--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

tests/misc/mbetterrun.nim

@@ -0,0 +1,3 @@
+const mbetterrunVal {.strdefine.} = ""
+static: echo "compiling: " & mbetterrunVal
+echo "running: " & mbetterrunVal

tests/misc/trunner.nim

@@ -29,13 +29,18 @@ const
   nimcache = buildDir / "nimcacheTrunner"
     # instead of `querySetting(nimcacheDir)`, avoids stomping on other parallel tests
 
-proc runCmd(file, options = ""): auto =
+proc runNimCmd(file, options = "", rtarg = ""): auto =
   let fileabs = testsDir / file.unixToNativePath
   doAssert fileabs.fileExists, fileabs
-  let cmd = fmt"{nim} {mode} {options} --hints:off {fileabs}"
+  let cmd = fmt"{nim} {mode} {options} --hints:off {fileabs} {rtarg}"
   result = execCmdEx(cmd)
   when false:  echo result[0] & "\n" & result[1] # for debugging
 
+proc runNimCmdChk(file, options = "", rtarg = ""): string =
+  let (ret, status) = runNimCmd(file, options, rtarg = rtarg)
+  doAssert status == 0, $(file, options) & "\n" & ret
+  ret
+
 when defined(nimTrunnerFfi):
   block: # mevalffi
     when defined(openbsd):
@@ -53,8 +58,8 @@ when defined(nimTrunnerFfi):
 hello world stderr
 hi stderr
 """
-    let (output, exitCode) = runCmd("vm/mevalffi.nim", fmt"{opt} --experimental:compiletimeFFI")
-    let expected = fmt"""
+    let output = runNimCmdChk("vm/mevalffi.nim", fmt"{opt} --experimental:compiletimeFFI")
+    doAssert output == fmt"""
 {prefix}foo
 foo:100
 foo:101
@@ -62,12 +67,10 @@ foo:102:103
 foo:102:103:104
 foo:0.03:asdf:103:105
 ret=[s1:foobar s2:foobar age:25 pi:3.14]
-"""
-    doAssert output == expected, output
-    doAssert exitCode == 0
+""", output
 
 else: # don't run twice the same test
-  import std/[strutils]
+  import std/strutils
   template check2(msg) = doAssert msg in output, output
 
   block: # tests with various options `nim doc --project --index --docroot`
@@ -142,17 +145,16 @@ sub/mmain.idx""", context
       else: doAssert false
 
   block: # mstatic_assert
-    let (output, exitCode) = runCmd("ccgbugs/mstatic_assert.nim", "-d:caseBad")
+    let (output, exitCode) = runNimCmd("ccgbugs/mstatic_assert.nim", "-d:caseBad")
     check2 "sizeof(bool) == 2"
     check exitCode != 0
 
   block: # ABI checks
     let file = "misc/msizeof5.nim"
     block:
-      let (output, exitCode) = runCmd(file, "-d:checkAbi")
-      doAssert exitCode == 0, output
+      discard runNimCmdChk(file, "-d:checkAbi")
     block:
-      let (output, exitCode) = runCmd(file, "-d:checkAbi -d:caseBad")
+      let (output, exitCode) = runNimCmd(file, "-d:checkAbi -d:caseBad")
       # on platforms that support _StaticAssert natively, errors will show full context, e.g.:
       # error: static_assert failed due to requirement 'sizeof(unsigned char) == 8'
       # "backend & Nim disagree on size for: BadImportcType{int64} [declared in mabi_check.nim(1, 6)]"
@@ -293,3 +295,25 @@ tests/newconfig/bar/mfoo.nims""".splitLines
         let (outp, exitCode) = run "echo 1+2; quit(2)"
         check3 "3" in outp
         doAssert exitCode == 2
+
+  block: # nimBetterRun
+    let file = "misc/mbetterrun.nim"
+    const nimcache2 = buildDir / "D20210423T185116"
+    removeDir nimcache2
+    # related to `-d:nimBetterRun`
+    let opt = fmt"-r --usenimcache --nimcache:{nimcache2}"
+    var ret = ""
+    for a in @["v1", "v2", "v1", "v3"]:
+      ret.add runNimCmdChk(file, fmt"{opt} -d:mbetterrunVal:{a}")
+    ret.add runNimCmdChk(file, fmt"{opt} -d:mbetterrunVal:v2", rtarg = "arg1 arg2")
+      # rt arguments should not cause a recompilation
+    doAssert ret == """
+compiling: v1
+running: v1
+compiling: v2
+running: v2
+running: v1
+compiling: v3
+running: v3
+running: v2
+""", ret