Treat import("file") as hex string

changelog/dmd.import-exp-hexstring.dd

@@ -0,0 +1,12 @@
+Import expressions are now treated as hex strings
+
+While [Import expressions](https://dlang.org/spec/expression.html#import_expressions) are typed as `string`, they are also used to embed binary files.
+By treating them the same as hex strings, they will implicitly convert to arrays of integral types other than `char`.
+
+---
+// Formerly, a cast was required:
+immutable ubyte[] iconImg = cast(immutable ubyte[]) import("icon.png");
+
+// Now, it implicitly converts to integral arrays:
+immutable ubyte[] iconImg = import("icon.png");
+---

compiler/src/dmd/expressionsem.d

@@ -7668,6 +7668,7 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             if (auto fmResult = global.fileManager.lookup(fileName))
             {
                 se = new StringExp(e.loc, fmResult);
+                se.hexString = true;
             }
             else
             {

compiler/test/compilable/import_exp.d

@@ -0,0 +1,36 @@
+// REQUIRED_ARGS: -Jcompilable/imports/
+// EXTRA_FILES: imports/imp16088.d imports/test21227/a..b.txt imports/test21227/a.txt imports/test21227/..foo/a.txt
+
+// https://issues.dlang.org/show_bug.cgi?id=16088
+
+void bar(string x) {}
+auto foo()
+{
+    import("imp16088.d").bar;
+}
+
+
+// https://issues.dlang.org/show_bug.cgi?id=21227
+
+void test21227()
+{
+    import("./test21227/a.txt").bar;
+    import("test21227//a..b.txt").bar;
+    import("test21227/..foo/a.txt").bar;
+
+    version(Windows)
+    {
+        import(r".\test21227\a.txt").bar;
+        import(r"test21227\\a..b.txt").bar;
+        import(r"test21227\..foo\a.txt").bar;
+    }
+}
+
+// Test that it's treated like a hex string, allowing implicit conversion to byte array
+
+// Can't test whole contents because line endings may vary
+enum expectedStart = "module imports.imp16088;";
+
+immutable ubyte[] s0 = import("imp16088.d");
+
+static assert(s0[0 .. expectedStart.length] == "module imports.imp16088;");