cgen: produce cleaner error on missing C headers (with optional explanation) (#6637)

Implements support for `#include <openssl/rand.h> # Please install OpenSSL`.

vlib/net/openssl/c.v

@@ -15,7 +15,7 @@ module openssl
 // Brew
 #flag darwin -I/usr/local/opt/openssl/include
 #flag darwin -L/usr/local/opt/openssl/lib
-#include <openssl/rand.h>
+#include <openssl/rand.h> # Please install OpenSSL
 #include <openssl/ssl.h>
 #include <openssl/err.h>
 

vlib/v/ast/ast.v

@@ -628,8 +628,10 @@ pub:
 	mod  string
 	pos  token.Position
 pub mut:
-	val  string
-	kind string
+	val  string // example: 'include <openssl/rand.h> # please install openssl // comment'
+	kind string // : 'include'
+	main string // : '<openssl/rand.h>'
+	msg  string // : 'please install openssl'
 }
 
 /*

vlib/v/builder/cc.v

@@ -10,7 +10,8 @@ import v.pref
 import term
 
 const (
-	c_error_info      = '
+	c_verror_message_marker = 'VERROR_MESSAGE '
+	c_error_info            = '
 ==================
 C error. This should never happen.
 
@@ -20,7 +21,7 @@ https://github.com/vlang/v/issues/new/choose
 
 You can also use #help on Discord: https://discord.gg/vlang
 '
-	no_compiler_error = '
+	no_compiler_error       = '
 ==================
 Error: no C compiler detected.
 
@@ -75,6 +76,37 @@ fn (mut v Builder) find_win_cc() ? {
 	v.pref.ccompiler_type = pref.cc_from_string(v.pref.ccompiler)
 }
 
+fn (mut v Builder) post_process_c_compiler_output(res os.Result) {
+	if res.exit_code == 0 {
+		return
+	}
+	for emsg_marker in [c_verror_message_marker, 'error: include file '] {
+		if res.output.contains(emsg_marker) {
+			emessage := res.output.all_after(emsg_marker).all_before('\n').all_before('\r').trim_right('\r\n')
+			verror(emessage)
+		}
+	}
+	if v.pref.is_debug {
+		eword := 'error:'
+		khighlight := if term.can_show_color_on_stdout() { term.red(eword) } else { eword }
+		println(res.output.trim_right('\r\n').replace(eword, khighlight))
+	} else {
+		if res.output.len < 30 {
+			println(res.output)
+		} else {
+			elines := error_context_lines(res.output, 'error:', 1, 12)
+			println('==================')
+			for eline in elines {
+				println(eline)
+			}
+			println('...')
+			println('==================')
+			println('(Use `v -cg` to print the entire error message)\n')
+		}
+	}
+	verror(c_error_info)
+}
+
 fn (mut v Builder) cc() {
 	if os.executable().contains('vfmt') {
 		return
@@ -491,49 +523,28 @@ fn (mut v Builder) cc() {
 		verror(err)
 		return
 	}
-	if res.exit_code != 0 {
-		// the command could not be found by the system
-		if res.exit_code == 127 {
-			$if linux {
-				// TCC problems on linux? Try GCC.
-				if ccompiler.contains('tcc') {
-					v.pref.ccompiler = 'cc'
-					goto start
-				}
-			}
-			verror('C compiler error, while attempting to run: \n' +
-				'-----------------------------------------------------------\n' + '$cmd\n' +
-				'-----------------------------------------------------------\n' + 'Probably your C compiler is missing. \n' +
-				'Please reinstall it, or make it available in your PATH.\n\n' + missing_compiler_info())
-		}
-		if v.pref.is_debug {
-			eword := 'error:'
-			khighlight := if term.can_show_color_on_stdout() { term.red(eword) } else { eword }
-			println(res.output.trim_right('\r\n').replace(eword, khighlight))
-			verror(c_error_info)
-		} else {
-			if res.output.len < 30 {
-				println(res.output)
-			} else {
-				elines := error_context_lines(res.output, 'error:', 1, 12)
-				println('==================')
-				for eline in elines {
-					println(eline)
-				}
-				println('...')
-				println('==================')
-				println('(Use `v -cg` to print the entire error message)\n')
-			}
-			verror(c_error_info)
-		}
-	}
 	diff := time.ticks() - ticks
+	v.timing_message('C ${ccompiler:3}', diff)
+	if res.exit_code == 127 {
+		// the command could not be found by the system
+		$if linux {
+			// TCC problems on linux? Try GCC.
+			if ccompiler.contains('tcc') {
+				v.pref.ccompiler = 'cc'
+				goto start
+			}
+		}
+		verror('C compiler error, while attempting to run: \n' +
+			'-----------------------------------------------------------\n' + '$cmd\n' +
+			'-----------------------------------------------------------\n' + 'Probably your C compiler is missing. \n' +
+			'Please reinstall it, or make it available in your PATH.\n\n' + missing_compiler_info())
+	}
+	v.post_process_c_compiler_output(res)
 	// Print the C command
 	if v.pref.is_verbose {
 		println('$ccompiler took $diff ms')
 		println('=========\n')
 	}
-	v.timing_message('C ${ccompiler:3}', diff)
 	// Link it if we are cross compiling and need an executable
 	/*
 	if v.os == .linux && !linux_host && v.pref.build_mode != .build {

vlib/v/builder/msvc.v

@@ -308,9 +308,7 @@ pub fn (mut v Builder) cc_msvc() {
 	}
 	diff := time.ticks() - ticks
 	v.timing_message('C msvc', diff)
-	if res.exit_code != 0 {
-		verror(res.output)
-	}
+	v.post_process_c_compiler_output(res)
 	// println(res)
 	// println('C OUTPUT:')
 	// Always remove the object file - it is completely unnecessary

vlib/v/checker/checker.v

@@ -2459,7 +2459,7 @@ fn (mut c Checker) hash_stmt(mut node ast.HashStmt) {
 		return
 	}
 	if node.kind == 'include' {
-		mut flag := node.val[8..]
+		mut flag := node.main
 		if flag.contains('@VROOT') {
 			vroot := util.resolve_vroot(flag, c.file.path) or {
 				c.error(err, node.pos)
@@ -2475,7 +2475,7 @@ fn (mut c Checker) hash_stmt(mut node ast.HashStmt) {
 		}
 	} else if node.kind == 'flag' {
 		// #flag linux -lm
-		mut flag := node.val[5..]
+		mut flag := node.main
 		// expand `@VROOT` to its absolute path
 		if flag.contains('@VROOT') {
 			flag = util.resolve_vroot(flag, c.file.path) or {

vlib/v/checker/tests/missing_c_lib_header_1.out

@@ -0,0 +1 @@
+builder error: Header file <missing/folder/header1.h>, needed for module `main` was not found. Please install the corresponding development headers.

vlib/v/checker/tests/missing_c_lib_header_1.vv

@@ -0,0 +1,6 @@
+module main
+
+// The following header file is intentionally missing.
+// The #include does not have the optional explanation part
+// after a `#` sign:
+#include <missing/folder/header1.h>

vlib/v/checker/tests/missing_c_lib_header_with_explanation_2.out

@@ -0,0 +1 @@
+builder error: Header file <missing/folder/header.h>, needed for module `main` was not found. Please install missing C library.

vlib/v/checker/tests/missing_c_lib_header_with_explanation_2.vv

@@ -0,0 +1,6 @@
+module main
+
+// The following header file is intentionally missing.
+// The part after `#` is an explanation message, that V will
+// show, when it is not found:
+#include <missing/folder/header.h> # Please install missing C library

vlib/v/compiler_errors_test.v

@@ -85,6 +85,13 @@ fn (mut tasks []TaskDescription) run() {
 	$if noskip ? {
 		m_skip_files = []
 	}
+	$if tinyc {
+		// NB: tcc does not support __has_include, so the detection mechanism
+		// used for the other compilers does not work. It still provides a
+		// cleaner error message, than a generic C error, but without the explanation.
+		m_skip_files << 'vlib/v/checker/tests/missing_c_lib_header_1.vv'
+		m_skip_files << 'vlib/v/checker/tests/missing_c_lib_header_with_explanation_2.vv'
+	}
 	for i in 0 .. tasks.len {
 		if tasks[i].path in m_skip_files {
 			tasks[i].is_skipped = true

vlib/v/gen/cgen.v

@@ -960,18 +960,41 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 		ast.HashStmt {
 			// #include etc
 			if node.kind == 'include' {
-				if node.val.contains('.m') {
+				mut missing_message := 'Header file $node.main, needed for module `$node.mod` was not found.'
+				if node.msg != '' {
+					missing_message += ' ${node.msg}.'
+				} else {
+					missing_message += ' Please install the corresponding development headers.'
+				}
+				mut guarded_include := '
+				|#if defined(__has_include)
+				|
+				|#if __has_include($node.main)
+				|#include $node.main
+				|#else
+				|#error VERROR_MESSAGE $missing_message
+				|#endif
+				|
+				|#else
+				|#include $node.main
+				|#endif
+				'.strip_margin()
+				if node.main == '<errno.h>' {
+					// fails with musl-gcc and msvc; but an unguarded include works:
+					guarded_include = '#include $node.main'
+				}
+				if node.main.contains('.m') {
 					// Objective C code import, include it after V types, so that e.g. `string` is
 					// available there
 					g.definitions.writeln('// added by module `$node.mod`:')
-					g.definitions.writeln('#$node.val')
+					g.definitions.writeln(guarded_include)
 				} else {
 					g.includes.writeln('// added by module `$node.mod`:')
-					g.includes.writeln('#$node.val')
+					g.includes.writeln(guarded_include)
 				}
 			} else if node.kind == 'define' {
 				g.includes.writeln('// defined by module `$node.mod`:')
-				g.includes.writeln('#$node.val')
+				g.includes.writeln('#define $node.main')
 			}
 		}
 		ast.Import {}

vlib/v/parser/comptime.v

@@ -22,11 +22,23 @@ fn (mut p Parser) hash() ast.HashStmt {
 	val := p.tok.lit
 	kind := val.all_before(' ')
 	p.next()
+	mut main := ''
+	mut msg := ''
+	content := val.all_after('$kind ').all_before('//')
+	if content.contains(' #') {
+		main = content.all_before(' #').trim_space()
+		msg = content.all_after(' #').trim_space()
+	} else {
+		main = content.trim_space()
+		msg = ''
+	}
 	// p.trace('a.v', 'kind: ${kind:-10s} | pos: ${pos:-45s} | hash: $val')
 	return ast.HashStmt{
 		mod: p.mod
 		val: val
 		kind: kind
+		main: main
+		msg: msg
 		pos: pos
 	}
 }

vlib/vweb/tests/vweb_test_server.v

@@ -70,7 +70,7 @@ pub fn (mut app App) settings(username string) vweb.Result {
 }
 
 ['/:user/:repo/settings']
-pub fn (mut app App) user_repo_settings(username, repository string) vweb.Result {
+pub fn (mut app App) user_repo_settings(username string, repository string) vweb.Result {
 	if username !in known_users {
 		return app.vweb.not_found()
 	}