From 9f8f440b6e66da383957162731f50c9985052841 Mon Sep 17 00:00:00 2001
From: Stefan Merettig <stefan-merettig@nuriaproject.org>
Date: Mon, 22 Jun 2020 18:59:45 +0200
Subject: [PATCH] clang/find_clang.cr: Auto-detect if linking libclang using .a
 or .so

ArchLinux has changed their mind in the meantime.  Didn't feel like
messing with the environment variable, instead, it's supposed to
auto-detect now if libclang.a or libclang.so exist.

If both static and dynamic versions are available it'll prefer the
static library, which is hopefully more stable when the user decides
to update their system.

The user can still use BINDGEN_DYNAMIC=1/0 as before, but simply not
setting it will trigger the auto-detection.

Also, the pattern-matching style "case" statement of Crystal is some
good stuff!
---
 clang/find_clang.cr | 42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

diff --git a/clang/find_clang.cr b/clang/find_clang.cr
index ab0dcc7..7010821 100644
--- a/clang/find_clang.cr
+++ b/clang/find_clang.cr
@@ -44,8 +44,15 @@ if dynamic.nil?
     end
   end
 end
-dynamic = dynamic.try &.==("1") || false
-log "Link against LLVM shared libraries: #{dynamic}. (Adjust with env BINDGEN_DYNAMIC=0/1 if needed)"
+dynamic = dynamic.try &.==("1")
+
+dynamic_s = case dynamic
+            when true then  "Dynamically"
+            when false then "Statically"
+            else            "Auto-Detect"
+            end
+
+log "Link against LLVM shared libraries: #{dynamic_s}. (Adjust with env BINDGEN_DYNAMIC=0/1 if needed)"
 
 # Determine which llvm-config we are using
 unless OPTIONS[:llvm_config] ||= find_llvm_config_binary min_version: "6.0.0"
@@ -344,19 +351,28 @@ def shell_split(line : String)
   end
 end
 
+def find_library_candidates(paths, prefix, suffix)
+  paths
+    .flat_map { |path| Dir["#{path}/lib#{prefix}*.#{suffix}"] }
+    .map { |path| File.basename(path)[/^lib(.+)\.#{suffix}$/, 1] }
+    .uniq
+end
+
 # Finds all LLVM and clang libraries, and links to them.  We don't need
 # all of them - Which totally helps with keeping linking times low.
-def find_libraries(paths, prefix, dynamic=false)
-  if dynamic
-    paths
-      .flat_map { |path| Dir["#{path}/lib#{prefix}*.so"] }
-      .map { |path| File.basename(path)[/^lib(.+)\.so$/, 1] }
-      .uniq
-  else
-    paths
-      .flat_map { |path| Dir["#{path}/lib#{prefix}*.a"] }
-      .map { |path| File.basename(path)[/^lib([^.]+)\.a$/, 1] } # FIXME: this lead to crash for e.g. libclang_rt.msan_cxx-x86_64.a
-      .uniq
+def find_libraries(paths, prefix, dynamic : Bool? = nil)
+  # TODO: Windows support.
+
+  dynamics = find_library_candidates(paths, prefix, "so")
+  statics = find_library_candidates(paths, prefix, "a")
+  # FIXME: This also finds unwanted libraries like libclang_rt.msan_cxx-x86_64.a
+  #        which can cause a crash later on.
+
+  case {dynamic, statics.empty?}
+  when {true, _} then   dynamics
+  when {false, _} then  statics
+  when {nil, true} then dynamics
+  else                  statics
   end
 end