From 5d68300a21cc8ae4245c1813f0efc0c7d090f674 Mon Sep 17 00:00:00 2001
From: Robin <randersson@anaconda.com>
Date: Tue, 28 Apr 2026 09:32:43 -0400
Subject: [PATCH 1/6] Improve error handling of long paths for EXE installers

---
 constructor/fcp.py             | 15 +++++---
 constructor/nsis/main.nsi.tmpl | 32 +++++++++++++++-
 constructor/winexe.py          |  1 +
 tests/test_fcp.py              | 68 +++++++++++++++++++++++++++++++++-
 4 files changed, 109 insertions(+), 7 deletions(-)

diff --git a/constructor/fcp.py b/constructor/fcp.py
index 4ad7f53ca..f2ce24667 100644
--- a/constructor/fcp.py
+++ b/constructor/fcp.py
@@ -153,6 +153,7 @@ def check_duplicates_files(pc_recs, platform, duplicate_files="error"):
     # Keep a min, 50MB buffer size
     total_tarball_size = 52428800
     total_extracted_pkgs_size = 52428800
+    max_relative_path_length = 0
 
     for pc_rec in pc_recs:
         fn = pc_rec.fn
@@ -163,6 +164,7 @@ def check_duplicates_files(pc_recs, platform, duplicate_files="error"):
         paths_data = read_paths_json(extracted_package_dir).paths
         for path_data in paths_data:
             short_path = path_data.path
+            max_relative_path_length = max(max_relative_path_length, len(short_path))
             try:
                 size = path_data.size_in_bytes or getsize(join(extracted_package_dir, short_path))
             except AttributeError:
@@ -176,7 +178,7 @@ def check_duplicates_files(pc_recs, platform, duplicate_files="error"):
             map_members_icase[short_path_lower]["fns"].add(fn)
 
     if duplicate_files == "skip":
-        return total_tarball_size, total_extracted_pkgs_size
+        return total_tarball_size, total_extracted_pkgs_size, max_relative_path_length
 
     logger.info("Checking for duplicate files ...")
     for member in map_members_scase:
@@ -201,7 +203,7 @@ def check_duplicates_files(pc_recs, platform, duplicate_files="error"):
             else:
                 sys.exit(f"Error: {msg_str}")
 
-    return total_tarball_size, total_extracted_pkgs_size
+    return total_tarball_size, total_extracted_pkgs_size, max_relative_path_length
 
 
 def _precs_from_environment(environment, input_dir):
@@ -443,7 +445,7 @@ def _main(
             input_dir=input_dir,
         )
     if dry_run:
-        return None, None, None, None, None, None, None, None
+        return None, None, None, None, None, None, None, None, None
     pc_recs, _urls, dists, has_conda = _fetch_precs(
         precs, download_dir, transmute_file_type=transmute_file_type
     )
@@ -463,8 +465,8 @@ def _main(
         duplicate_files = "skip"
 
     all_pc_recs = list({rec: None for rec in all_pc_recs})  # deduplicate
-    approx_tarballs_size, approx_pkgs_size = check_duplicates_files(
-        pc_recs, platform, duplicate_files=duplicate_files
+    approx_tarballs_size, approx_pkgs_size, max_relative_path_length = check_duplicates_files(
+        all_pc_recs, platform, duplicate_files=duplicate_files
     )
 
     return (
@@ -476,6 +478,7 @@ def _main(
         approx_pkgs_size,
         has_conda,
         extra_envs_data,
+        max_relative_path_length,
     )
 
 
@@ -529,6 +532,7 @@ def main(info, verbose=True, dry_run=False, conda_exe="conda.exe"):
             approx_pkgs_size,
             has_conda,
             extra_envs_info,
+            max_relative_path_length,
         ) = _main(
             name,
             version,
@@ -561,3 +565,4 @@ def main(info, verbose=True, dry_run=False, conda_exe="conda.exe"):
     info["_has_conda"] = has_conda
     # contains {env_name: [_dists, _urls, _records]} for each extra environment
     info["_extra_envs_info"] = extra_envs_info
+    info["_max_relative_path_length"] = max_relative_path_length
diff --git a/constructor/nsis/main.nsi.tmpl b/constructor/nsis/main.nsi.tmpl
index 10bf6c9f4..197a087d4 100644
--- a/constructor/nsis/main.nsi.tmpl
+++ b/constructor/nsis/main.nsi.tmpl
@@ -130,6 +130,7 @@ ${Using:StrFunc} StrStr
 # are not written into install.log. STEP_LOG creates an intermittent file
 # that is output into these streams after the commands finish.
 !define STEP_LOG                      "$INSTDIR\.step.log"
+!define MAX_RELATIVE_PATH_LENGTH {{ max_relative_path_length }}
 
 var /global INIT_CONDA
 var /global REG_PY
@@ -168,6 +169,7 @@ var /global IsDomainUser
 var /global CheckPathLength
 var /global LongPathsEnabled
 var /global InstDirLen
+var /global PathTooLongHint
 
 var /global InstModePage_RadioButton_JustMe
 var /global InstModePage_RadioButton_AllUsers
@@ -1115,6 +1117,25 @@ Function OnDirectoryLeave
         ${EndIf}
     ${EndIf}
 
+    # MAX_PATH check - runs independently of check_path_length
+    ${If} $LongPathsEnabled == "0"
+        IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
+        ${If} $0 > 260
+            ${If} ${Silent}
+                ${Print} "::warning:: The installation path may be too long ($0 chars, limit 260). Some files could fail to extract."
+            ${Else}
+                MessageBox MB_YESNO|MB_ICONWARNING \
+                    "The installation path may be too long. Some files could fail to extract.$\n$\n\
+                     Maximum file path: $0 characters (limit: 260).$\n$\n\
+                     You can either choose a shorter path or enable Long Paths in Windows.$\n$\n\
+                     Continue anyway?" \
+                    IDYES continue_long_path
+                Abort
+                continue_long_path:
+            ${EndIf}
+        ${EndIf}
+    ${EndIf}
+
     # Call the CheckForSpaces function.
     Push $INSTDIR # Input string (install path).
     Call CheckForSpaces
@@ -1586,9 +1607,18 @@ Section "Install"
     File {{ dist }}
 {%- endfor %}
 
+    # Set hint for extraction error if path may be too long
+    IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
+    ${If} $0 > 260
+    ${AndIf} $LongPathsEnabled == "0"
+        StrCpy $PathTooLongHint "$\n$\nThis may be caused by the installation path being too long."
+    ${Else}
+        StrCpy $PathTooLongHint ""
+    ${EndIf}
+
     ${Print} "Setting up the package cache..."
     push '"$INSTDIR\_conda.exe" constructor --prefix "$INSTDIR" --extract-conda-pkgs {{ CONDA_LOG_ARG }}'
-    push 'Failed to extract packages'
+    push 'Failed to extract packages$PathTooLongHint'
     push 'WithLog'
     call AbortRetryNSExecWait
 
diff --git a/constructor/winexe.py b/constructor/winexe.py
index caf49f066..add5c3bed 100644
--- a/constructor/winexe.py
+++ b/constructor/winexe.py
@@ -252,6 +252,7 @@ def make_nsi(
     variables["initialize_by_default"] = info.get("initialize_by_default", None)
     variables["check_path_length"] = info.get("check_path_length", False)
     variables["check_path_spaces"] = info.get("check_path_spaces", True)
+    variables["max_relative_path_length"] = info.get("_max_relative_path_length", 0)
     variables["keep_pkgs"] = info.get("keep_pkgs") or False
     variables["pre_install_exists"] = bool(info.get("pre_install"))
     variables["post_install_exists"] = bool(info.get("post_install"))
diff --git a/tests/test_fcp.py b/tests/test_fcp.py
index a27411580..9cce65552 100644
--- a/tests/test_fcp.py
+++ b/tests/test_fcp.py
@@ -1,10 +1,11 @@
 from __future__ import annotations
 
 from contextlib import nullcontext
+from unittest.mock import patch
 
 import pytest
 
-from constructor.fcp import check_duplicates, exclude_packages
+from constructor.fcp import check_duplicates, check_duplicates_files, exclude_packages
 
 
 class GenericObject:
@@ -64,3 +65,68 @@ def test_exclude_packages(values: tuple[..., GenericObject], expected_value):
     with context:
         packages = exclude_packages(*values)
         assert packages == expected_value
+
+
+class MockPathData:
+    """Represents a file path entry."""
+
+    def __init__(self, path):
+        self.path = path
+        self.size_in_bytes = 1  # must be non-zero to avoid filesystem access
+
+
+class MockPathsJson:
+    """Wraps a list of MockPathData entries."""
+
+    def __init__(self, paths):
+        self.paths = [MockPathData(p) for p in paths]
+
+
+class MockPackageCacheRecord:
+    """Represents a package record."""
+
+    def __init__(self, fn, extracted_package_dir, paths):
+        self.fn = fn
+        self.extracted_package_dir = extracted_package_dir
+        self._paths = paths
+
+    def get(self, key, default=None):
+        return default
+
+
+@patch("constructor.fcp.read_paths_json")
+def test_check_duplicates_files_returns_max_path_length(mock_read_paths):
+    """Verify function returns max path length as third tuple element."""
+    pc_rec1 = MockPackageCacheRecord(
+        fn="pkg1-1.0.tar.bz2",
+        extracted_package_dir="/cache/pkg1",
+        paths=["lib/short.py"],  # 12 chars
+    )
+    pc_rec2 = MockPackageCacheRecord(
+        fn="pkg2-1.0.tar.bz2",
+        extracted_package_dir="/cache/pkg2",
+        paths=["lib/python3.10/site-packages/longer.py"],  # 38 chars
+    )
+
+    def read_paths_side_effect(extracted_dir):
+        if extracted_dir == "/cache/pkg1":
+            return MockPathsJson(pc_rec1._paths)
+        return MockPathsJson(pc_rec2._paths)
+
+    mock_read_paths.side_effect = read_paths_side_effect
+
+    result = check_duplicates_files([pc_rec1, pc_rec2], "win-64", duplicate_files="skip")
+
+    assert len(result) == 3
+    _, _, max_path_len = result
+    assert max_path_len == 38
+
+
+@patch("constructor.fcp.read_paths_json")
+def test_check_duplicates_files_empty_packages(mock_read_paths):
+    """Verify returns 0 when no packages provided."""
+    result = check_duplicates_files([], "win-64", duplicate_files="skip")
+
+    assert len(result) == 3
+    assert result[2] == 0
+    mock_read_paths.assert_not_called()

From 85c1bb58b229b534d1f8179e6671ef8aabff619d Mon Sep 17 00:00:00 2001
From: Robin <randersson@anaconda.com>
Date: Tue, 28 Apr 2026 09:40:35 -0400
Subject: [PATCH 2/6] Fix format

---
 constructor/nsis/main.nsi.tmpl | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/constructor/nsis/main.nsi.tmpl b/constructor/nsis/main.nsi.tmpl
index 197a087d4..158667b9a 100644
--- a/constructor/nsis/main.nsi.tmpl
+++ b/constructor/nsis/main.nsi.tmpl
@@ -1125,10 +1125,13 @@ Function OnDirectoryLeave
                 ${Print} "::warning:: The installation path may be too long ($0 chars, limit 260). Some files could fail to extract."
             ${Else}
                 MessageBox MB_YESNO|MB_ICONWARNING \
-                    "The installation path may be too long. Some files could fail to extract.$\n$\n\
-                     Maximum file path: $0 characters (limit: 260).$\n$\n\
-                     You can either choose a shorter path or enable Long Paths in Windows.$\n$\n\
-                     Continue anyway?" \
+                    "The installation path may be too long. Some files could fail to extract.$\n\
+                    $\n\
+                    Maximum file path: $0 characters (limit: 260).$\n\
+                    $\n\
+                    You can either choose a shorter path or enable Long Paths in Windows.$\n\
+                    $\n\
+                    Continue anyway?" \
                     IDYES continue_long_path
                 Abort
                 continue_long_path:

From dbd5521a70cf7f4f591e642bac3572e1eef477b0 Mon Sep 17 00:00:00 2001
From: Robin <randersson@anaconda.com>
Date: Tue, 28 Apr 2026 09:49:15 -0400
Subject: [PATCH 3/6] Improve format

---
 constructor/nsis/main.nsi.tmpl | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/constructor/nsis/main.nsi.tmpl b/constructor/nsis/main.nsi.tmpl
index 158667b9a..d0d318800 100644
--- a/constructor/nsis/main.nsi.tmpl
+++ b/constructor/nsis/main.nsi.tmpl
@@ -1124,13 +1124,9 @@ Function OnDirectoryLeave
             ${If} ${Silent}
                 ${Print} "::warning:: The installation path may be too long ($0 chars, limit 260). Some files could fail to extract."
             ${Else}
-                MessageBox MB_YESNO|MB_ICONWARNING \
-                    "The installation path may be too long. Some files could fail to extract.$\n\
-                    $\n\
-                    Maximum file path: $0 characters (limit: 260).$\n\
-                    $\n\
-                    You can either choose a shorter path or enable Long Paths in Windows.$\n\
-                    $\n\
+                MessageBox MB_YESNO|MB_ICONEXCLAMATION \
+                    "The installation path may be too long ($0 chars, limit 260).$\n\
+                    Some files could fail to extract.$\n$\n\
                     Continue anyway?" \
                     IDYES continue_long_path
                 Abort

From ddcb0b0552f47d0b359cab87d62fbda0a273e2d3 Mon Sep 17 00:00:00 2001
From: Robin <randersson@anaconda.com>
Date: Wed, 29 Apr 2026 10:43:42 -0400
Subject: [PATCH 4/6] Fix some review comments

---
 constructor/fcp.py             | 49 +++++++++++++++++++++++++++++++---
 constructor/nsis/main.nsi.tmpl |  2 ++
 tests/requirements.txt         |  1 +
 tests/test_fcp.py              | 42 +++++++++++++++++++++++++----
 4 files changed, 85 insertions(+), 9 deletions(-)

diff --git a/constructor/fcp.py b/constructor/fcp.py
index f2ce24667..7d5488b64 100644
--- a/constructor/fcp.py
+++ b/constructor/fcp.py
@@ -13,10 +13,11 @@
 import sys
 import tempfile
 from collections import defaultdict
+from collections.abc import Iterable
 from itertools import groupby
 from os.path import abspath, expanduser, isdir, join
 from subprocess import check_call
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Literal
 
 from constructor.utils import filename_dist
 
@@ -144,8 +145,35 @@ def _fetch(download_dir, precs):
     return list(dict.fromkeys(PrefixGraph(pc.iter_records()).graph))
 
 
-def check_duplicates_files(pc_recs, platform, duplicate_files="error"):
+def check_duplicates_files(
+    pc_recs: Iterable["PackageCacheRecord"],
+    platform: str,
+    duplicate_files: Literal["error", "warn", "skip"] = "error",
+    env_prefixes: dict["PackageCacheRecord", str] | None = None,
+) -> tuple[int, int, int]:
+    """
+    Check for duplicate files across packages and compute size/path metrics.
+
+    Iterates through all files in the provided package cache records to:
+    1. Detect duplicate files (same path in multiple packages)
+    2. Compute approximate tarball and extracted sizes
+    3. Track the longest relative file path (for MAX_PATH validation on Windows)
+
+    Args:
+        pc_recs: Package cache records to check.
+        platform: Target platform string (e.g., "win-64", "linux-64").
+        duplicate_files: How to handle duplicates - "error", "warn", or "skip".
+        env_prefixes: Optional dict mapping PackageCacheRecord -> path prefix string.
+            Used to account for extra_envs paths which are installed under
+            "envs/<name>/" rather than the base install directory. Records not
+            in this dict are assumed to be in the base environment (no prefix).
+
+    Returns:
+        Tuple of (approx_tarball_size, approx_extracted_size, max_relative_path_length)
+    """
     assert duplicate_files in ("warn", "skip", "error")
+    if env_prefixes is None:
+        env_prefixes = {}
 
     map_members_scase = defaultdict(set)
     map_members_icase = defaultdict(lambda: {"files": set(), "fns": set()})
@@ -162,9 +190,12 @@ def check_duplicates_files(pc_recs, platform, duplicate_files="error"):
         total_tarball_size += int(pc_rec.get("size", 0))
 
         paths_data = read_paths_json(extracted_package_dir).paths
+        env_prefix_len = len(env_prefixes.get(pc_rec, ""))
         for path_data in paths_data:
             short_path = path_data.path
-            max_relative_path_length = max(max_relative_path_length, len(short_path))
+            max_relative_path_length = max(
+                max_relative_path_length, env_prefix_len + len(short_path)
+            )
             try:
                 size = path_data.size_in_bytes or getsize(join(extracted_package_dir, short_path))
             except AttributeError:
@@ -452,11 +483,17 @@ def _main(
     all_pc_recs = pc_recs.copy()
 
     extra_envs_data = {}
+    env_prefixes = {}  # Maps pc_rec -> "envs/<name>/" prefix for max path calculation
     for env_name, env_precs in extra_envs_precs.items():
         env_pc_recs, env_urls, env_dists, _ = _fetch_precs(
             env_precs, download_dir, transmute_file_type=transmute_file_type
         )
         extra_envs_data[env_name] = {"_urls": env_urls, "_dists": env_dists, "_records": env_precs}
+        env_prefix = f"envs/{env_name}/"
+        for pc_rec in env_pc_recs:
+            existing_prefix = env_prefixes.get(pc_rec, "")
+            if len(env_prefix) > len(existing_prefix):
+                env_prefixes[pc_rec] = env_prefix
         all_pc_recs += env_pc_recs
 
     duplicate_files = "warn" if ignore_duplicate_files else "error"
@@ -465,8 +502,12 @@ def _main(
         duplicate_files = "skip"
 
     all_pc_recs = list({rec: None for rec in all_pc_recs})  # deduplicate
+    # Pass all_pc_recs (base + extra_envs) to check_duplicates_files:
+    # - When extra_envs exists, duplicate_files="skip" so only sizes and max path are computed
+    # - When no extra_envs, all_pc_recs == pc_recs
+    # - env_prefixes dict ensures max path accounts for "envs/<name>/" prefix in extra_envs
     approx_tarballs_size, approx_pkgs_size, max_relative_path_length = check_duplicates_files(
-        all_pc_recs, platform, duplicate_files=duplicate_files
+        all_pc_recs, platform, duplicate_files=duplicate_files, env_prefixes=env_prefixes
     )
 
     return (
diff --git a/constructor/nsis/main.nsi.tmpl b/constructor/nsis/main.nsi.tmpl
index d0d318800..aca754e8c 100644
--- a/constructor/nsis/main.nsi.tmpl
+++ b/constructor/nsis/main.nsi.tmpl
@@ -1120,6 +1120,7 @@ Function OnDirectoryLeave
     # MAX_PATH check - runs independently of check_path_length
     ${If} $LongPathsEnabled == "0"
         IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
+        IntOp $0 $0 + 1  # Account for path separator between install dir and relative path
         ${If} $0 > 260
             ${If} ${Silent}
                 ${Print} "::warning:: The installation path may be too long ($0 chars, limit 260). Some files could fail to extract."
@@ -1608,6 +1609,7 @@ Section "Install"
 
     # Set hint for extraction error if path may be too long
     IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
+    IntOp $0 $0 + 1  # Account for path separator between install dir and relative path
     ${If} $0 > 260
     ${AndIf} $LongPathsEnabled == "0"
         StrCpy $PathTooLongHint "$\n$\nThis may be caused by the installation path being too long."
diff --git a/tests/requirements.txt b/tests/requirements.txt
index 7284b97cb..637b33cca 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,5 +1,6 @@
 pytest
 pytest-cov
+pytest-mock
 coverage
 jinja2
 ruamel.yaml
diff --git a/tests/test_fcp.py b/tests/test_fcp.py
index 9cce65552..40d233410 100644
--- a/tests/test_fcp.py
+++ b/tests/test_fcp.py
@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 from contextlib import nullcontext
-from unittest.mock import patch
 
 import pytest
 
@@ -94,8 +93,7 @@ def get(self, key, default=None):
         return default
 
 
-@patch("constructor.fcp.read_paths_json")
-def test_check_duplicates_files_returns_max_path_length(mock_read_paths):
+def test_check_duplicates_files_returns_max_path_length(mocker):
     """Verify function returns max path length as third tuple element."""
     pc_rec1 = MockPackageCacheRecord(
         fn="pkg1-1.0.tar.bz2",
@@ -113,6 +111,7 @@ def read_paths_side_effect(extracted_dir):
             return MockPathsJson(pc_rec1._paths)
         return MockPathsJson(pc_rec2._paths)
 
+    mock_read_paths = mocker.patch("constructor.fcp.read_paths_json")
     mock_read_paths.side_effect = read_paths_side_effect
 
     result = check_duplicates_files([pc_rec1, pc_rec2], "win-64", duplicate_files="skip")
@@ -122,11 +121,44 @@ def read_paths_side_effect(extracted_dir):
     assert max_path_len == 38
 
 
-@patch("constructor.fcp.read_paths_json")
-def test_check_duplicates_files_empty_packages(mock_read_paths):
+def test_check_duplicates_files_empty_packages(mocker):
     """Verify returns 0 when no packages provided."""
+    mock_read_paths = mocker.patch("constructor.fcp.read_paths_json")
+
     result = check_duplicates_files([], "win-64", duplicate_files="skip")
 
     assert len(result) == 3
     assert result[2] == 0
     mock_read_paths.assert_not_called()
+
+
+def test_check_duplicates_files_with_env_prefixes(mocker):
+    """Verify env_prefixes adds prefix length to max path calculation."""
+    pc_rec_base = MockPackageCacheRecord(
+        fn="base-pkg-1.0.tar.bz2",
+        extracted_package_dir="/cache/base-pkg",
+        paths=["lib/short.py"],  # 12 chars, no prefix -> 12
+    )
+    pc_rec_env = MockPackageCacheRecord(
+        fn="env-pkg-1.0.tar.bz2",
+        extracted_package_dir="/cache/env-pkg",
+        paths=["lib/short.py"],  # 12 chars, with "envs/myenv/" prefix (11) -> 23
+    )
+
+    def read_paths_side_effect(extracted_dir):
+        if extracted_dir == "/cache/base-pkg":
+            return MockPathsJson(pc_rec_base._paths)
+        return MockPathsJson(pc_rec_env._paths)
+
+    mock_read_paths = mocker.patch("constructor.fcp.read_paths_json")
+    mock_read_paths.side_effect = read_paths_side_effect
+
+    env_prefixes = {pc_rec_env: "envs/myenv/"}
+    result = check_duplicates_files(
+        [pc_rec_base, pc_rec_env], "win-64", duplicate_files="skip", env_prefixes=env_prefixes
+    )
+
+    assert len(result) == 3
+    _, _, max_path_len = result
+    # "envs/myenv/" (11) + "lib/short.py" (12) = 23
+    assert max_path_len == 23

From c66ac79a36c4390ba743f2dfa043ad4faa32239c Mon Sep 17 00:00:00 2001
From: Robin <randersson@anaconda.com>
Date: Wed, 29 Apr 2026 12:09:56 -0400
Subject: [PATCH 5/6] Review fixes, change warning into error

---
 CONSTRUCT.md                           |  8 +++----
 constructor/_schema.py                 |  8 +++----
 constructor/data/construct.schema.json |  3 ++-
 constructor/nsis/main.nsi.tmpl         | 32 +++++++++-----------------
 docs/source/construct-yaml.md          |  8 +++----
 5 files changed, 25 insertions(+), 34 deletions(-)

diff --git a/CONSTRUCT.md b/CONSTRUCT.md
index 17a71302f..a36239ab6 100644
--- a/CONSTRUCT.md
+++ b/CONSTRUCT.md
@@ -552,11 +552,11 @@ interactive installation. (Windows only).
 
 Only applies if `register_python` is true.
 
-### `check_path_length`
+### ~~`check_path_length`~~
 
-Check the length of the path where the distribution is installed to ensure nodejs
-can be installed.  Raise a message to request shorter paths (less than 46 character)
-or enable long paths on windows > 10 (require admin right). Default is False. (Windows only).
+_Deprecated_. Path length validation is now always performed using the computed
+maximum relative path length from the package contents. This option will be
+removed in a future version. (Windows only).
 
 ### `check_path_spaces`
 
diff --git a/constructor/_schema.py b/constructor/_schema.py
index 87945ad03..280fff613 100644
--- a/constructor/_schema.py
+++ b/constructor/_schema.py
@@ -721,11 +721,11 @@ class ConstructorConfiguration(BaseModel):
 
     Only applies if `register_python` is true.
     """
-    check_path_length: bool = False
+    check_path_length: bool = Field(False, deprecated=True)
     """
-    Check the length of the path where the distribution is installed to ensure nodejs
-    can be installed.  Raise a message to request shorter paths (less than 46 character)
-    or enable long paths on windows > 10 (require admin right). Default is False. (Windows only).
+    _Deprecated_. Path length validation is now always performed using the computed
+    maximum relative path length from the package contents. This option will be
+    removed in a future version. (Windows only).
     """
     check_path_spaces: bool = True
     """
diff --git a/constructor/data/construct.schema.json b/constructor/data/construct.schema.json
index f0178d738..1c72a59f4 100644
--- a/constructor/data/construct.schema.json
+++ b/constructor/data/construct.schema.json
@@ -477,7 +477,8 @@
     },
     "check_path_length": {
       "default": false,
-      "description": "Check the length of the path where the distribution is installed to ensure nodejs can be installed. Raise a message to request shorter paths (less than 46 character) or enable long paths on windows > 10 (require admin right). Default is False. (Windows only).",
+      "deprecated": true,
+      "description": "_Deprecated_. Path length validation is now always performed using the computed maximum relative path length from the package contents. This option will be removed in a future version. (Windows only).",
       "title": "Check Path Length",
       "type": "boolean"
     },
diff --git a/constructor/nsis/main.nsi.tmpl b/constructor/nsis/main.nsi.tmpl
index aca754e8c..c598e3d91 100644
--- a/constructor/nsis/main.nsi.tmpl
+++ b/constructor/nsis/main.nsi.tmpl
@@ -169,7 +169,6 @@ var /global IsDomainUser
 var /global CheckPathLength
 var /global LongPathsEnabled
 var /global InstDirLen
-var /global PathTooLongHint
 
 var /global InstModePage_RadioButton_JustMe
 var /global InstModePage_RadioButton_AllUsers
@@ -1117,22 +1116,23 @@ Function OnDirectoryLeave
         ${EndIf}
     ${EndIf}
 
-    # MAX_PATH check - runs independently of check_path_length
+    # MAX_PATH check - installation will fail if path exceeds 260 characters
     ${If} $LongPathsEnabled == "0"
         IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
         IntOp $0 $0 + 1  # Account for path separator between install dir and relative path
         ${If} $0 > 260
+            IntOp $1 260 - ${MAX_RELATIVE_PATH_LENGTH}
+            IntOp $1 $1 - 1  # Account for path separator
             ${If} ${Silent}
-                ${Print} "::warning:: The installation path may be too long ($0 chars, limit 260). Some files could fail to extract."
+                ${Print} "::error:: The installation path is too long. Your path is $InstDirLen characters, but must be at most $1 characters."
             ${Else}
-                MessageBox MB_YESNO|MB_ICONEXCLAMATION \
-                    "The installation path may be too long ($0 chars, limit 260).$\n\
-                    Some files could fail to extract.$\n$\n\
-                    Continue anyway?" \
-                    IDYES continue_long_path
-                Abort
-                continue_long_path:
+                MessageBox MB_OK|MB_ICONSTOP \
+                    "The installation path is too long.$\n$\n\
+                    Your path is $InstDirLen characters, but must be at most $1 characters.$\n$\n\
+                    Please choose a shorter installation path." \
+                    /SD IDOK
             ${EndIf}
+            Abort
         ${EndIf}
     ${EndIf}
 
@@ -1607,19 +1607,9 @@ Section "Install"
     File {{ dist }}
 {%- endfor %}
 
-    # Set hint for extraction error if path may be too long
-    IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
-    IntOp $0 $0 + 1  # Account for path separator between install dir and relative path
-    ${If} $0 > 260
-    ${AndIf} $LongPathsEnabled == "0"
-        StrCpy $PathTooLongHint "$\n$\nThis may be caused by the installation path being too long."
-    ${Else}
-        StrCpy $PathTooLongHint ""
-    ${EndIf}
-
     ${Print} "Setting up the package cache..."
     push '"$INSTDIR\_conda.exe" constructor --prefix "$INSTDIR" --extract-conda-pkgs {{ CONDA_LOG_ARG }}'
-    push 'Failed to extract packages$PathTooLongHint'
+    push 'Failed to extract packages'
     push 'WithLog'
     call AbortRetryNSExecWait
 
diff --git a/docs/source/construct-yaml.md b/docs/source/construct-yaml.md
index 17a71302f..a36239ab6 100644
--- a/docs/source/construct-yaml.md
+++ b/docs/source/construct-yaml.md
@@ -552,11 +552,11 @@ interactive installation. (Windows only).
 
 Only applies if `register_python` is true.
 
-### `check_path_length`
+### ~~`check_path_length`~~
 
-Check the length of the path where the distribution is installed to ensure nodejs
-can be installed.  Raise a message to request shorter paths (less than 46 character)
-or enable long paths on windows > 10 (require admin right). Default is False. (Windows only).
+_Deprecated_. Path length validation is now always performed using the computed
+maximum relative path length from the package contents. This option will be
+removed in a future version. (Windows only).
 
 ### `check_path_spaces`
 

From 28f600401d35a439012da18fa01fb3ca307b012e Mon Sep 17 00:00:00 2001
From: Robin <randersson@anaconda.com>
Date: Fri, 1 May 2026 11:53:10 -0400
Subject: [PATCH 6/6] Review fixes

---
 constructor/fcp.py             | 13 +++++++---
 constructor/nsis/main.nsi.tmpl | 46 ----------------------------------
 constructor/winexe.py          |  1 -
 tests/test_examples.py         |  2 +-
 4 files changed, 10 insertions(+), 52 deletions(-)

diff --git a/constructor/fcp.py b/constructor/fcp.py
index 7d5488b64..f92c36b3d 100644
--- a/constructor/fcp.py
+++ b/constructor/fcp.py
@@ -7,17 +7,18 @@
 fcp (fetch conda packages) module
 """
 
+from __future__ import annotations
+
 import logging
 import os
 import shutil
 import sys
 import tempfile
 from collections import defaultdict
-from collections.abc import Iterable
 from itertools import groupby
 from os.path import abspath, expanduser, isdir, join
 from subprocess import check_call
-from typing import TYPE_CHECKING, Literal
+from typing import TYPE_CHECKING
 
 from constructor.utils import filename_dist
 
@@ -39,6 +40,9 @@
 )
 
 if TYPE_CHECKING:
+    from collections.abc import Iterable
+    from typing import Literal
+
     from .conda_interface import PackageCacheRecord
 
 logger = logging.getLogger(__name__)
@@ -146,10 +150,10 @@ def _fetch(download_dir, precs):
 
 
 def check_duplicates_files(
-    pc_recs: Iterable["PackageCacheRecord"],
+    pc_recs: Iterable[PackageCacheRecord],
     platform: str,
     duplicate_files: Literal["error", "warn", "skip"] = "error",
-    env_prefixes: dict["PackageCacheRecord", str] | None = None,
+    env_prefixes: dict[PackageCacheRecord, str] | None = None,
 ) -> tuple[int, int, int]:
     """
     Check for duplicate files across packages and compute size/path metrics.
@@ -167,6 +171,7 @@ def check_duplicates_files(
             Used to account for extra_envs paths which are installed under
             "envs/<name>/" rather than the base install directory. Records not
             in this dict are assumed to be in the base environment (no prefix).
+            The prefix string should include the trailing slash (e.g., "envs/myenv/").
 
     Returns:
         Tuple of (approx_tarball_size, approx_extracted_size, max_relative_path_length)
diff --git a/constructor/nsis/main.nsi.tmpl b/constructor/nsis/main.nsi.tmpl
index c598e3d91..bed31f6ef 100644
--- a/constructor/nsis/main.nsi.tmpl
+++ b/constructor/nsis/main.nsi.tmpl
@@ -157,7 +157,6 @@ var /global ARGV_RegisterPython
 var /global ARGV_NoRegistry
 var /global ARGV_NoScripts
 var /global ARGV_NoShortcuts
-var /global ARGV_CheckPathLength
 var /global ARGV_QuietMode
 {%- if uninstall_with_conda_exe %}
 var /global ARGV_Uninst_RemoveConfigFiles
@@ -166,7 +165,6 @@ var /global ARGV_Uninst_RemoveCaches
 {%- endif %}
 
 var /global IsDomainUser
-var /global CheckPathLength
 var /global LongPathsEnabled
 var /global InstDirLen
 
@@ -293,7 +291,6 @@ Function SkipPageIfUACInnerInstance
 FunctionEnd
 
 Function InitializeVariables
-    StrCpy $CheckPathLength "{{ 1 if check_path_length else 0 }}"
     StrCpy $NO_REGISTRY "0"
 
     # Package cache option
@@ -366,7 +363,6 @@ FunctionEnd
                 /NoRegistry=[0|1] [default: AllUsers: 0, JustMe: 0]$\n\
                 /NoScripts=[0|1] [default: 0]$\n\
                 /NoShortcuts=[0|1] [default: 0]$\n\
-                /CheckPathLength=[0|1] [default: {{ 1 if check_path_length else 0 }}]$\n\
                 /? (show this help message)$\n\
                 /S (run in CLI/headless mode)$\n\
                 /Q (quiet mode, do not print output to console)$\n\
@@ -498,16 +494,6 @@ FunctionEnd
         StrCpy $Ana_CreateShortcuts_State ${BST_UNCHECKED}
     ${EndIf}
 
-    ClearErrors
-    ${GetOptions} $ARGV "/CheckPathLength=" $ARGV_CheckPathLength
-    ${IfNot} ${Errors}
-        ${If} $ARGV_CheckPathLength = "0"
-            StrCpy $CheckPathLength "0"
-        ${ElseIf} $ARGV_CheckPathLength = "1"
-            StrCpy $CheckPathLength "1"
-        ${EndIf}
-    ${EndIf}
-
     ClearErrors
     ${GetOptions} $ARGV "/Q" $ARGV_QuietMode
     ${IfNot} ${Errors}
@@ -1084,38 +1070,6 @@ Function OnDirectoryLeave
     ReadRegStr $LongPathsEnabled HKLM "SYSTEM\CurrentControlSet\Control\FileSystem" "LongPathsEnabled"
     StrLen $InstDirLen "$InstDir"
 
-    ${If} $CheckPathLength == "1"
-    ${AndIf} $LongPathsEnabled == "0"
-    ${AndIf} $InstDirLen > 46
-        ; With windows 10, we can enable support for long path, for earlier
-        ; version, suggest user to use shorter installation path
-        ${If} ${AtLeastWin10}
-        ${AndIfNot} $NO_REGISTRY = "1"
-            ; If we have admin right, we enable long path on windows
-            ${If} ${UAC_IsAdmin}
-                WriteRegDWORD HKLM "SYSTEM\CurrentControlSet\Control\FileSystem" "LongPathsEnabled" 1
-            ; If we don't have admin right, we suggest a shorter path or suggest to run with admin right
-            ${Else}
-                ${Print} "::error:: The installation path should be shorter than 46 characters or \
-                             the installation requires administrator rights to enable long \
-                             path on Windows."
-                MessageBox MB_OK|MB_ICONSTOP "The installation path should be shorter than 46 characters or \
-                                              the installation requires administrator rights to enable long \
-                                              path on Windows." \
-                           /SD IDOK
-                Abort
-            ${EndIf}
-        ; If we don't have admin right, we suggest a shorter path or suggest to run with admin right
-        ${Else}
-            ${Print} "::error:: The installation path should be shorter than 46 characters. \
-                         Please choose another location."
-            MessageBox MB_OK|MB_ICONSTOP "The installation path should be shorter than 46 characters. \
-                                          Please choose another location." \
-                       /SD IDOK
-            Abort
-        ${EndIf}
-    ${EndIf}
-
     # MAX_PATH check - installation will fail if path exceeds 260 characters
     ${If} $LongPathsEnabled == "0"
         IntOp $0 $InstDirLen + ${MAX_RELATIVE_PATH_LENGTH}
diff --git a/constructor/winexe.py b/constructor/winexe.py
index add5c3bed..5cd2ec522 100644
--- a/constructor/winexe.py
+++ b/constructor/winexe.py
@@ -250,7 +250,6 @@ def make_nsi(
     variables.update(ns_platform(info["_platform"]))
     variables["initialize_conda"] = info.get("initialize_conda", "classic")
     variables["initialize_by_default"] = info.get("initialize_by_default", None)
-    variables["check_path_length"] = info.get("check_path_length", False)
     variables["check_path_spaces"] = info.get("check_path_spaces", True)
     variables["max_relative_path_length"] = info.get("_max_relative_path_length", 0)
     variables["keep_pkgs"] = info.get("keep_pkgs") or False
diff --git a/tests/test_examples.py b/tests/test_examples.py
index 4ec5c9a64..71c944fcd 100644
--- a/tests/test_examples.py
+++ b/tests/test_examples.py
@@ -162,7 +162,7 @@ def _check_installer_log(install_dir):
             "Once you have installed it, set NSIS_USING_LOG_BUILD=1.\n"
             "Otherwise, this usually means that the destination folder could not be created.\n"
             "Possible causes: permissions, non-supported characters, long paths...\n"
-            "Consider setting 'check_path_spaces' and 'check_path_length' to 'False'."
+            "Consider setting 'check_path_spaces' to 'False'."
         )
     if error_lines:
         raise AssertionError("\n".join(error_lines))