stage2: implement zig build

As part of this:

 * add std.process.cleanExit. closes #6395
   - use it in several places
 * adjust the alignment of text in `zig build --help` menu
 * Cache: support the concept of "unhit" so that we properly keep track
   of the cache when we find out using the secondary hash that the cache
   "hit" was actually a miss. Use this to fix false negatives of caching
   of stage1 build artifacts.
 * fix not deleting the symlink hash for stage1 build artifacts causing
   false positives.
 * implement support for Package arguments in stage1 build artifacts
 * update and add missing usage text
 * add --override-lib-dir and --enable-cache CLI options
   - `--enable-cache` takes the place of `--cache on`
 * CLI supports -femit-bin=foo combined with --enable-cache to do an
   "update file" operation. --enable-cache without that argument
   will build the output into a cache directory and then print the path
   to stdout (matching master branch behavior).
 * errors surfacing from main() now print "error: Foo" instead of
   "error: error.Foo".

1 files changed, 24 insertions, 13 deletions

diff --git a/src/Cache.zig b/src/Cache.zig
index 24c6ae3ac4..7a0c78a1d9 100644
--- a/src/Cache.zig
+++ b/src/Cache.zig
@@ -120,6 +120,13 @@ pub const HashHelper = struct {
         return copy.final();
     }
 
+    pub fn peekBin(hh: HashHelper) [bin_digest_len]u8 {
+        var copy = hh;
+        var bin_digest: [bin_digest_len]u8 = undefined;
+        copy.hasher.final(&bin_digest);
+        return bin_digest;
+    }
+
     /// Returns a hex encoded hash of the inputs, mutating the state of the hasher.
     pub fn final(hh: *HashHelper) [hex_digest_len]u8 {
         var bin_digest: [bin_digest_len]u8 = undefined;
@@ -338,19 +345,7 @@ pub const CacheHash = struct {
         if (any_file_changed) {
             // cache miss
             // keep the manifest file open
-            // reset the hash
-            self.hash.hasher = hasher_init;
-            self.hash.hasher.update(&bin_digest);
-
-            // Remove files not in the initial hash
-            for (self.files.items[input_file_count..]) |*file| {
-                file.deinit(self.cache.gpa);
-            }
-            self.files.shrinkRetainingCapacity(input_file_count);
-
-            for (self.files.items) |file| {
-                self.hash.hasher.update(&file.bin_digest);
-            }
+            self.unhit(bin_digest, input_file_count);
             return false;
         }
 
@@ -366,6 +361,22 @@ pub const CacheHash = struct {
         return true;
     }
 
+    pub fn unhit(self: *CacheHash, bin_digest: [bin_digest_len]u8, input_file_count: usize) void {
+        // Reset the hash.
+        self.hash.hasher = hasher_init;
+        self.hash.hasher.update(&bin_digest);
+
+        // Remove files not in the initial hash.
+        for (self.files.items[input_file_count..]) |*file| {
+            file.deinit(self.cache.gpa);
+        }
+        self.files.shrinkRetainingCapacity(input_file_count);
+
+        for (self.files.items) |file| {
+            self.hash.hasher.update(&file.bin_digest);
+        }
+    }
+
     fn populateFileHash(self: *CacheHash, ch_file: *File) !void {
         const file = try fs.cwd().openFile(ch_file.path.?, .{});
         defer file.close();