fonts: Use a random pangram for fonts supporting English

This patch is a genuine product of Debconf 2018.

data/pangrams/en.txt

@@ -0,0 +1,24 @@
+A quick brown fox jumps over the lazy dog.
+Whenever the black fox jumped the squirrel gazed suspiciously.
+The five boxing wizards jump quickly.
+A large fawn jumped quickly over white zebras in a box.
+We quietly gave Bert a handsome prize for his six juicy pink plums.
+Crazy Fredrick bought many very exquisite opal jewels.
+Five or six big jet planes zoomed quickly past the tower.
+My grandfather picks up quartz and valuable onyx jewels.
+Sphinx of black quartz, judge my vow.
+Two driven jocks help fax my big quiz.
+Five quacking zephyrs jolt my wax bed.
+Pack my box with five dozen liquor jugs.
+Jinxed wizards pluck ivy from the big quilt.
+We promptly judged antique ivory buckles for the next prize.
+A mad boxer shot a quick, gloved jab to the jaw of his dizzy opponent.
+Jaded zombies acted quaintly but kept driving their oxen forward.
+The job requires extra pluck and zeal from every young wage earner.
+Jived fox nymph grabs quick waltz.
+How vexingly quick daft zebras jump!
+Amazingly few discotheques provide jukeboxes.
+The quick onyx goblin jumps over the lazy dwarf.
+Six big devils from Japan quickly forgot how to waltz.
+Jack amazed a few girls by dropping the antique onyx vase.
+A quick movement of the enemy will jeopardize six gunboats.

src/asgen/font.d

@@ -19,7 +19,7 @@
 
 module asgen.font;
 
-import std.string : format, fromStringz, toStringz, toLower, strip;
+import std.string : format, fromStringz, toStringz, toLower, strip, splitLines;
 import std.conv : to;
 import std.path : buildPath, baseName;
 import std.array : empty, appender, replace;
@@ -41,7 +41,9 @@ import asgen.config : Config;
 
 // global font icon text lookup table, initialized by the constructor or Font and valid (and in memory)
 // as long as the generator runs.
-private static string[string] iconTexts;
+private __gshared static string[string] iconTexts;
+
+private __gshared static string[] englishPangrams = import("pangrams/en.txt").splitLines ();
 
 /**
  * Representation of a single font file.
@@ -114,8 +116,8 @@ public:
             if (err != 0)
                 throw new Exception ("Unable to load font face from file. Error code: %s".format (err));
 
-                loadFontConfigData (fname);
-                fileBaseName = fname.baseName;
+            loadFontConfigData (fname);
+            fileBaseName = fname.baseName;
         }
     }
 
@@ -307,6 +309,24 @@ public:
         import std.uni : byGrapheme, isGraphical, byCodePoint, Grapheme;
         import std.range;
 
+        string randomEnglishPangram ()
+        {
+            import std.digest.crc : crc32Of;
+            import std.conv : to;
+            import std.bitmanip : read;
+
+            auto tmpFontId = this.family;
+            if (tmpFontId.empty)
+                tmpFontId = this.fileBaseName;
+
+            // we do want deterministic results here, so base the "random"
+            // pangram on the font family / font base name
+	        auto hash = crc32Of (tmpFontId).to!(ubyte[]);
+            immutable pangramId = hash.read!uint % englishPangrams.length;
+
+            return englishPangrams[pangramId];
+        }
+
         void setFallbackSampleTextIfRequired ()
         {
             if (sampleText_.empty)
@@ -341,18 +361,22 @@ public:
         // determine our sample texts
         foreach (ref lang; tmpLangList) {
             auto plang = pango_language_from_string (lang.toStringz);
-            auto text = pango_language_get_sample_string (plang).fromStringz;
+            string text;
+            if (lang == "en")
+                text = randomEnglishPangram ();
+            else
+                text = pango_language_get_sample_string (plang).fromStringz.to!string;
 
-			if (text.empty)
-				continue;
+            if (text.empty)
+                continue;
 
-            sampleText_ = text.dup;
+            sampleText_ = text;
             const itP = lang in iconTexts;
             if (itP !is null) {
                 sampleIconText_ = *itP;
                 break;
             }
-		}
+        }
 
         // set some default values if we have been unable to find any texts
         setFallbackSampleTextIfRequired ();

src/asgen/meson.build

@@ -7,6 +7,8 @@ configure_file(input : 'defines.d.in',
                configuration: conf_data
 )
 
+data_import_dirs = include_directories('../../data')
+
 #
 # Sources
 #
@@ -93,6 +95,7 @@ asgen_exe = executable('appstream-generator',
                    fontconfig_dep,
                    pango_dep],
     link_with: [girbind_lib],
+    d_import_dirs: [data_import_dirs],
     install: true
 )
 
@@ -115,6 +118,7 @@ asgen_test_exe = executable('asgen_test',
                    fontconfig_dep,
                    pango_dep],
     link_with: [girbind_lib],
+    d_import_dirs: [data_import_dirs],
     d_unittest: true
 )
 test('asgen_tests', asgen_test_exe)