ship versioned tbb libraries on linux again

The oneTBB cmake build only versions its output on Windows, so on Linux
RcppParallel 6.0.x installed unversioned libraries (e.g. 'libtbb.so' with
SONAME 'libtbb.so'). RcppParallel 5.1.11 and earlier shipped a real
'libtbb.so.2' plus a 'libtbb.so' redirect, inherited from Intel TBB's
make-based build (which set the SONAME from TBB_COMPATIBLE_INTERFACE_VERSION).

Binaries compiled against those releases recorded a load-time dependency on
'libtbb.so.2', and so fail to load after an upgrade with "libtbb.so.2: cannot
open shared object file". Restore the versioned layout for the bundled TBB on
Linux by renaming 'libtbb*.so' to 'libtbb*.so.2' and re-creating 'libtbb*.so'
as a symlink. A symlink (rather than a linker script) is used so the name
resolves at runtime as well as at link time.

Author: kevinushey

NEWS.md

@@ -1,5 +1,13 @@
 # RcppParallel (development version)
 
+* On Linux, the bundled TBB libraries are once again installed with versioned
+  names (e.g. `libtbb.so.2`) plus an unversioned `libtbb.so` symlink, matching
+  the layout shipped by RcppParallel 5.1.11 and earlier. The oneTBB cmake build
+  produces only unversioned libraries on Linux, so binaries compiled against
+  those releases (which recorded a load-time dependency on `libtbb.so.2`) would
+  otherwise fail to load after an upgrade with "libtbb.so.2: cannot open shared
+  object file".
+
 * Fixed installation on Windows toolchains providing an older (non-oneTBB)
   copy of TBB, e.g. Rtools42: the tbb stub library is now built by
   re-exporting the static TBB library, rather than wrapping the oneTBB

src/install.libs.R

@@ -50,6 +50,11 @@
          system2("cp", c("-P", shQuote(tbbLib), shQuote(tbbDest)))
       }
 
+      # restore the versioned library layout shipped by RcppParallel 5.1.11
+      # and earlier (a real 'libtbb.so.2' plus a 'libtbb.so' symlink)
+      if (Sys.info()[["sysname"]] == "Linux")
+         versionBundledTbbLibraries(tbbDest)
+
    } else {
 
       # using system tbb
@@ -145,6 +150,46 @@ buildTbbStub <- function(tbbDest) {
 
 }
 
+# Give the bundled TBB libraries the versioned '.so.<N>' names, plus an
+# unversioned 'libtbb.so' compatibility symlink, that RcppParallel shipped on
+# Linux through 5.1.11. That layout came from Intel TBB's make-based build,
+# which set the library SONAME from TBB_COMPATIBLE_INTERFACE_VERSION (2) and
+# emitted 'libtbb.so' as a linker script pointing at 'libtbb.so.2'. The
+# oneTBB cmake build only versions its output on Windows, so on Linux it
+# produces unversioned libraries (e.g. 'libtbb.so' with SONAME 'libtbb.so')
+# instead. Binaries compiled against RcppParallel <= 5.1.11 recorded a
+# load-time dependency on 'libtbb.so.2'; without this, they fail to load after
+# an upgrade with "libtbb.so.2: cannot open shared object file".
+versionBundledTbbLibraries <- function(tbbDest) {
+
+   # downstream binaries look for exactly '.so.2', matching the SONAME suffix
+   # the old TBB build derived from TBB_COMPATIBLE_INTERFACE_VERSION
+   suffix <- "2"
+
+   libs <- list.files(tbbDest, pattern = "^libtbb.*\\.so$", full.names = TRUE)
+   for (lib in libs) {
+
+      # leave symlinks and linker scripts (i.e. an already-versioned layout)
+      # untouched; only real, unversioned libraries need renaming
+      if (nzchar(Sys.readlink(lib)))
+         next
+
+      versioned <- paste0(lib, ".", suffix)
+      if (file.exists(versioned))
+         next
+
+      writeLines(sprintf("** versioning tbb library '%s' -> '%s'",
+                         basename(lib), basename(versioned)))
+
+      # 'libtbb.so' -> 'libtbb.so.2', then re-create 'libtbb.so' as a
+      # relative symlink pointing back at the versioned library
+      file.rename(lib, versioned)
+      file.symlink(basename(versioned), lib)
+
+   }
+
+}
+
 # Report which TBB libraries are about to be installed, and from where.
 # Stale or unexpected libraries copied here have historically been a
 # subtle source of load failures in downstream packages, so make the