
 # Go through all stages of Git files
 # See https://www.git-scm.com/book/en/v2/Git-Basics-Recording-Changes-to-the-Repository