new compiler feature: --expandMacro

changelog.md

@@ -271,6 +271,9 @@ proc enumToString*(enums: openArray[enum]): string =
 - The `--hotCodeReloading` has been implemented for the native targets.
   The compiler also provides a new more flexible API for handling the
   hot code reloading events in the code.
+- The compiler nows supports a ``--expandMacro:macroNameHere`` switch
+  for easy introspection into what a macro expands into.
+
 
 
 ### Bugfixes

compiler/commands.nim

@@ -27,7 +27,7 @@ bootSwitch(usedNoGC, defined(nogc), "--gc:none")
 import
   os, msgs, options, nversion, condsyms, strutils, extccomp, platform,
   wordrecg, parseutils, nimblecmd, idents, parseopt, sequtils, lineinfos,
-  pathutils
+  pathutils, strtabs
 
 # but some have deps to imported modules. Yay.
 bootSwitch(usedTinyC, hasTinyCBackend, "-d:tinyc")
@@ -774,6 +774,9 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
     processOnOffSwitchG(conf, {optDocInternal}, arg, pass, info)
   of "multimethods":
     processOnOffSwitchG(conf, {optMultiMethods}, arg, pass, info)
+  of "expandmacro":
+    expectArg(conf, switch, arg, pass, info)
+    conf.macrosToExpand[arg] = "T"
   of "":
     conf.projectName = "-"
   else:

compiler/lineinfos.nim

@@ -44,7 +44,7 @@ type
     hintConditionAlwaysTrue, hintConditionAlwaysFalse, hintName, hintPattern,
     hintExecuting, hintLinking, hintDependency,
     hintSource, hintPerformance, hintStackTrace, hintGCStats,
-    hintGlobalVar,
+    hintGlobalVar, hintExpandMacro,
     hintUser, hintUserRaw,
     hintExtendedContext
 
@@ -117,6 +117,7 @@ const
     hintStackTrace: "$1",
     hintGCStats: "$1",
     hintGlobalVar: "global variable declared here",
+    hintExpandMacro: "expanded macro: $1",
     hintUser: "$1",
     hintUserRaw: "$1",
     hintExtendedContext: "$1",
@@ -141,7 +142,7 @@ const
     "XDeclaredButNotUsed", "ConvToBaseNotNeeded", "ConvFromXtoItselfNotNeeded",
     "ExprAlwaysX", "QuitCalled", "Processing", "CodeBegin", "CodeEnd", "Conf",
     "Path", "CondTrue", "CondFalse", "Name", "Pattern", "Exec", "Link", "Dependency",
-    "Source", "Performance", "StackTrace", "GCStats", "GlobalVar",
+    "Source", "Performance", "StackTrace", "GCStats", "GlobalVar", "ExpandMacro",
     "User", "UserRaw", "ExtendedContext",
   ]
 

compiler/options.nim

@@ -180,6 +180,7 @@ type
     linesCompiled*: int  # all lines that have been compiled
     options*: TOptions    # (+)
     globalOptions*: TGlobalOptions # (+)
+    macrosToExpand*: StringTableRef
     m*: MsgConfig
     evalTemplateCounter*: int
     evalMacroCounter*: int
@@ -308,6 +309,7 @@ proc newConfigRef*(): ConfigRef =
     verbosity: 1,
     options: DefaultOptions,
     globalOptions: DefaultGlobalOptions,
+    macrosToExpand: newStringTable(modeStyleInsensitive),
     m: initMsgConfig(),
     evalExpr: "",
     cppDefines: initSet[string](),

compiler/sem.nim

@@ -16,7 +16,7 @@ import
   procfind, lookups, pragmas, passes, semdata, semtypinst, sigmatch,
   intsets, transf, vmdef, vm, idgen, aliases, cgmeth, lambdalifting,
   evaltempl, patterns, parampatterns, sempass2, linter, semmacrosanity,
-  lowerings, pluginsupport, plugins/active, rod, lineinfos
+  lowerings, pluginsupport, plugins/active, rod, lineinfos, strtabs
 
 from modulegraphs import ModuleGraph, PPassContext, onUse, onDef, onDefResolveForward
 
@@ -467,6 +467,8 @@ proc semMacroExpr(c: PContext, n, nOrig: PNode, sym: PSym,
   result = evalMacroCall(c.module, c.graph, n, nOrig, sym)
   if efNoSemCheck notin flags:
     result = semAfterMacroCall(c, n, result, sym, flags)
+  if c.config.macrosToExpand.hasKey(sym.name.s):
+    message(c.config, nOrig.info, hintExpandMacro, renderTree(result))
   result = wrapInComesFrom(nOrig.info, sym, result)
   popInfoContext(c.config)
 

doc/advopt.txt

@@ -103,6 +103,7 @@ Advanced options:
   --cppCompileToNamespace:namespace
                             use the provided namespace for the generated C++ code,
                             if no namespace is provided "Nim" will be used
+  --expandMacro:MACRO       dump every generated AST from MACRO
   --excludePath:PATH        exclude a path from the list of search paths
   --dynlibOverride:SYMBOL   marks SYMBOL so that dynlib:SYMBOL
                             has no effect and can be statically linked instead;

tests/compilerfeatures/texpandmacro.nim

@@ -0,0 +1,18 @@
+discard """
+  cmd: "nim c --expandMacro:foo $file"
+  nimout: '''Hint: expanded macro:
+echo ["injected echo"]
+var x = 4 [ExpandMacro]
+'''
+  output: '''injected echo'''
+"""
+
+import macros
+
+macro foo(x: untyped): untyped =
+  result = quote do:
+    echo "injected echo"
+    `x`
+
+foo:
+  var x = 4