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Compiler options

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This article describes compiler command-line options for the F# compiler. The command dotnet build invokes the F# compiler on F# project files. F# project files are noted with the .fsproj extension.

The compilation environment can also be controlled by setting the project properties. For projects targeting .NET Core, the "Other flags" property, <OtherFlags>...</OtherFlags> in .fsproj, is used for specifying extra command-line options.

Compiler Options Listed Alphabetically

The following table shows compiler options listed alphabetically. Some of the F# compiler options are similar to the C# compiler options. If that is the case, a link to the C# compiler options topic is provided.

Compiler Option Description
--allsigs Generates a new (or regenerates an existing) signature file for each source file in the compilation. For more information about signature files, see Signatures.
-a filename.fs Generates a library from the specified file. This option is a short form of --target:library filename.fs.
--baseaddress:address Specifies the preferred base address at which to load a DLL.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /baseaddress (C# Compiler Options).
--codepage:id Specifies which code page to use during compilation if the required page isn't the current default code page for the system.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /code pages (C# Compiler Options).
--consolecolors Specifies that errors and warnings use color-coded text on the console.
--crossoptimize[+ or -] Enables or disables cross-module optimizations.
--delaysign[+|-] Delay-signs the assembly using only the public portion of the strong name key.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /delaysign (C# Compiler Options).
--checked[+|-] Enables or disables the generation of overflow checks.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /checked (C# Compiler Options).
--debug[+|-]

-g[+|-]

--debug:[full|pdbonly]

-g: [full|pdbonly]		 Enables or disables the generation of debug information, or specifies the type of debug information to generate. The default is full, which allows attaching to a running program. Choose pdbonly to get limited debugging information stored in a pdb (program database) file.

Equivalent to the C# compiler option of the same name. For more information, see

/debug (C# Compiler Options).
--define:symbol

-d:symbol		 Defines a symbol for use in conditional compilation.
--deterministic[+|-] Produces a deterministic assembly (including module version GUID and timestamp). This option cannot be used with wildcard version numbers, and only supports embedded and portable debugging types
--doc:xmldoc-filename Instructs the compiler to generate XML documentation comments to the file specified. For more information, see XML Documentation.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /doc (C# Compiler Options).
--fullpaths Instructs the compiler to generate fully qualified paths.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /fullpaths (C# Compiler Options).
--help

-?		 Displays usage information, including a brief description of all the compiler options.
--highentropyva[+|-] Enable or disable high-entropy address space layout randomization (ASLR), an enhanced security feature. The OS randomizes the locations in memory where infrastructure for applications (such as the stack and heap) are loaded. If you enable this option, operating systems can use this randomization to use the full 64-bit address-space on a 64-bit machine.
--keycontainer:key-container-name Specifies a strong name key container.
--keyfile:filename Specifies the name of a public key file for signing the generated assembly.
--lib:folder-name

-I:folder-name		 Specifies a directory to be searched for assemblies that are referenced.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /lib (C# Compiler Options).
--linkresource:resource-info Links a specified resource to the assembly. The format of resource-info is filename[name[public|private]]

Linking a single resource with this option is an alternative to embedding an entire resource file with the --resource option.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /linkresource (C# Compiler Options).
--mlcompatibility Ignores warnings that appear when you use features that are designed for compatibility with other versions of ML.
--noframework Disables the default reference to the .NET Framework assembly.
--nointerfacedata Instructs the compiler to omit the resource it normally adds to an assembly that includes F#-specific metadata.
--nologo Doesn't show the banner text when launching the compiler.
--nooptimizationdata Instructs the compiler to only include optimization essential for implementing inlined constructs. Inhibits cross-module inlining but improves binary compatibility.
--nowin32manifest Instructs the compiler to omit the default Win32 manifest.
--nowarn:warning-number-list Disables specific warnings listed by number. Separate each warning number by a comma. You can discover the warning number for any warning from the compilation output.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /nowarn (C# Compiler Options).
--optimize[+|-] [optimization-option-list]

-O[+|-] [optimization-option-list]		 Enables or disables optimizations. Some optimization options can be disabled or enabled selectively by listing them. These are: nojitoptimize, nojittracking, nolocaloptimize, nocrossoptimize, notailcalls.
--out:output-filename

-o:output-filename		 Specifies the name of the compiled assembly or module.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /out (C# Compiler Options).
--pathmap:path=sourcePath,... Specifies how to map physical paths to source path names output by the compiler.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /pathmap (C# Compiler Options).
--pdb:pdb-filename Names the output debug PDB (program database) file. This option only applies when --debug is also enabled.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /pdb (C# Compiler Options).
--platform:platform-name Specifies that the generated code will only run on the specified platform (x86, Itanium, or x64), or, if the platform-name anycpu is chosen, specifies that the generated code can run on any platform.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /platform (C# Compiler Options).
--preferreduilang:lang Specifies the preferred output language culture name (for example, es-ES, ja-JP).
--quotations-debug Specifies that extra debugging information should be emitted for expressions that are derived from F# quotation literals and reflected definitions. The debug information is added to the custom attributes of an F# expression tree node. See Code Quotations and Expr.CustomAttributes.
--reference:assembly-filename

-r:assembly-filename		 Makes code from an F# or .NET Framework assembly available to the code being compiled.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /reference (C# Compiler Options).
--resource:resource-filename Embeds a managed resource file into the generated assembly.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /resource (C# Compiler Options).
--sig:signature-filename Generates a signature file based on the generated assembly. For more information about signature files, see Signatures.
--simpleresolution Specifies that assembly references should be resolved using directory-based Mono rules rather than MSBuild resolution. The default is to use MSBuild resolution except when running under Mono.
--standalone Specifies to produce an assembly that contains all of its dependencies so that it runs by itself without the need for additional assemblies, such as the F# library.
--staticlink:assembly-name Statically links the given assembly and all referenced DLLs that depend on this assembly. Use the assembly name, not the DLL name.
--subsystemversion Specifies the version of the OS subsystem to be used by the generated executable. Use 6.02 for Windows 8.1, 6.01 for Windows 7, 6.00 for Windows Vista. This option only applies to executables, not DLLs, and need only be used if your application depends on specific security features available only on certain versions of the OS. If this option is used, and a user attempts to execute your application on a lower version of the OS, it will fail with an error message.
--tailcalls[+|-] Enables or disables the use of the tail IL instruction, which causes the stack frame to be reused for tail recursive functions. This option is enabled by default.
--target:[exe|winexe|library|module] filename Specifies the type and file name of the generated compiled code.
  • exe means a console application.
  • winexe means a Windows application, which differs from the console application in that it does not have standard input/output streams (stdin, stdout, and stderr) defined.
  • library is an assembly without an entry point.
  • module is a .NET Framework module (.netmodule), which can later be combined with other modules into an assembly.
--times Displays timing information for compilation.
--utf8output Enables printing compiler output in the UTF-8 encoding.
--warn:warning-level Sets a warning level (0 to 5). The default level is 3. Each warning is given a level based on its severity. Level 5 gives more, but less severe, warnings than level 1.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /warn (C# Compiler Options).
--warnon:warning-number-list Enable specific warnings that might be off by default or disabled by another command-line option. The list is comma-separated.
--warnaserror[+|-] [warning-number-list] Enables or disables the option to report warnings as errors. You can provide specific warning numbers to be disabled or enabled. Options later in the command line override options earlier in the command line. For example, to specify the warnings that you don't want reported as errors, specify --warnaserror+ --warnaserror-:warning-number-list.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /warnaserror (C# Compiler Options).
--win32manifest:manifest-filename Adds a Win32 manifest file to the compilation. This compiler option is equivalent to the C# compiler option of the same name. For more information, see /win32manifest (C# Compiler Options).
--win32res:resource-filename Adds a Win32 resource file to the compilation.

This compiler option is equivalent to the C# compiler option of the same name. For more information, see /win32res ((C#) Compiler Options).

Opt-in warnings

The F# compiler supports several opt-in warnings:

Number Summary Level Description
21 Recursion checked at run time 5 Warn when a recursive use is checked for initialization-soundness at run time.
22 Bindings executed out of order 5 Warn when a recursive binding may be executed out-of-order because of a forward reference.
52 Implicit copies of structs 5 Warn when an immutable struct is copied to ensure the original is not mutated by an operation.
1178 Implicit equality/comparison 5 Warn when an F# type declaration is implicitly inferred to be NoEquality or NoComparison but the attribute is not present on the type.
1182 Unused variables n/a Warn for unused variables.
3180 Implicit heap allocations n/a Warn when a mutable local is implicitly allocated as a reference cell because it has been captured by a closure.
3366 Index notation n/a Warn when the F# 5 index notation expr.[idx] is used.
3517 InlineIfLambda failure n/a Warn when the F# optimizer fails to inline an InlineIfLambda value, for example if a computed function value has been provided instead of an explicit lambda.
3387 op_Implicit conversion n/a Warn when a .NET implicit conversion is used at a method argument.
3388 Additional implicit upcast n/a Warn when an additional upcast is implicitly used, added in F# 6.
3389 Implicit widening n/a Warn when an implicit numeric widening is used.
3390 Malformed XML doc comments n/a Warn when XML doc comments are malformed in various ways.

You can enable these warnings by using /warnon:NNNN or <WarnOn>NNNN</WarnOn> where NNNN is the relevant warning number. (You may also use the syntax <WarnOn>FSNNNN</WarnOn>, e.g. <WarnOn>FS3388</WarnOn>.) Note that if the WarnOn property is specified multiple times, only the last occurrence is used. To specify multiple warnings, provide the WarnOn property once with a comma-separated string as its contents: <WarnOn>3388,3559</WarnOn>.

Title Description
F# Interactive Options Describes command-line options supported by the F# interpreter, fsi.exe.
Project Properties Reference Describes the UI for projects, including project property pages that provide build options.