Vs backend compiler selection (#5448)

* backends/vs: Only set platform_toolset if it isn't already set

* interpreter: set backend up after the compiler

Otherwise we won't be able to check which VS toolchain to use.

* docs/using-visual-studio: wrap lines

* docs: recommend the py launcher instead of python3 for windows

* set backend.environment when building a dummy version

* backends/vs: Add support for clang-cl with vs2017 and vs2019 backends

* backends/vs: Add support for ICL (19.x) with vs2015 and vs2017 backends

5 files changed, 43 insertions, 5 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index 40f9411..512eeed 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -157,6 +157,7 @@ class Backend:
         # Make it possible to construct a dummy backend
         # This is used for introspection without a build directory
         if build is None:
+            self.environment = None
             return
         self.build = build
         self.environment = build.environment
diff --git a/mesonbuild/backend/vs2015backend.py b/mesonbuild/backend/vs2015backend.py
index 29b33fb..1e5e171 100644
--- a/mesonbuild/backend/vs2015backend.py
+++ b/mesonbuild/backend/vs2015backend.py
@@ -13,11 +13,23 @@
 # limitations under the License.
 
 from .vs2010backend import Vs2010Backend
+from ..mesonlib import MesonException
 
 
 class Vs2015Backend(Vs2010Backend):
     def __init__(self, build):
         super().__init__(build)
         self.name = 'vs2015'
-        self.platform_toolset = 'v140'
         self.vs_version = '2015'
+        if self.environment is not None:
+            # TODO: we assume host == build
+            comps = self.environment.coredata.compilers.host
+            if comps and all(c.id == 'intel-cl' for c in comps.values()):
+                c = list(comps.values())[0]
+                if c.version.startswith('19'):
+                    self.platform_toolset = 'Intel C++ Compiler 19.0'
+                else:
+                    # We don't have support for versions older than 2019 right now.
+                    raise MesonException('There is currently no support for ICL before 19, patches welcome.')
+            if self.platform_toolset is None:
+                self.platform_toolset = 'v140'
diff --git a/mesonbuild/backend/vs2017backend.py b/mesonbuild/backend/vs2017backend.py
index 9098226..9308233 100644
--- a/mesonbuild/backend/vs2017backend.py
+++ b/mesonbuild/backend/vs2017backend.py
@@ -16,14 +16,29 @@ import os
 import xml.etree.ElementTree as ET
 
 from .vs2010backend import Vs2010Backend
+from ..mesonlib import MesonException
 
 
 class Vs2017Backend(Vs2010Backend):
     def __init__(self, build):
         super().__init__(build)
         self.name = 'vs2017'
-        self.platform_toolset = 'v141'
         self.vs_version = '2017'
+        # We assume that host == build
+        if self.environment is not None:
+            comps = self.environment.coredata.compilers.host
+            if comps:
+                if comps and all(c.id == 'clang-cl' for c in comps.values()):
+                    self.platform_toolset = 'llvm'
+                elif comps and all(c.id == 'intel-cl' for c in comps.values()):
+                    c = list(comps.values())[0]
+                    if c.version.startswith('19'):
+                        self.platform_toolset = 'Intel C++ Compiler 19.0'
+                    else:
+                        # We don't have support for versions older than 2019 right now.
+                        raise MesonException('There is currently no support for ICL before 19, patches welcome.')
+        if self.platform_toolset is None:
+            self.platform_toolset = 'v141'
         # WindowsSDKVersion should be set by command prompt.
         sdk_version = os.environ.get('WindowsSDKVersion', None)
         if sdk_version:
diff --git a/mesonbuild/backend/vs2019backend.py b/mesonbuild/backend/vs2019backend.py
index c6e78cb..c0ff5c3 100644
--- a/mesonbuild/backend/vs2019backend.py
+++ b/mesonbuild/backend/vs2019backend.py
@@ -22,8 +22,18 @@ class Vs2019Backend(Vs2010Backend):
     def __init__(self, build):
         super().__init__(build)
         self.name = 'vs2019'
-        self.platform_toolset = 'v142'
-        self.vs_version = '2019'
+        if self.environment is not None:
+            comps = self.environment.coredata.compilers.host
+            if comps and all(c.id == 'clang-cl' for c in comps.values()):
+                self.platform_toolset = 'llvm'
+            elif comps and all(c.id == 'intel-cl' for c in comps.values()):
+                c = list(comps.values())[0]
+                if c.version.startswith('19'):
+                    self.platform_toolset = 'Intel C++ Compiler 19.0'
+                # We don't have support for versions older than 2019 right now.
+            if not self.platform_toolset:
+                self.platform_toolset = 'v142'
+            self.vs_version = '2019'
         # WindowsSDKVersion should be set by command prompt.
         sdk_version = os.environ.get('WindowsSDKVersion', None)
         if sdk_version:
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index cc0dae0..5f69e22 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2710,7 +2710,6 @@ external dependencies (including libraries) must go to "dependencies".''')
         else:
             default_options = {}
         self.coredata.set_default_options(default_options, self.subproject, self.environment)
-        self.set_backend()
 
         if not self.is_subproject():
             self.build.project_name = proj_name
@@ -2745,6 +2744,7 @@ external dependencies (including libraries) must go to "dependencies".''')
         mlog.log('Project name:', mlog.bold(proj_name))
         mlog.log('Project version:', mlog.bold(self.project_version))
         self.add_languages(proj_langs, True)
+        self.set_backend()
         if not self.is_subproject():
             self.check_stdlibs()