Restore setting of write bits on Install'd files

SCons had undocumented behavior that Install and InstallVersionedLib
unconditionally changed the files they copied to writable - shutil.copy2(),
the underlying function used for copying, preserves mode bits.
Restore this behavior so Install won't fail in a project where it had
previously run, if any of the sources were read-only.

Fixes #3927

Signed-off-by: Mats Wichmann <mats@linux.com>

4 files changed, 65 insertions, 27 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index c259c77..e3ed2c4 100755
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -74,6 +74,7 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
     - Don't strip spaces in INSTALLSTR by using raw subst (issue 2018)
     - Deprecate Python 3.5 as a supported version.
     - CPPDEFINES now expands construction variable references (issue 2363)
+    - Restore behavior that Install()'d files are writable (issue 3927)
 
   From Dillan Mills:
     - Add support for the (TARGET,SOURCE,TARGETS,SOURCES,CHANGED_TARGETS,CHANGED_SOURCES}.relpath property.
diff --git a/RELEASE.txt b/RELEASE.txt
index fe4d82f..db64ee8 100755
--- a/RELEASE.txt
+++ b/RELEASE.txt
@@ -59,6 +59,9 @@ FIXES
     - DocbookXslt tool: The XSLT stylesheet file is now initialized to an env.File() Node, 
       such that dependencies work correctly in hierarchical builds (eg when using 
       DocbookXslt in SConscript('subdir/SConscript') context.
+    - The Install builder will now set the writable mode on the file(s) it
+      copies. This restores the (previously undocumented) SCons behavior
+      that regressed as of 4.0.0.
 
 
 IMPROVEMENTS
diff --git a/SCons/Tool/install.py b/SCons/Tool/install.py
index d73d678..9910264 100644
--- a/SCons/Tool/install.py
+++ b/SCons/Tool/install.py
@@ -31,6 +31,7 @@ selection method.
 #
 
 import os
+import stat
 from shutil import copy2, copymode, copystat
 
 import SCons.Action
@@ -152,11 +153,14 @@ def scons_copytree(src, dst, symlinks=False, ignore=None, copy_function=copy2,
 #
 # Functions doing the actual work of the Install Builder.
 #
-def copyFunc(dest, source, env):
-    """Install a source file or directory into a destination by copying,
+def copyFunc(dest, source, env) -> int:
+    """Install a source file or directory into a destination by copying.
 
-    Mode/permissions bits will be copied as well.
+    Mode/permissions bits will be copied as well, except that the target
+    will be made writable.
 
+    Returns:
+        POSIX-style error code - 0 for success, non-zero for fail
     """
     if os.path.isdir(source):
         if os.path.exists(dest):
@@ -169,19 +173,24 @@ def copyFunc(dest, source, env):
         scons_copytree(source, dest, dirs_exist_ok=True)
     else:
         copy2(source, dest)
-        copymode(source, dest)
+        st = os.stat(source)
+        os.chmod(dest, stat.S_IMODE(st[stat.ST_MODE]) | stat.S_IWRITE)
 
     return 0
 
 #
 # Functions doing the actual work of the InstallVersionedLib Builder.
 #
-def copyFuncVersionedLib(dest, source, env):
-    """Install a versioned library into a destination by copying,
+def copyFuncVersionedLib(dest, source, env) -> int:
+    """Install a versioned library into a destination by copying.
 
-    Mode/permissions bits will be copied as well.
     Any required symbolic links for other library names are created.
 
+    Mode/permissions bits will be copied as well, except that the target
+    will be made writable.
+
+    Returns:
+        POSIX-style error code - 0 for success, non-zero for fail
     """
     if os.path.isdir(source):
         raise SCons.Errors.UserError("cannot install directory `%s' as a version library" % str(source) )
@@ -192,7 +201,8 @@ def copyFuncVersionedLib(dest, source, env):
         except:
             pass
         copy2(source, dest)
-        copymode(source, dest)
+        st = os.stat(source)
+        os.chmod(dest, stat.S_IMODE(st[stat.ST_MODE]) | stat.S_IWRITE)
         installShlibLinks(dest, source, env)
 
     return 0
@@ -223,38 +233,58 @@ def installShlibLinks(dest, source, env):
         CreateLibSymlinks(env, symlinks)
     return
 
-def installFunc(target, source, env):
-    """Install a source file into a target using the function specified
-    as the INSTALL construction variable."""
+def installFunc(target, source, env) -> int:
+    """Install a source file into a target.
+
+    Uses the function specified in the INSTALL construction variable.
+
+    Returns:
+        POSIX-style error code - 0 for success, non-zero for fail
+    """
+
     try:
         install = env['INSTALL']
     except KeyError:
         raise SCons.Errors.UserError('Missing INSTALL construction variable.')
 
-    assert len(target)==len(source), \
-           "Installing source %s into target %s: target and source lists must have same length."%(list(map(str, source)), list(map(str, target)))
-    for t,s in zip(target,source):
-        if install(t.get_path(),s.get_path(),env):
+    assert len(target) == len(source), (
+        "Installing source %s into target %s: "
+        "target and source lists must have same length."
+        % (list(map(str, source)), list(map(str, target)))
+    )
+    for t, s in zip(target, source):
+        if install(t.get_path(), s.get_path(), env):
             return 1
 
     return 0
 
-def installFuncVersionedLib(target, source, env):
-    """Install a versioned library into a target using the function specified
-    as the INSTALLVERSIONEDLIB construction variable."""
+def installFuncVersionedLib(target, source, env) -> int:
+    """Install a versioned library into a target.
+
+    Uses the function specified in the INSTALL construction variable.
+
+    Returns:
+        POSIX-style error code - 0 for success, non-zero for fail
+    """
+
     try:
         install = env['INSTALLVERSIONEDLIB']
     except KeyError:
-        raise SCons.Errors.UserError('Missing INSTALLVERSIONEDLIB construction variable.')
-
-    assert len(target)==len(source), \
-           "Installing source %s into target %s: target and source lists must have same length."%(list(map(str, source)), list(map(str, target)))
-    for t,s in zip(target,source):
+        raise SCons.Errors.UserError(
+            'Missing INSTALLVERSIONEDLIB construction variable.'
+        )
+
+    assert len(target) == len(source), (
+        "Installing source %s into target %s: "
+        "target and source lists must have same length."
+        % (list(map(str, source)), list(map(str, target)))
+    )
+    for t, s in zip(target, source):
         if hasattr(t.attributes, 'shlibname'):
             tpath = os.path.join(t.get_dir(), t.attributes.shlibname)
         else:
             tpath = t.get_path()
-        if install(tpath,s.get_path(),env):
+        if install(tpath, s.get_path(), env):
             return 1
 
     return 0
@@ -461,12 +491,12 @@ def generate(env):
     try:
         env['INSTALL']
     except KeyError:
-        env['INSTALL']    = copyFunc
+        env['INSTALL'] = copyFunc
 
     try:
         env['INSTALLVERSIONEDLIB']
     except KeyError:
-        env['INSTALLVERSIONEDLIB']    = copyFuncVersionedLib
+        env['INSTALLVERSIONEDLIB'] = copyFuncVersionedLib
 
 def exists(env):
     return 1
diff --git a/SCons/Tool/install.xml b/SCons/Tool/install.xml
index f4295a0..81e486f 100644
--- a/SCons/Tool/install.xml
+++ b/SCons/Tool/install.xml
@@ -46,7 +46,9 @@ which must be a directory.
 The names of the specified source files or directories
 remain the same within the destination directory. The
 sources may be given as a string or as a node returned by
-a builder.
+a builder. Basic metadata from the source files is
+preserved, except that the target files will be marked
+as writable.
 </para>
 
 <example_commands>
@@ -118,6 +120,8 @@ See the note under &Install;.
 <para>
 Installs a versioned shared library. The symlinks appropriate to the
 architecture will be generated based on symlinks of the source library.
+Basic metadata from the source library is preserved,
+except that the target file will be marked as writable.
 </para>
 
 <example_commands>