`--usenimcache` (implied by `nim r main`) now caches some compile options to avoid recompiling when project was previously compiled with such options. (#17829)

* `--usenimcache` (implied by `nim r main`) now caches some compile options
to avoid recompiling when project was previously compiled with such options.

* works
* add test
* changelog
* use std/with

3 files changed, 43 insertions, 40 deletions

diff --git a/compiler/extccomp.nim b/compiler/extccomp.nim
index 71a20fc47..3b415c499 100644
--- a/compiler/extccomp.nim
+++ b/compiler/extccomp.nim
@@ -934,9 +934,14 @@ proc callCCompiler*(conf: ConfigRef) =
     script.add("\n")
     generateScript(conf, script)
 
-
 template hashNimExe(): string = $secureHashFile(os.getAppFilename())
 
+proc jsonBuildInstructionsFile*(conf: ConfigRef): AbsoluteFile =
+  # `outFile` is better than `projectName`, as it allows having different json
+  # files for a given source file compiled with different options; it also
+  # works out of the box with `hashMainCompilationParams`.
+  result = getNimcacheDir(conf) / conf.outFile.changeFileExt("json")
+
 proc writeJsonBuildInstructions*(conf: ConfigRef) =
   template lit(x: string) = f.write x
   template str(x: string) =
@@ -993,8 +998,7 @@ proc writeJsonBuildInstructions*(conf: ConfigRef) =
 
 
   var buf = newStringOfCap(50)
-
-  let jsonFile = conf.getNimcacheDir / RelativeFile(conf.projectName & ".json")
+  let jsonFile = conf.jsonBuildInstructionsFile
   conf.jsonBuildFile = jsonFile
   let output = conf.absOutFile
 
@@ -1038,8 +1042,7 @@ proc writeJsonBuildInstructions*(conf: ConfigRef) =
     lit "\L}\L"
     close(f)
 
-proc changeDetectedViaJsonBuildInstructions*(conf: ConfigRef; projectfile: AbsoluteFile): bool =
-  let jsonFile = toGeneratedFile(conf, projectfile, "json")
+proc changeDetectedViaJsonBuildInstructions*(conf: ConfigRef; jsonFile: AbsoluteFile): bool =
   if not fileExists(jsonFile): return true
   if not fileExists(conf.absOutFile): return true
   result = false
@@ -1090,11 +1093,9 @@ proc changeDetectedViaJsonBuildInstructions*(conf: ConfigRef; projectfile: Absol
     echo "Warning: JSON processing failed: ", getCurrentExceptionMsg()
     result = true
 
-proc runJsonBuildInstructions*(conf: ConfigRef; projectfile: AbsoluteFile) =
-  let jsonFile = toGeneratedFile(conf, projectfile, "json")
+proc runJsonBuildInstructions*(conf: ConfigRef; jsonFile: AbsoluteFile) =
   try:
     let data = json.parseFile(jsonFile.string)
-
     let output = data["outputFile"].getStr
     createDir output.parentDir
     let outputCurrent = $conf.absOutFile
diff --git a/compiler/main.nim b/compiler/main.nim
index 9c9a789cb..48fbd185c 100644
--- a/compiler/main.nim
+++ b/compiler/main.nim
@@ -19,7 +19,7 @@ import
   cgen, json, nversion,
   platform, nimconf, passaux, depends, vm,
   modules,
-  modulegraphs, tables, lineinfos, pathutils, vmprofiler
+  modulegraphs, tables, lineinfos, pathutils, vmprofiler, std/[sha1, with]
 
 import ic / [cbackend, integrity, navigator]
 from ic / ic import rodViewer
@@ -80,15 +80,13 @@ when not defined(leanCompiler):
 
 proc commandCompileToC(graph: ModuleGraph) =
   let conf = graph.config
-  setOutFile(conf)
   extccomp.initVars(conf)
   semanticPasses(graph)
   if conf.symbolFiles == disabledSf:
     registerPass(graph, cgenPass)
 
     if {optRun, optForceFullMake} * conf.globalOptions == {optRun} or isDefined(conf, "nimBetterRun"):
-      let proj = changeFileExt(conf.projectFull, "")
-      if not changeDetectedViaJsonBuildInstructions(conf, proj):
+      if not changeDetectedViaJsonBuildInstructions(conf, conf.jsonBuildInstructionsFile):
         # nothing changed
         graph.config.notes = graph.config.mainPackageNotes
         return
@@ -117,27 +115,20 @@ proc commandCompileToC(graph: ModuleGraph) =
       writeDepsFile(graph)
 
 proc commandJsonScript(graph: ModuleGraph) =
-  let proj = changeFileExt(graph.config.projectFull, "")
-  extccomp.runJsonBuildInstructions(graph.config, proj)
+  extccomp.runJsonBuildInstructions(graph.config, graph.config.jsonBuildInstructionsFile)
 
 proc commandCompileToJS(graph: ModuleGraph) =
+  let conf = graph.config
   when defined(leanCompiler):
-    globalError(graph.config, unknownLineInfo, "compiler wasn't built with JS code generator")
+    globalError(conf, unknownLineInfo, "compiler wasn't built with JS code generator")
   else:
-    let conf = graph.config
     conf.exc = excCpp
-
-    if conf.outFile.isEmpty:
-      conf.outFile = RelativeFile(conf.projectName & ".js")
-
-    #incl(gGlobalOptions, optSafeCode)
-    setTarget(graph.config.target, osJS, cpuJS)
-    #initDefines()
-    defineSymbol(graph.config.symbols, "ecmascript") # For backward compatibility
+    setTarget(conf.target, osJS, cpuJS)
+    defineSymbol(conf.symbols, "ecmascript") # For backward compatibility
     semanticPasses(graph)
     registerPass(graph, JSgenPass)
     compileProject(graph)
-    if optGenScript in graph.config.globalOptions:
+    if optGenScript in conf.globalOptions:
       writeDepsFile(graph)
 
 proc interactivePasses(graph: ModuleGraph) =
@@ -186,6 +177,31 @@ proc commandView(graph: ModuleGraph) =
 const
   PrintRopeCacheStats = false
 
+proc hashMainCompilationParams*(conf: ConfigRef): string =
+  ## doesn't have to be complete; worst case is a cache hit and recompilation.
+  var state = newSha1State()
+  with state:
+    update os.getAppFilename() # nim compiler
+    update conf.commandLine # excludes `arguments`, as it should
+    update $conf.projectFull # so that running `nim r main` from 2 directories caches differently
+  result = $SecureHash(state.finalize())
+
+proc setOutFile*(conf: ConfigRef) =
+  proc libNameTmpl(conf: ConfigRef): string {.inline.} =
+    result = if conf.target.targetOS == osWindows: "$1.lib" else: "lib$1.a"
+
+  if conf.outFile.isEmpty:
+    var base = conf.projectName
+    if optUseNimcache in conf.globalOptions:
+      base.add "_" & hashMainCompilationParams(conf)
+    let targetName =
+      if conf.backend == backendJs: base & ".js"
+      elif optGenDynLib in conf.globalOptions:
+        platform.OS[conf.target.targetOS].dllFrmt % base
+      elif optGenStaticLib in conf.globalOptions: libNameTmpl(conf) % base
+      else: base & platform.OS[conf.target.targetOS].exeExt
+    conf.outFile = RelativeFile targetName
+
 proc mainCommand*(graph: ModuleGraph) =
   let conf = graph.config
   let cache = graph.cache
@@ -220,6 +236,7 @@ proc mainCommand*(graph: ModuleGraph) =
 
   proc compileToBackend() =
     customizeForBackend(conf.backend)
+    setOutFile(conf)
     case conf.backend
     of backendC: commandCompileToC(graph)
     of backendCpp: commandCompileToC(graph)
diff --git a/compiler/options.nim b/compiler/options.nim
index 7044e64bd..209564d0a 100644
--- a/compiler/options.nim
+++ b/compiler/options.nim
@@ -970,18 +970,3 @@ proc floatInt64Align*(conf: ConfigRef): int16 =
       # to 4bytes (except with -malign-double)
       return 4
   return 8
-
-proc setOutFile*(conf: ConfigRef) =
-  proc libNameTmpl(conf: ConfigRef): string {.inline.} =
-    result = if conf.target.targetOS == osWindows: "$1.lib" else: "lib$1.a"
-
-  if conf.outFile.isEmpty:
-    let base = conf.projectName
-    let targetName =
-      if optGenDynLib in conf.globalOptions:
-        platform.OS[conf.target.targetOS].dllFrmt % base
-      elif optGenStaticLib in conf.globalOptions:
-        libNameTmpl(conf) % base
-      else:
-        base & platform.OS[conf.target.targetOS].exeExt
-    conf.outFile = RelativeFile targetName