From e5d479b06e74e04b3ef3108e6098424b2130cbe5 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sat, 4 Apr 2020 12:26:57 -0400
Subject: [PATCH] detect an endless loop when trying to detect native libc
 installation

closes #4810
---
 src-self-hosted/libc_installation.zig | 19 +++++++++++++++++++
 src-self-hosted/stage2.zig            |  2 ++
 src/error.cpp                         |  1 +
 src/stage2.h                          |  1 +
 4 files changed, 23 insertions(+)

diff --git a/src-self-hosted/libc_installation.zig b/src-self-hosted/libc_installation.zig
index f3441cec0d..db9db64a67 100644
--- a/src-self-hosted/libc_installation.zig
+++ b/src-self-hosted/libc_installation.zig
@@ -32,6 +32,7 @@ pub const LibCInstallation = struct {
         LibCKernel32LibNotFound,
         UnsupportedArchitecture,
         WindowsSdkNotFound,
+        ZigIsTheCCompiler,
     };
 
     pub fn parse(
@@ -229,10 +230,19 @@ pub const LibCInstallation = struct {
             "-xc",
             dev_null,
         };
+        var env_map = try std.process.getEnvMap(allocator);
+        defer env_map.deinit();
+
+        // Detect infinite loops.
+        const inf_loop_env_key = "ZIG_IS_DETECTING_LIBC_PATHS";
+        if (env_map.get(inf_loop_env_key) != null) return error.ZigIsTheCCompiler;
+        try env_map.set(inf_loop_env_key, "1");
+
         const exec_res = std.ChildProcess.exec(.{
             .allocator = allocator,
             .argv = &argv,
             .max_output_bytes = 1024 * 1024,
+            .env_map = &env_map,
             // Some C compilers, such as Clang, are known to rely on argv[0] to find the path
             // to their own executable, without even bothering to resolve PATH. This results in the message:
             // error: unable to execute command: Executable "" doesn't exist!
@@ -518,10 +528,19 @@ fn ccPrintFileName(args: CCPrintFileNameOptions) ![:0]u8 {
     defer allocator.free(arg1);
     const argv = [_][]const u8{ cc_exe, arg1 };
 
+    var env_map = try std.process.getEnvMap(allocator);
+    defer env_map.deinit();
+
+    // Detect infinite loops.
+    const inf_loop_env_key = "ZIG_IS_DETECTING_LIBC_PATHS";
+    if (env_map.get(inf_loop_env_key) != null) return error.ZigIsTheCCompiler;
+    try env_map.set(inf_loop_env_key, "1");
+
     const exec_res = std.ChildProcess.exec(.{
         .allocator = allocator,
         .argv = &argv,
         .max_output_bytes = 1024 * 1024,
+        .env_map = &env_map,
         // Some C compilers, such as Clang, are known to rely on argv[0] to find the path
         // to their own executable, without even bothering to resolve PATH. This results in the message:
         // error: unable to execute command: Executable "" doesn't exist!
diff --git a/src-self-hosted/stage2.zig b/src-self-hosted/stage2.zig
index bfc49a876b..3f96ff2110 100644
--- a/src-self-hosted/stage2.zig
+++ b/src-self-hosted/stage2.zig
@@ -115,6 +115,7 @@ const Error = extern enum {
     InvalidOperatingSystemVersion,
     UnknownClangOption,
     NestedResponseFile,
+    ZigIsTheCCompiler,
 };
 
 const FILE = std.c.FILE;
@@ -868,6 +869,7 @@ export fn stage2_libc_find_native(stage1_libc: *Stage2LibCInstallation) Error {
         error.LibCKernel32LibNotFound => return .LibCKernel32LibNotFound,
         error.UnsupportedArchitecture => return .UnsupportedArchitecture,
         error.WindowsSdkNotFound => return .WindowsSdkNotFound,
+        error.ZigIsTheCCompiler => return .ZigIsTheCCompiler,
     };
     stage1_libc.initFromStage2(libc);
     return .None;
diff --git a/src/error.cpp b/src/error.cpp
index 76b510ecf3..0ca7d25b79 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -85,6 +85,7 @@ const char *err_str(Error err) {
         case ErrorInvalidOperatingSystemVersion: return "invalid operating system version";
         case ErrorUnknownClangOption: return "unknown Clang option";
         case ErrorNestedResponseFile: return "nested response file";
+        case ErrorZigIsTheCCompiler: return "Zig was not provided with libc installation information, and so it does not know where the libc paths are on the system. Zig attempted to use the system C compiler to find out where the libc paths are, but discovered that Zig is being used as the system C compiler.";
     }
     return "(invalid error)";
 }
diff --git a/src/stage2.h b/src/stage2.h
index e397291f52..7dd2de988e 100644
--- a/src/stage2.h
+++ b/src/stage2.h
@@ -107,6 +107,7 @@ enum Error {
     ErrorInvalidOperatingSystemVersion,
     ErrorUnknownClangOption,
     ErrorNestedResponseFile,
+    ErrorZigIsTheCCompiler,
 };
 
 // ABI warning