eval: add comptime-if support (#24919)

vlib/v/eval/eval.v

@@ -202,15 +202,104 @@ pub fn (mut e Eval) register_symbol_stmts(stmts []ast.Stmt, mod string, file str
 pub fn (mut e Eval) comptime_cond(cond ast.Expr) bool {
 	match cond {
 		ast.Ident {
-			match cond.name {
-				'native' {
-					return false
+			cname := cond.name
+			if cname in ast.valid_comptime_if_os {
+				mut ident_result := false
+				if !e.pref.output_cross_c {
+					if cname_enum_val := pref.os_from_string(cname) {
+						if cname_enum_val == e.pref.os {
+							ident_result = true
+						}
+					}
 				}
-				'windows' {
-					return e.pref.os == .windows
+				$if trace_comptime_os_checks ? {
+					eprintln('>>> ident_name: ${ident_name} | e.pref.os: ${e.pref.os} | ident_result: ${ident_result}')
 				}
-				else {
-					e.error('unknown compile time if')
+				return ident_result
+			} else if cname in ast.valid_comptime_if_compilers {
+				return pref.cc_from_string(cname) == e.pref.ccompiler_type
+			} else if cname in ast.valid_comptime_if_platforms {
+				match cname {
+					'amd64' { return e.pref.arch == .amd64 }
+					'i386' { return e.pref.arch == .i386 }
+					'aarch64' { return e.pref.arch == .arm64 }
+					'arm64' { return e.pref.arch == .arm64 }
+					'arm32' { return e.pref.arch == .arm32 }
+					'rv64' { return e.pref.arch == .rv64 }
+					'rv32' { return e.pref.arch == .rv32 }
+					's390x' { return e.pref.arch == .s390x }
+					'ppc64le' { return e.pref.arch == .ppc64le }
+					'loongarch64' { return e.pref.arch == .loongarch64 }
+					else { e.error('unknown comptime platforms \$if ${cname}') }
+				}
+			} else if cname in ast.valid_comptime_if_cpu_features {
+				match cname {
+					'x64' { e.pref.m64 }
+					'x32' { !e.pref.m64 }
+					else { e.error('unknown comptime cpu features \$if ${cname}') }
+				}
+			} else if cname in ast.valid_comptime_if_other {
+				match cname {
+					'apk' {
+						return e.pref.is_apk
+					}
+					'js' {
+						return e.pref.backend.is_js()
+					}
+					'debug' {
+						return e.pref.is_debug
+					}
+					'prod' {
+						return e.pref.is_prod
+					}
+					'profile' {
+						return e.pref.is_prof
+					}
+					'test' {
+						return e.pref.is_test
+					}
+					'musl' {
+						e.error('unknown comptime other \$if ${cname}')
+					}
+					'glibc' {
+						e.error('unknown comptime other \$if ${cname}')
+					}
+					'threads' {
+						return e.table.gostmts > 0
+					}
+					'prealloc' {
+						return e.pref.prealloc
+					}
+					'no_bounds_checking' {
+						return cname in e.pref.compile_defines_all
+					}
+					'autofree' {
+						return e.pref.autofree
+					}
+					'freestanding' {
+						return e.pref.is_bare && !e.pref.output_cross_c
+					}
+					'interpreter' {
+						return e.pref.backend == .interpret
+					}
+					'es5' {
+						return e.pref.output_es5
+					}
+					'wasm32' {
+						return e.pref.os == .wasm32
+					}
+					'wasm32_wasi' {
+						return e.pref.os == .wasm32_wasi
+					}
+					'fast_math' {
+						return e.pref.fast_math
+					}
+					'native' {
+						return e.pref.backend == .native
+					}
+					else {
+						e.error('unknown comptime other \$if ${cname}')
+					}
 				}
 			}
 		}

vlib/v/eval/expr.c.v

@@ -1,6 +1,5 @@
 module eval
 
-import v.pref
 import v.ast
 import v.util
 import math
@@ -145,36 +144,13 @@ pub fn (mut e Eval) expr(expr ast.Expr, expecting ast.Type) Object {
 			return Object(res)
 		}
 		ast.IfExpr {
-			if expr.is_expr {
-				e.error('`if` expressions not supported')
-			}
-
 			if expr.is_comptime {
 				for i, branch in expr.branches {
-					mut do_if := false
-					if expr.has_else && i + 1 == expr.branches.len { // else branch
-						do_if = true
-					} else {
-						if branch.cond is ast.Ident {
-							if known_os := pref.os_from_string(branch.cond.name) {
-								do_if = e.pref.os == known_os
-							} else {
-								match branch.cond.name {
-									'prealloc' {
-										do_if = e.pref.prealloc
-									}
-									else {
-										e.error('unknown compile time if: ${branch.cond.name}')
-									}
-								}
-							}
-						} else if branch.cond is ast.PostfixExpr {
-							do_if = (branch.cond.expr as ast.Ident).name in e.pref.compile_defines
-						}
-					}
-					if do_if {
+					if e.comptime_cond(branch.cond) || expr.branches.len == i + 1 {
+						e.returning = true
+						e.return_values = []
 						e.stmts(branch.stmts)
-						break
+						return e.return_values[0]
 					}
 				}
 				return empty

vlib/v/eval/stmt.v

@@ -17,7 +17,10 @@ pub fn (mut e Eval) stmts(stmts []ast.Stmt) {
 pub fn (mut e Eval) stmt(stmt ast.Stmt) {
 	match stmt {
 		ast.ExprStmt {
-			e.expr(stmt.expr, stmt.typ)
+			ret := e.expr(stmt.expr, stmt.typ)
+			if e.returning {
+				e.return_values << ret
+			}
 		}
 		ast.AssignStmt {
 			// if stmt.left.len != 1 {

vlib/v/eval/tests/comptime_if_test.v

@@ -0,0 +1,21 @@
+import v.eval
+
+fn test_comptime_if() {
+	mut e := eval.create()
+
+	ret := e.run('const a = 
+	\$if amd64 { "amd" } 
+	\$else \$if i386        { "i386" } 
+	\$else \$if aarch64     { "aarch64" } 
+	\$else \$if arm64       { "arm64" } 
+	\$else \$if arm32       { "arm32" } 
+	\$else \$if rv64        { "rv64" } 
+	\$else \$if rv32        { "rv32" } 
+	\$else \$if s390x       { "s390x" } 
+	\$else \$if ppc64le     { "ppc64le" } 
+	\$else \$if loongarch64 { "loongarch64" } 
+	\$else { "unknown" }')!
+	dump(ret)
+	assert ret[0].string().len != 0
+	assert ret[0].string() != 'unknown'
+}