Use C++20 concepts to require constraints on template parameters (#1977)

src/asm/charmap.cpp

@@ -3,6 +3,7 @@
 #include "asm/charmap.hpp"
 
 #include <algorithm>
+#include <concepts> // predicate
 #include <map>
 #include <optional>
 #include <stack>
@@ -65,8 +66,9 @@ struct Charmap {
 };
 
 // Traverse the trie depth-first to derive the character mappings in definition order
-template<typename CallbackFnT>
-bool forEachChar(Charmap const &charmap, CallbackFnT callback) {
+bool forEachChar(
+    Charmap const &charmap, std::predicate<size_t, std::string const &> auto callback
+) {
 	// clang-format off: nested initializers
 	for (std::stack<std::pair<size_t, std::string>> prefixes({{0, ""}}); !prefixes.empty();) {
 		// clang-format on

src/asm/lexer.cpp

@@ -4,6 +4,7 @@
 #include <sys/stat.h>
 
 #include <algorithm>
+#include <concepts> // predicate
 #include <errno.h>
 #include <fcntl.h>
 #include <fstream>
@@ -527,6 +528,7 @@ static void shiftChar();
 static int bumpChar();
 static int nextChar();
 template<uint32_t Base>
+    requires BaseV<Base>
 static uint32_t readNumber(int initial, char const *prefix);
 
 static uint32_t readBracketedMacroArgNum() {
@@ -818,8 +820,7 @@ static int nextChar() {
 	return peek();
 }
 
-template<typename PredicateFnT>
-static int skipChars(PredicateFnT predicate) {
+static int skipChars(std::predicate<int> auto predicate) {
 	int c = peek();
 	while (predicate(c)) {
 		c = nextChar();
@@ -1099,6 +1100,7 @@ void lexer_SetGfxDigits(char const digits[4]) {
 }
 
 template<uint32_t Base>
+    requires BaseV<Base>
 static uint32_t readNumber(int initial, char const *prefix) {
 	auto isSomeDigit = [](int c) {
 		if constexpr (Base == 2) {
@@ -2283,8 +2285,7 @@ yy::parser::symbol_type yylex() {
 	}
 }
 
-template<typename CallbackFnT>
-static Capture makeCapture(char const *name, CallbackFnT callback) {
+static Capture makeCapture(char const *name, InvocableR<int, int> auto callback) {
 	// Due to parser internals, it reads the EOL after the expression before calling this.
 	// Thus, we don't need to keep one in the buffer afterwards.
 	// The following assumption checks that.

src/asm/parser.y

@@ -32,6 +32,7 @@
 
 %code {
 	#include <algorithm>
+	#include <concepts> // invocable
 	#include <inttypes.h>
 	#include <optional>
 	#include <stdio.h>
@@ -57,9 +58,10 @@
 
 	yy::parser::symbol_type yylex(); // Provided by lexer.cpp
 
-	template<typename NumCallbackFnT, typename StrCallbackFnT>
 	static auto handleSymbolByType(
-	    std::string const &symName, NumCallbackFnT numCallback, StrCallbackFnT strCallback
+	    std::string const &symName,
+	    std::invocable<Expression const &> auto numCallback,
+	    std::invocable<std::string const &> auto strCallback
 	) {
 		if (Symbol *sym = sym_FindScopedSymbol(symName); sym && sym->type == SYM_EQUS) {
 			return strCallback(*sym->getEqus());