builder: Automatically compress man pages. Resolves serpent-os#16

Compress any man page files found in the manifest with zstd,
if enabled by the packager.

There are three considerations:-
- It _will_ increase the size of the resulting .stone file(s),
  (compressing .stones with --long could resolve this, in the future).
- Info pages are currently ignored but could also be compressed.
- Updating symlinks is not yet tested.

source/mason/build/analysers/compressman.d

@@ -0,0 +1,80 @@
+/*
+ * SPDX-FileCopyrightText: Copyright © 2020-2023 Serpent OS Developers
+ *
+ * SPDX-License-Identifier: Zlib
+ */
+
+/**
+ * mason.build.analysers.compressman;
+ *
+ * Compress man pages with zstd
+ *
+ * Authors: Copyright © 2020-2023 Serpent OS Developers
+ * License: Zlib
+ */
+
+module mason.build.analysers.compressman;
+
+import mason.build.builder : Builder;
+import mason.build.context;
+import moss.core.sizing : formattedSize;
+import std.algorithm : canFind, endsWith;
+import std.experimental.logger;
+import std.file;
+import std.stdio: File, toFile;
+import std.string : format;
+import zstd : compress;
+import std.conv : to;
+public import moss.deps.analysis;
+
+/**
+ * Detect man pages and compress them with zstd
+ *
+ * Params:
+ *      analyser = Scoped analyser for this run
+ *      fileInfo = Current file to run analysis on
+ * Returns: AnalysisReturn.NextFunction always
+ */
+static AnalysisReturn compressManPages(scope Analyser analyser, ref FileInfo fileInfo)
+{
+    if (!buildContext.spec.options.compressman || fileInfo.type != FileType.Regular)
+    {
+        return AnalysisReturn.NextHandler;
+    }
+
+    auto filename = fileInfo.path;
+    auto instance = analyser.userdata!Builder;
+
+    /* Find a man page file */
+    if (filename.canFind("man") && filename.endsWith("1", "2", "3", "4", "5", "6", "7", "8", "9"))
+    {
+        /* We have a symlink file, update it to point to the compressed file */
+        // FIXME: Not tested
+        if ((fileInfo.type == FileType.Symlink) && (fileInfo.type != FileType.Directory))
+        {
+            auto actualpath = std.file.readLink(filename);
+            std.file.symlink(format!"%s.zst"(actualpath), format!"%s.zst"(filename));
+            /* Collect the updated symlink into the manifest */
+            instance.collectPath(format!"%s.zst"(fileInfo.fullPath), instance.installRoot);
+            /* Remove the original file */
+            return AnalysisReturn.IgnoreFile;
+        }
+
+        /* Compress it in memory */
+        auto manfile = std.file.read(fileInfo.fullPath);
+        auto compressedmanfile = compress(manfile, 19);
+        immutable double presize = manfile.length;
+        immutable double postsize = compressedmanfile.length;
+        info(format!"[Man] Compressing: %s. Original size: %s Compressed size: %s"(filename, formattedSize(presize),
+                formattedSize(postsize)));
+
+        /* Write the compressed file to disk */
+        File f = File(format!"%s.zst"(fileInfo.fullPath), "w");
+        f.rawWrite(compressedmanfile);
+        /* Collect the compressed file into the manifest */
+        instance.collectPath(format!"%s.zst"(fileInfo.fullPath), instance.installRoot);
+        /* Remove the original pre-compressed file */
+        return AnalysisReturn.IgnoreFile;
+    }
+    return AnalysisReturn.NextHandler;
+}

source/mason/build/analysers/package.d

@@ -17,6 +17,7 @@ module mason.build.analysers;
 
 public import mason.build.analysers.binary;
 public import mason.build.analysers.cmake;
+public import mason.build.analysers.compressman;
 public import mason.build.analysers.elves;
 public import mason.build.analysers.rejects;
 public import mason.build.analysers.pkgconfig;

source/mason/build/builder.d

@@ -327,6 +327,9 @@ private:
                     &acceptCmakeFiles, &handleCmakeFiles, &includeFile
                     ], 50),
 
+            /* Compress man pages if enabled */
+            AnalysisChain("compressman", [&compressManPages], 40),
+
             /* Default inclusion policy */
             AnalysisChain("default", [&includeFile], 0),
         ];

source/mason/meson.build

@@ -4,6 +4,7 @@ libmason_sources = [
     'package.d',
     'build/analysers/binary.d',
     'build/analysers/cmake.d',
+    'build/analysers/compressman.d',
     'build/analysers/elves.d',
     'build/analysers/package.d',
     'build/analysers/pkgconfig.d',