libexpr/NixSymbolTable: Init

The names were prefixed with `sym_` to allow faithfully representing
names that start with __. (Previously the underscores were omitted, at
the cost of readability for people less familiar with the intricate
details of Nix. Is `toString` literally `toString` or is it
`__toString`? etc.) As a bonus, this allows to easily grep for any
symbol through the entire code base to find where it is used. I've done
exactly that and grouped and annotated the symbols based on their usage.

Change-Id: I230fecd9b0b18e0984ac8111c1e6381f45c5abf2

lix/libexpr/symbol-table.hh

@@ -169,4 +169,81 @@ public:
     }
 };
 
+/**
+ * NixSymbolTable extends the generic SymbolTable with pre-filled symbol constants for
+ * all well-known symbol names used in the Nix language.
+ * Besides the convenience aspect, this also improves performances as it does not require a table lookup for
+ * these very commonly used symbols.
+ */
+class NixSymbolTable : public SymbolTable
+{
+public:
+    /* So it turns out that in C++, not only all identifiers starting with `__` are reserved, but also
+     * all identifiers *containing* `__`. However, given our prefix and the usage of triple underscores
+     * we are exceedingly unlikely to ever accidentally hit an actual identifier collision, and given that
+     * we are using custom types such a collision would almost certainly blow up with a loud bang and not
+     * cause any silent failure. We can always easily change to a different (likely worse) naming convention
+     * for our identifiers should we ever run into such a case.
+     */
+    // NOLINTBEGIN(bugprone-reserved-identifier)
+    /* Magic primops */
+    const Symbol sym___sub = create("__sub");
+    const Symbol sym___lessThan = create("__lessThan");
+    const Symbol sym___mul = create("__mul");
+    const Symbol sym___div = create("__div");
+    const Symbol sym___findFile = create("__findFile");
+    const Symbol sym___nixPath = create("__nixPath");
+    /* Parser keywords */
+    const Symbol sym_or = create("or");
+    const Symbol sym_body = create("body"); /* ancient let */
+    /* __pos */
+    const Symbol sym_file = create("file");
+    const Symbol sym_line = create("line");
+    const Symbol sym_column = create("column");
+    /* Evaluator magic attrs */
+    const Symbol sym___overrides = create("__overrides");
+    const Symbol sym___functor = create("__functor");
+    const Symbol sym___toString = create("__toString");
+    /* Symbols for primops/builtins */
+    const Symbol sym_path = create("path"); // builtins.getContext
+    const Symbol sym_prefix = create("prefix"); // builtins.findFile
+    const Symbol sym_startSet = create("startSet"); // builtins.genericClosure
+    const Symbol sym_operator = create("operator"); // builtins.genericClosure
+    const Symbol sym_key = create("key"); // builtins.genericClosure
+    const Symbol sym_right = create("right"); // builtins.partition
+    const Symbol sym_wrong = create("wrong"); // builtins.partition
+    /* Derivation magic attrs */
+    const Symbol sym___ignoreNulls = create("__ignoreNulls");
+    const Symbol sym___structuredAttrs = create("__structuredAttrs");
+    const Symbol sym___contentAddressed = create("__contentAddressed");
+    const Symbol sym___impure = create("__impure");
+    /* Derivation */
+    const Symbol sym_outPath = create("outPath");
+    const Symbol sym_drvPath = create("drvPath");
+    const Symbol sym_meta = create("meta");
+    const Symbol sym_outputs = create("outputs");
+    const Symbol sym_outputName = create("outputName");
+    const Symbol sym_allowedReferences = create("allowedReferences");
+    const Symbol sym_allowedRequisites = create("allowedRequisites");
+    const Symbol sym_disallowedReferences = create("disallowedReferences");
+    const Symbol sym_disallowedRequisites = create("disallowedRequisites");
+    const Symbol sym_maxSize = create("maxSize");
+    const Symbol sym_maxClosureSize = create("maxClosureSize");
+    const Symbol sym_builder = create("builder");
+    const Symbol sym_args = create("args");
+    const Symbol sym_outputHash = create("outputHash");
+    const Symbol sym_outputHashAlgo = create("outputHashAlgo");
+    const Symbol sym_outputHashMode = create("outputHashMode");
+    const Symbol sym_recurseForDerivations = create("recurseForDerivations");
+    const Symbol sym_outputSpecified = create("outputSpecified");
+    /* Flakes */
+    const Symbol sym_description = create("description");
+    const Symbol sym_self = create("self");
+    /* Various uses */
+    const Symbol sym_name = create("name"); // Derivation name, name value pair, ...
+    const Symbol sym_value = create("value"); // builtins.tryEval, name value pair, ...
+    const Symbol sym_system = create("system"); // Derivation, user env, ...
+    const Symbol sym_type = create("type");
+    // NOLINTEND(bugprone-reserved-identifier)
+};
 }