Do not warn unused variables inside extern declarations

[dungpa]

Fix #485.

This PR uses the repro by @forki (hope he doesn't mind :) )

See previous discussion at #1861.

[forki]

That's why I did it ;-) awesome

[forki]

That looks good

[KevinRansom]

One test failed, not sure how it is related though:

+++ CodeGen\EmittedIL\TestFunctions (TestFunction10.fs - NetFx40) +++
POSTCMD: [..\CompareIL.cmd TestFunction10.exe NetFx40]

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>REM == TestFunction10.exe --> assembly 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>REM == NetFx40 --> NetFx20|NetFx40 (default is NetFx20) - case insensitive 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>REM ==  --> directory 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if not '' == '' (set dll=\TestFunction10.exe ) 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if '' == '' (set dll=TestFunction10.exe ) 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>REM

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>rem compute the location of ildasm 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>rem

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if exist "" set WINSDKNETFXTOOLS_X86= 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if not "" == "" goto :havesdk 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>set REGEXE32BIT=reg.exe 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\WOW6432Node\Microsoft\Microsoft SDKs\NETFXSDK\4.6.2\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 
ERROR: The system was unable to find the specified registry key or value.

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\" == "" FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\WOW6432Node\Microsoft\Microsoft SDKs\NETFXSDK\4.6.1\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\" == "" FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\Microsoft\Microsoft SDKs\NETFXSDK\4.6\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\" == "" FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\Microsoft\Microsoft SDKs\Windows\v8.1A\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\" == "" FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\Microsoft\Microsoft SDKs\Windows\v8.0A\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\" == "" FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\Microsoft\Microsoft SDKs\Windows\v7.1\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>if "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\" == "" FOR /F "tokens=2* delims=	 " %A IN ('reg.exe QUERY "HKLM\Software\Microsoft\Microsoft SDKs\Windows\v7.0A\WinSDK-NetFx40Tools" /v InstallationFolder') DO SET WINSDKNETFXTOOLS_x86=%B 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>"C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\ildasm.exe" /TEXT /LINENUM /NOBAR TestFunction10.exe  1>TestFunction10.il 
error : File 'TestFunction10.exe' not found or not a PE file

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>IF NOT ERRORLEVEL 0 exit 1 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>IF /I "NetFx40" == "NetFx40" goto :NetFx4 

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>..\..\..\..\testenv\bin\ILComparer.exe "TestFunction10.il.netfx4.bsl" "TestFunction10.il" 
Files differ at line 1:
	>> .assembly extern mscorlib
	>> {
	>>   .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
	>>   .ver 4:0:0:0
	>> }
	>> .assembly extern FSharp.Core
	>> {
	>>   .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
	>>   .ver 4:0:0:0
	>> }
	>> .assembly TestFunction10
	>> {
	>>   .custom instance void [FSharp.Core]Microsoft.FSharp.Core.FSharpInterfaceDataVersionAttribute::.ctor(int32,
	>>                                                                                                       int32,
	>>                                                                                                       int32) = ( 01 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 ) 
	>>   .hash algorithm 0x00008004
	>>   .ver 0:0:0:0
	>> }
	>> .mresource public FSharpSignatureData.TestFunction10
	>> {
	>> }
	>> .mresource public FSharpOptimizationData.TestFunction10
	>> {
	>> }
	>> .module TestFunction10.exe
	>> .imagebase 0x00400000
	>> .file alignment 0x00000200
	>> .stackreserve 0x00100000
	>> .subsystem 0x0003       // WINDOWS_CUI
	>> .corflags 0x00000001    //  ILONLY
	>> .class public abstract auto ansi sealed TestFunction10
	>>        extends [mscorlib]System.Object
	>> {
	>>   .custom instance void [FSharp.Core]Microsoft.FSharp.Core.CompilationMappingAttribute::.ctor(valuetype [FSharp.Core]Microsoft.FSharp.Core.SourceConstructFlags) = ( 01 00 07 00 00 00 00 00 ) 
	>>   .method public static int32  TestFunction10(int32 p_0,
	>>                                               int32 p_1) cil managed
	>>   {
	>>     .maxstack  4
	>>     .locals init ([0] class [mscorlib]System.Tuple`2<int32,int32> p,
	>>              [1] class [mscorlib]System.Tuple`2<int32,int32> V_1,
	>>              [2] int32 y,
	>>              [3] int32 x)
	>>     .language '{AB4F38C9-B6E6-43BA-BE3B-58080B2CCCE3}', '{994B45C4-E6E9-11D2-903F-00C04FA302A1}', '{5A869D0B-6611-11D3-BD2A-0000F80849BD}'
	>>     .line 5,5 : 5,18 
	>>     IL_0000:  ldarg.0
	>>     IL_0001:  ldarg.1
	>>     IL_0002:  newobj     instance void class [mscorlib]System.Tuple`2<int32,int32>::.ctor(!0,
	>>                                                                                           !1)
	>>     IL_0007:  stloc.0
	>>     IL_0008:  nop
	>>     IL_0009:  ldloc.0
	>>     IL_000a:  stloc.1
	>>     IL_000b:  ldloc.1
	>>     IL_000c:  call       instance !1 class [mscorlib]System.Tuple`2<int32,int32>::get_Item2()
	>>     IL_0011:  stloc.2
	>>     IL_0012:  ldloc.1
	>>     IL_0013:  call       instance !0 class [mscorlib]System.Tuple`2<int32,int32>::get_Item1()
	>>     IL_0018:  stloc.3
	>>     .line 6,6 : 5,8 
	>>     IL_0019:  ldloc.3
	>>     IL_001a:  ldloc.2
	>>     IL_001b:  add
	>>     IL_001c:  ret
	>>   } // end of method TestFunction10::TestFunction10
	>> } // end of class TestFunction10
	>> .class private abstract auto ansi sealed '<StartupCode$TestFunction10>'.$TestFunction10
	>>        extends [mscorlib]System.Object
	>> {
	>>   .method public static void  main@() cil managed
	>>   {
	>>     .entrypoint
	>>     .maxstack  8
	>>     IL_0000:  nop
	>>     IL_0001:  ret
	>>   } // end of method $TestFunction10::main@
	>> } // end of class '<StartupCode$TestFunction10>'.$TestFunction10
	<< EOF

D:\j\workspace\release_ci_pa---3f142ccc\tests\fsharpqa\Source\CodeGen\EmittedIL\TestFunctions>exit /b 1 
Fail to execute the POSTCMD. FAIL

[dungpa]

I also think it's not related.

@dotnet-bot test this please

[KevinRansom]

@dungpa

Thank you for adding this.

Kevin