vs: respect 'b_pch' option

Fixes #4681.

mesonbuild/backend/vs2010backend.py

@@ -982,7 +982,6 @@ class Vs2010Backend(backends.Backend):
         target_defines.append('%(PreprocessorDefinitions)')
         ET.SubElement(clconf, 'PreprocessorDefinitions').text = ';'.join(target_defines)
         ET.SubElement(clconf, 'FunctionLevelLinking').text = 'true'
-        pch_node = ET.SubElement(clconf, 'PrecompiledHeader')
         # Warning level
         warning_level = self.get_option_for_target('warning_level', target)
         ET.SubElement(clconf, 'WarningLevel').text = 'Level' + str(1 + int(warning_level))
@@ -990,6 +989,8 @@ class Vs2010Backend(backends.Backend):
             ET.SubElement(clconf, 'TreatWarningAsError').text = 'true'
         # Note: SuppressStartupBanner is /NOLOGO and is 'true' by default
         pch_sources = {}
+        if self.environment.coredata.base_options.get('b_pch', False):
+            pch_node = ET.SubElement(clconf, 'PrecompiledHeader')
             for lang in ['c', 'cpp']:
                 pch = target.get_pch(lang)
                 if not pch:

test cases/failing build/3 pch disabled/c/meson.build

@@ -0,0 +1,2 @@
+exe = executable('prog', 'prog.c',
+c_pch : ['pch/prog_pch.c', 'pch/prog.h'])

test cases/failing build/3 pch disabled/c/pch/prog.h

@@ -0,0 +1 @@
+#include<stdio.h>

test cases/failing build/3 pch disabled/c/pch/prog_pch.c

@@ -0,0 +1,5 @@
+#if !defined(_MSC_VER)
+#error "This file is only for use with MSVC."
+#endif
+
+#include "prog.h"

test cases/failing build/3 pch disabled/c/prog.c

@@ -0,0 +1,10 @@
+// No includes here, they need to come from the PCH
+
+void func() {
+    fprintf(stdout, "This is a function that fails if stdio is not #included.\n");
+}
+
+int main(int argc, char **argv) {
+    return 0;
+}
+

test cases/failing build/3 pch disabled/meson.build

@@ -0,0 +1,5 @@
+# Disable PCH usage to make sure backends respect this setting.
+# Since the .c file requires PCH usage (it does not include necessary
+# headers itself), the build should fail.
+project('pch test', 'c', default_options: ['b_pch=false'])
+subdir('c')